Optometry and Vision Science

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In silico and In vitro Discovery of Plant-Based Pro-Inflammatory Cytokine Inhibitors
(University of Waterloo, 2025-10-28) Huynh, Cassandra
Purpose: Dry eye disease (DED) is a prevalent condition range between 44.2% to 62.9% of the population, with female sex and aging being the greatest risk factors. The pathogenesis of DED is based on the dysregulation of tear film homeostasis, resulting in a vicious circle of desiccating stress, inflammation, and tissue damage. Mild DED is managed with artificial tears and warm compresses, whereas moderate-to-severe DED require additional anti-inflammatory therapies to break the vicious circle. Anti-inflammatory drugs such as corticosteroids are effective treatments but are associated with adverse side effects including increased risk of cataracts and glaucoma. Discovering novel anti-inflammatory therapeutics with minimal adverse side effects would greatly benefit DED patients who depend on anti-inflammatory treatment to mitigate symptoms. Flavonoids are a class of chemicals found in all vegetation; some are known for their anti-inflammatory effects. The numerous members of the flavonoid class could be leveraged to discover novel inhibitors against inflammatory DED targets. The purpose of this thesis was to discover a novel flavonoid that could act as an anti-inflammatory agent to treat DED. Methods: This thesis employed a hybrid approach using network analysis, computational modelling, and in vitro validation. Network analysis was employed to select DED-associated protein targets and candidate flavonoids. “Dry Eye Syndrome” proteins were extracted from the STRING-DISEASE database and were cross-referenced with drug databanks using the functional enrichment analysis tool, ToppFun, for flavonoids. A network analysis tool, Cytoscape (v 3.9.1.), was utilized to visualize and rank DED-associated proteins and flavonoids by number of edge interactions. Two proteins were selected for their distinct roles in the immune response, and two flavonoids were selected for their association with multiple pro-inflammatory DED-associated proteins. Molecular docking and molecular dynamic (MD) simulations modelled and simulated the protein-ligand complex of both protein targets with each flavonoid molecule. Four protein-ligand complexes were assessed for stability and specific residue-ligand interactions. The inhibitory effects of both flavonoids were assessed in vitro with ELISAs against both protein targets. The biocompatibility of the most effective flavonoid inhibitor was assessed with human corneal epithelial cells (HCEC) using an Alamar Blue metabolic activity assay; viability was assessed by evaluating the proportion of live, apoptotic, and dead cells. Results: The network analysis generated a protein-protein interaction network of 64 DED-associated proteins and a drug-protein network of 108 flavonoids. Tumour necrosis factor (TNF) 𝛂 interactions and interleukin (IL) 17A (14 interactions) were amongst the 5 highly ranked proteins and selected for their roles in the innate and adaptive immune response, respectively. Luteolin (19 interactions) and rutin (17 interactions) were the highest ranked flavonoids associated with DED-associated proteins. Molecular docking and MD simulations predicted that both flavonoids could bind directly to the receptor binding sites of both cytokines. However, ELISAs showed that neither luteolin nor rutin could inhibit TNF-𝛂 and TNF receptor interaction (all p≥0.07). On the other hand, both luteolin (IC50 = 16.54 mM) and rutin (IC50 = 8.73 mM) had inhibitory effects against IL-17A and IL-17A receptor interaction (all p<0.01). Metabolic activity and viability of HCEC remained high (all ≥ 85.95%) below 3.0 mM rutin; no significant difference in metabolic activity and viability were detected in all concentrations of rutin compared to the control (all p>0.06). Conclusion: This thesis identified rutin as a novel flavonoid inhibitor of IL-17A. These findings suggest that rutin may play a role in anti-inflammatory therapeutics for DED.
Electroretinograms following short-term chromatic light adaptation in high myopes and non-myopes
(University of Waterloo, 2025-10-17) Bidarkar, Ashita
Purpose: Worldwide, myopia cases are on the rise and the need for finding a definitive mechanism by which myopia develops has become more imperative than ever before. Axial elongation in myopic eyes is linked to short wavelength (λ) light-dependent increases in retinal dopamine (DA). DA is associated with enhanced electroretinogram (ERG) amplitudes. This thesis seeks to examine short-term adaptation to short and long λ light at moderate and strong levels. I hypothesize that short λ light exposure differentially affects full-field ERGs (ffERGs) and central ERGs in myopic eyes compared to controls. Methods: In a multi-visit cross-over design, we compared ERGs before and after 20 minutes of full-field adaptation to long (red LED peak λ (λ 627 nm) or short (blue LED peak λ 448 nm) λ light (Espion ColorDome™, Diagnosys LLC). Human participants (ages 18-30) were healthy high myopes (≤-5 diopters (D)) and emmetropes (+1 D to - 0.25 D). Monocular, light-adapted (LA) ffERGs were recorded using skin electrodes and a handheld system that adjusted for pupil diameter in real time (RETeval™). ERG stimuli were LA standard white flash and flicker (85 Td.s), presented at 2 and 28.3 Hz, respectively. The a-wave, b-wave and flicker ERG amplitudes, and implicit times were compared as a function of pre/post adaption (time), adapting stimulus (λ), and refractive error (RE) group using a mixed model ANOVA. Monocular multi-focal ERGs (mfERGs; 61 hexagons) and pattern ERGs (PERGs; 15° field, 15’ reversing checks) were recorded with natural pupils in keeping with ISCEV standards using DTL electrodes. The Espion™ console and amplifier (Diagnosys LLC) was used for both ERG tests. The primary outcome measures analyzed were the amplitudes and implicit times of the mfERG central wavelet, mfERG average of the surrounding rings and the PERG P50 peak and were compared as a function of pre/post adaption (time), adapting stimulus (λ), and RE group using a mixed model ANOVA. Results: There were no significant differences between controls and myopes prior to adaptation (all p≥0.05) for ffERG tests. The luminance of the light had an effect such that changes in b-wave implicit time decreased with adaptation to 300 cd/m² light in controls (blue 30: -0.451 ± 1.28%; blue 300: -2.28 ± 2.56%; p≤0.001, η2G=0.14) but less so in the high myope group (blue 30: +0.05 ± 1.3%; blue 300: -1.26 ± 2.43%; p=0.01, η2G=0.05). Changes in flicker implicit time decreased with the stronger luminance level but were not different between refractive error groups (i.e. controls: blue 30: 0.15 ± 1.0%; blue 300: -1.05 ± 1.61%, myopes: blue 30: +0.44 ± 2.74%; blue 300: -1.1 ± 1.50%, p≤0.001, η2G=0.13). Stronger light conditions caused b-wave amplitudes to become less negative (smaller) (i.e. controls: blue 30: –5.38 ± 15.6%; blue 300: –3.50 ± 17.7%, myopes: blue 30: –10.9 ± 15.4%; blue 300: +0.85 ± 10.9%, p=0.02, η2G=0.05). Similarly, with v flicker amplitudes, they became less negative (smaller) with stronger luminance adaptation (i.e. controls: blue 30: –4.1 ± 13.4%; blue 300: –0.62 ± 17.1%, myopes: blue 30: –9.9 ± 18.3%; blue 300: +4.7 ± 12.0%, p=0.00, η2G=0.07). When comparing between controls and high myopes or between short and long wavelengths, changes in b-wave amplitudes did not differ. There was a significant difference between RE groups for the PERG P50 amplitude prior to adaptation (p=0.03; Cohen’s d=1.06) such that they were significantly smaller in myopes (2.63 ± 1.0 μV) than controls (3.95 ± 1.5 μV). The N95 amplitudes were also smaller (i.e. less negative) in myopes (-4.39 ± 1.82 μV) than controls (-6.58 ± 1.55 μV; p= 0.01; Cohen’s d=-1.3). The mfERGs showed no significant pre-adaptation RE differences (all p≥ 0.05; all η2G≤ 0.07). For the PERG, in both controls and myopes, the change in N95 amplitudes decreased more with long λ light (controls: -16.6 ± 23.4%; myopes: -24.7 ± 43.4%) than short λ light (controls: +10.4 ± 23.5%; myopes: +1.88 ± 26.7%; p≤ 0.001; η2G=0.541). There were no effects of adaptation on the P50 amplitude or implicit time. For mfERG, the change in N1P1 magnitude was not different between controls and myopes and was not different when comparing λs for any of the five rings (p≥ 0.05). Conclusions: There is no evidence that chromatic adaptation has a differential effect on post-adaptation ffERGs in high myopes. Long λ adaptation, especially with stronger luminance, prolongs ERG implicit times, probably reflecting relatively reduced input from the faster long cone system. There is evidence to suggest smaller central retinal responses with the PERG P50 but not with the central wavelet of the mfERG, indicating altered retinal ganglion cell function but not altered central inner retinal function in young adults with myopia. Further studies should focus on confirming whether altered central retinal function persists in adult myopes and whether longer adaptation times would yield a greater RE difference.
Visual Standards in Aviation: Implications for Safety, Performance, and Training Assessment
(University of Waterloo, 2025-10-16) Lynch, Allison
Objectives: The goal of this thesis was to provide evidence to either support the current aviation visual medical standards or to begin to define new ones. Two aspects of vision (visual acuity and contrast sensitivity) were intentionally degraded to assess their effects on flight performance. Four experiments were conducted that examined this topic. Experiment one assessed the flight performance of novice pilots during two simulated flight scenarios: approach to landing or a short flight circuit and landing during clear and calm weather conditions with vision degraded with scattering lenses. Experiment two built on this by having novice and intermediate pilots completed a simulated flight circuit and landing during three adverse weather conditions (high wind, heavy rain or high wind and heavy rain) with their vision degraded by scattering lenses or by defocusing lenses. Experiment three examined whether vision could be used as a probe to evaluate flight instructors. This study had pilot participants complete a simulated flight circuit and landing scenario with their vision degraded using both scattering lenses and defocusing lenses while two flight instructors subjectively assessed their flight performance. The fourth and final experiment expanded on these studies by assessing both the flight performance and stress responses of pilot participants during a simulated flight circuit and landing while their vision was degraded either by scattering lenses or defocusing lenses. Methods: Twenty participants were recruited for study 1. Pilot participants completed either an approach to landing flight simulation or a short flight circuit and landing simulation in clear, calm weather conditions with their vision degraded with scattering lenses to either 6 or 8 levels of degradation respectively. Twenty-six pilot participants were recruited for study 2 where they completed a short flight circuit and landing simulated flight in three weather conditions (wind, rain, wind and rain) with 5 levels of vision degradation. Vision was degraded by either scattering lenses or defocusing lenses. Study three examined using vision as a probe to assess flight instructor agreement and repeatability. Twenty pilot participants completed a simulated short flight circuit with their vision degraded using both scattering and defocusing lenses to 8 different visual acuity levels. There was a total of five flight instructors recruited for study three in which two instructors were present to assess the performance of a single pilot participant. This was repeated on a second day with the same pilot participant and the same flight instructors. Study four examined the effect of vision degradation (either scatter or defocus) on both the flight performance and on pilot stress levels (which were monitored via eye-tracking and heart rate sensors) in thirty-seven pilot participants. These participants were tasked with completing a short flight circuit and landing and some of the participants had randomized minor (increased oil pressure) or major (engine failure) emergency scenarios introduced. Results: Results from all four studies showed that flight performance (vertical speed, airspeed, altitude, pitch, roll, landing hardness, landing accuracy) was not significantly impacted by mild and moderate visual degradation. Only severe degradation had an impact on performance. These studies also show that pilot participant contrast sensitivity may be a better indicator of performance than visual acuity, as declines in performance with milder vision degradation when using defocusing lenses compared to scattering lenses were seen. Studies two through four highlighted the importance of using both objective and subjective grading when assessing pilot performance as it was identified that there was a difference in when objective flight performance metrics (significant at 6/18 with scattering lenses and 6/60 with defocusing lenses) were affected and when flight instructors perceived a change in performance (significant at 6/18 with scattering lenses and 6/120 with defocusing lenses). The final study showed that while at several of the vision degradation levels flight performance was unaffected, pilot participant heart rate and eye-tracking metrics were affected. With heart rate variability and eye tracking metrics (saccade amplitude and saccade velocity) being affected at a degradation level of 6/18. Conclusions: These findings challenge the strict reliance on the use of just visual acuity in the current aviation medical standards. Across four experiments, results showed that flight performance remained largely unaffected when defocus lenses were used but was affected at a much lower visual acuity degradation when scattering lenses were used, suggesting contrast sensitivity may be a more relevant predictor of pilot performance. The studies suggest that current visual medical standards may be unnecessarily strict, thereby restricting the pool of eligible pilots. This work also highlighted the need for a more standardized and evidence-based approach to pilot evaluation. The final experiment further underscored the role of stress in flight safety, as physiological stress responses were observed even when flight performance remained stable. Taken together, these findings suggest that a more comprehensive approach – incorporating contrast sensitivity, objective performance measures, and stress responses – may lead to a more effective and fair pilot vision standard.
Studies on tear evaporation and ocular surface temperature
(University of Waterloo, 2025-09-11) Monfared, Mana
Introduction Evaporative Dry Eye (EDE), the most prevalent subtype of Dry Eye Disease (DED), is primarily driven by excessive tear loss from the ocular surface due to deficiencies in the tear film’s lipid layer. Accurate and repeatable measurement of Tear Evaporation Rate (TER) and related ocular surface parameters, such as Ocular Surface Temperature (OST), Lipid Layer Thickness (LLT), and Non-Invasive Tear Break-Up Time (NITBUT) is essential for understanding tear film instability and guiding clinical decision-making. However, measurement variability, lack of standardized protocols, and limitations in existing instrumentation have hindered the adoption of TER and OST assessment in routine practice. This thesis addresses these challenges through a series of in vitro and in vivo experiments aimed at quantifying tear film dynamics and optimizing measurement methodologies. Overall Aims The primary aim of this research was to characterize tear evaporation and ocular surface thermal behavior under a range of physiological and controlled conditions. This thesis specifically sought to: 1. Quantify the evaporation rates of distilled water versus an aqueous artificial tear solution (TheraTears®) in vitro. 2. Assess how changes in exposed ocular surface area and LLT affect TER using model eyes. 3. Investigate the effect of lipid-based artificial tears on LLT, TER, and NITBUT in vivo (PHASE I). 4. Optimize OST measurement parameters using ResearchIR software to improve accuracy and reproducibility. 5. Examine regional variation in OST and blink-related cooling profiles in vivo (PHASE II). 6. Integrate in vitro and in vivo findings to build a comprehensive model of tear film dynamics with implications for EDE diagnosis. Methods and Materials The experiments were conducted using custom-built and commercially available devices. In vitro studies used aluminum model eyes with varied surface areas and lipid layer simulations (via CALMO® Eye Spray) to evaluate their effect on TER, measured using the Waterloo Evaporimeter. In vivo studies were performed on healthy participants using the LipiView® II interferometer, OCULUS Keratograph® 5M, and FLIR A655sc thermal camera integrated with ResearchIR software. Data collection included real-time measurements of TER, LLT, NITBUT, and OST, with particular focus on blink-related cooling and temperature gradient analysis. Each experiment followed standardized protocols for blink control, Region of Interest (ROI) selection, and repeatability validation. Statistical analysis was performed using SPSS, with significance set at p < 0.05. Results In vitro results demonstrated no significant difference in TER between distilled water and TheraTears®, suggesting that aqueous-based artificial tears do not provide meaningful evaporative protection. These findings also confirm that both distilled water and TheraTears® may be used interchangeably in laboratory-based evaporation studies where lipid content is not a critical variable. In contrast, increasing LLT using CALMO® spray led to a marked reduction in TER, and model eyes with larger surface areas consistently exhibited higher evaporation rates. In vivo, lipid eye drop instillation produced a significant increase in LLT, a prolongation of NITBUT, and a decrease in TER. OST monitoring revealed distinct blink-related cooling patterns, particularly in eyes with thinner lipid layers. Optimized OST protocols using ResearchIR improved temporal resolution and reproducibility across participants. Phase II confirmed consistent regional temperature variability and strong correlations between LLT, TER, and post-blink cooling. Conclusions This research confirms that LLT and ocular surface area are critical determinants of TER. Non-lipid formulations, such as TheraTears®, are ineffective in limiting TER, while lipid-based interventions significantly improve tear film stability both thermally and structurally. OST can be used as a reliable, non-invasive surrogate for assessing tear film dynamics when measured with optimized protocols. The Waterloo Evaporimeter and ResearchIR-enabled thermography provide robust, reproducible platforms for studying tear evaporation and cooling responses. These findings support a multimodal diagnostic approach integrating TER, LLT, NITBUT, and OST for the evaluation and management of EDE.
Gait kinematics during walking in children with amblyopia
(University of Waterloo, 2025-09-05) Hoare, Lauren
Introduction: Coordination between the eyes and body is important for navigating the environment. Children with amblyopia score lower for walking on standardized tests of motor ability. However, standardized tests do not assess gait kinematics during walking. Here, I investigated the development of gait kinematics during walking under natural binocular viewing conditions in children with amblyopia compared to controls. Methods: A total of 21 children ages 7 to 13 years with amblyogenic factors (14 anisometropia, 7 strabismus) were enrolled in the ‘amblyopia’ group (15∕21 had current amblyopia). An age-similar group of 27 controls were also enrolled. While viewing binocularly, children walked the length of a GAITRite pressure-sensitive walkway and completed 3 conditions of varying complexity: 1) Straight Walk (SW): walk on mat, 2) Isolated Target Walk (IT): walk and step on two-dimensional targets, and 3) Distractor Target Walk (DT): walk and step on two-dimensional targets while avoiding two-dimensional distractors. Gait kinematics were temporal outcomes of normalized velocity (leg lengths/second), cadence (spm), step time (msecs), and stance time, and spatial outcomes of (msecs), step length (cm), step width (cm) and accuracy (%) of stepping on targets or avoiding distractors. Variability in gait kinematics was also examined using the coefficient of variation (COV, %). Results: Temporal and spatial outcomes of gait kinematics did not differ between children with amblyopia and controls. However, the amblyopia group was less accurate at stepping on targets overall than controls (amblyopia, mean±SD=90.8±8.5% vs control, 96.9±3.8%, p=0.003), with less accuracy found in the IT condition (89.7±9.7% vs 96.5±5.3%, p=0.005), and for the far T2 target (87.4±13.9% vs 97.2±5.4%, p=0.001). Lastly, the amblyopia group showed increased variability (i.e., higher COV) for temporal measures, including normalized velocity (8.9±3.0% vs 6.4±3.0%, p=0.007), stance time (5.7±1.8% vs 4.7±1.8%, p=0.049), cadence (5.0±2.4% vs 3.3±1.7%, p=0.005) and step time (4.9±2.5% vs 3.5±2.1%, p=0.040), and for spatial measures, including step length (8.0±2.4% vs 6.4±2.4%, p=0.024) and step width (7.7±2.2% vs 6.11±2.2%, p=0.014). In the amblyopia group, spatial outcomes were correlated with amblyopic eye visual acuity and temporal measures were correlated with stereoacuity. Conclusions: This thesis shows that unbalanced visual input early in life from pediatric eye conditions that cause amblyopia results in variable and inaccurate walking patterns compared to children with age-typical visual development. This pattern of findings is similar to younger children, indicating that the typical development of gait is delayed in children with amblyopia, especially when they have poor binocularity outcomes. These findings point to the importance of typical binocular vision for the development of walking.
Short-Term Effect of Diffusion Optics TechnologyTM (DOT) Contrast Management Spectacle Lenses on Ocular Biometrics and Lag of Accommodation in Emmetropic Children
(University of Waterloo, 2025-05-20) Jabeen, Asiya
Purpose: Myopia, a prevalent refractive error of the eye, is experiencing a rapid increase in prevalence. According to Holden et al., approximately 50% of the global population is projected to be myopic by the year 2050. In response to this growing concern, various myopia control treatments have been developed, including spectacles, contact lenses, and pharmaceutical options. One innovative treatment is the use of Diffusion Optics Technology ™ (DOT) spectacle lenses. These lenses are designed to modulate retinal contrast, thereby reducing signals for axial elongation. The lenses incorporate thousands of microscopic dots to manage contrast, which helps reduce signal disparities between adjacent cones while maintaining good visual acuity and functional peripheral vision. However, there is a lack of published literature on the generalized effects of these contrast management spectacles (CMS) on ocular structures over a short period of wear. This thesis aimed to address this gap and determine the short-term effect of CMS on ocular structures and lag of accommodation. Additionally, the thesis also examined the repeatability of various methods of measurement of choroidal thickness. Methods and Materials: Chapters 3, 4, 5, 6: This study was a two-visit, prospective, randomized, controlled, participant-masked trial involving 30 emmetropic participants aged 8 to 14. The participants’ eligibility was confirmed during a screening visit, which utilized non-cycloplegic auto-refraction to ensure that the spherical equivalent was between +1.00D and -0.75D, with astigmatism not exceeding -0.75DC. During the first study visit, ocular biometrics were assessed using the IOL Master and a Topcon DRI OCT for baseline measurements. The parameters measured included central corneal thickness (CCT), anterior chamber depth (ACD), crystalline lens thickness (LT), retinal thickness, choroidal thickness, choroidal vascularity index (CVI), and axial length (AL). After these measurements, participants were randomly assigned to wear either CMS spectacles with a 0.2 DOT pattern that covered the entire lens surface or clear +3.00D control spectacles (which acted as a positive control to induce myopic defocus). While wearing the spectacles, participants watched an age-appropriate video for 60 minutes. After 30 minutes and again after 60 minutes of viewing, the IOL Master and OCT examinations were repeated. On the second visit, participants wore spectacles that they had not used during the first visit, and the same measurements were repeated. Subsequently, the baseline OCT scans from both visits were exported, and sub-foveal choroidal thickness was measured using four different methods to evaluate the repeatability between methods. The most reliable measurement method was then used for further analysis. Chapter 7: This was a single-visit, prospective, randomized, subject-masked study. Participants were eligible if they had ±1.00D mean sphere prescription or less and they had no history of previous myopia control treatment. The logMAR visual acuity was measured, and ocular dominance was tested using the sighting method. Participants then wore a pair of plano CMS spectacles with a 0.2 DOT pattern that covered the entire lens surface and standard plano spectacles (control) in a randomized order and, after 5 minutes of adaptation to the lenses, ten open-field autorefraction measurements (Grand Seiko 5500) were taken for each eye, with the target at 6m and 40cm. Analysis was conducted on the mean auto-refraction to determine differences in the lag of accommodation (LOA) between lens types for the right eye and also for the dominant eye. Results: Chapters 3,4,5,6: A total of 30 participants were enrolled in the study and completed all assessments (17 females and 13 males). The mean age of the participants was 10.9 ± 1.7 years (median 11 years, ranging from 8 to 13 years). The mean refractive error was +0.35 ± 0.29 spherical equivalent refraction (SER). • Chapter 3: After one hour of wearing CMS spectacles, a two-way RMANOVA revealed a statistically significant reduction in AL (6µm) with p = 0.001. Similarly, a significant difference in CCT was observed, with p < 0.001 between baseline and both the 30-minute and 60-minute time points. Additionally, pairwise comparisons indicated a significance of p = 0.02 at the 30-minute time point between CMS and control spectacles. A similar reduction in AL (6µm) was noted with +3.00 control spectacles after one hour of wear. A significant difference (p < 0.001) was also observed for both ACD and LT with the +3.00D control spectacles at baseline versus 30 minutes and baseline versus 60 minutes. Furthermore, pairwise comparisons demonstrated significant differences between CMS and +3.00 control spectacles at the 30-minute (2.16 µm) time point for CCT and at both 30 (0.04 mm, 0.04 mm) and 60-minute (0.04 mm, 0.04 mm) time points for ACD and LT. • Chapter 4: When comparing the different methods of measurement for choroidal thickness, the manual method overestimated the choroidal thickness by 40 µm when compared to the semi-automated and automated AI-based method. Although repeatability between the measurements was satisfactory, the manual method did not show an acceptable Bland-Altman agreement when compared to the other three methods. However, a good agreement was observed between the semi-automated and the automated methods. • Chapters 5 & 6: The retinal thickness, choroidal thickness, and CVI were measured at all nine Early Treatment Diabetic Retinopathy Study (ETDRS) regions. In terms of choroidal thickness, only the outer inferior region of the retina showed a significant difference (p = 0.02) between the 30-minute and 60-minute marks when using CMS spectacles. Additionally, a significant difference was found between the CMS spectacles and the +3.0 control spectacles at the 30-minute point in 4 out of 9 macular regions. In contrast, no significant differences were found in any of the regions when using the +3.00D control spectacles. The retinal thickness and CVI did not exhibit any significant differences in any of the nine ETDRS regions for both CMS and +3.00D control spectacles. Chapter 7: A total of 30 participants (20 females and 10 males) with a mean age of 10.4 ± 2.8 (7 to 17) years completed the study. There was no significant difference in right eye mean LOA with CMS (+0.57 ± 0.39D) versus control spectacles (+0.62 ± 0.34D); Mann-Whitney U test, p = 0.64. For dominant eyes, LOA values were +0.60 ± 0.40D and +0.68 ± 0.33D with CMS and control spectacles, respectively (p = 0.25, not significant). Additionally, no significant difference was observed in mean LOA between males and females or between age groups (7-11 years vs 12-17 years) for either right or dominant eyes with CMS or control spectacles (all p = > 0.05). Conclusions: Chapter 3: Short-term wear of full-field myopia control CMS did not result in significant changes in anterior segment biometrics, retinal thickness, choroidal thickness, CVI and AL. There was only a minimal decrease of 3 µm in CCT after 60 minutes of wear; however, this minimal change was considered clinically insignificant. Chapter 4: This study concluded that manual, semi-automated, OCT inbuilt software and AI-based customized software methods are reproducible and repeatable. The manual method tends to overestimate the ChT and is time-consuming, as compared with both automated methods, which showed encouraging results for the OCT based TABS automated software. Chapters 5 & 6: Short-term exposure to full-field CMS did not lead to any notable changes in retinal or choroidal thickness. However, a significant difference in choroidal thickness was noted between the spectacles at the 30-minute time point, suggesting a rapid yet transient response. Further research with larger sample sizes and extended monitoring durations may be necessary to determine the clinical significance of these transient changes. Similarly, short-term exposure to CMS and +3.00D control spectacles did not lead to any notable change in CVI. Chapter 7: Full-field CMS had no significant effect on LOA compared to standard single-vision spectacle lenses, indicating no differential impact on accommodative response over the short period of lens wear tested.
Development of a biodegradable contact lens system for ocular drug delivery
(University of Waterloo, 2025-05-09) Garg, Piyush
Purpose: The aim of this thesis was to develop a biodegradable ocular drug delivery system (comprising contact lenses and conjunctival inserts), with the ability of controlled release of PVA using a physical cross linking method. Methods: In the first experimental chapter (Chapter 3), a commercially available 3D printer was modified and the 3D printing process with a gelatin methacrylate (GelMA) biomaterial ink was optimized. GelMA biomaterial ink was selected as a base material owing to its biocompatibility and demonstrated high levels of controllability. In the second experimental chapter (Chapter 4), the shape fidelity of the 3D printed contact lenses loaded with polyvinyl alcohol (PVA) as a therapeutic agent was evaluated. In the third experimental chapter (Chapter 5), a physical crosslinking strategy was evaluated as a potential modification to prolong the release of PVA from the GelMA network. In the final experimental chapter (Chapter 6), the degradation mechanism of GelMA-based conjunctival inserts in the presence of a matrix metallo proteinase enzyme (MMP9) is described, along with its correlation with the release of PVA. Results The results demonstrate that by tuning the printing conditions and ink parameters, soft biomaterials from a GelMA ink of higher shape fidelity and accuracy can be efficiently printed even on low-cost 3D printers. Moreover, a fine interplay between the dye concentration (CDye) and exposure time is key to effective polymerization and resolution, ensuring successful printing of the hydrogel biomaterials with higher structural integrity. It is further possible to add PVA to these lenses and the PVA release curves showed that about 1300 µg of PVA was released over the study duration of 24 hrs. PVA can act as a viscosity enhancer and protect corneal cells against dry eye related desiccation stress. These results were confirmed with the help of non-invasive keratograph break-up time measurements on a 3D printed eyeball model, where 1.4% (w/v) PVA solution displayed significantly higher tear break-up time compared to a control (p < 0.05). The release rate of PVA from these biomaterials can be controlled by applying short freeze thaw cycles, which induces formation of crystalline domains in the interpenetrating network. The appearance of endothermic peaks at 48 °C and 60 °C in differential scanning calorimetry (DSC) thermograms and 20°–2θ peaks in X-ray diffraction (XRD) patterns suggest the formation of these crystalline domains. The release profiles of the PVA containing hydrogels prove that crystalline domain formation could support sustained PVA release and control its initial burst release. The release profiles displayed highest linearity with the Korsmeyer–Peppas model (0.9944 < R² < 0.9952), indicating that these systems follow non-Fickian or anomalous transport. The results from this thesis highlight the versatility of 3D printing to fabricate GelMA-based conjunctival inserts. There are different factors that influence the MMP-mediated degradation of GelMA hydrogels, and that the degradation rate is a function of MMP9 enzyme concentration. The 3D printed GelMA/PVA inserts formed a semi-interpenetrating network. The results from the biodegradation study show that about 59.6% and 83.3% of the P-Gel-5% hydrogel was degraded at the end of 8 hrs and 12 hrs in the presence of 50 µg/ml MMP9 enzyme solution. Similarly, about 47.0%, 50.2% and 81.7% of the P-Gel-5% hydrogel was degraded at the end of 8 hrs, 12 hrs, and 24 hrs, respectively, in the presence of 25 µg/ml MMP9 enzyme solution. However, no degradation was observed in the control group incubated with PBS at the end of the study duration of 24 hrs. The PVA release graphs demonstrate that 222.7 ± 20.3 µg, 265.5 ± 27.1 µg and 242.7 ± 30.4 µg of PVA was released at 25 µg/ml, 50 µg/ml and 100 µg/ml MMP9 enzyme concentrations after 24 hrs. These results suggest that degradation rate of GelMA is a function of MMP9 enzyme concentration and the PVA release profiles of these inserts in the presence of different concentrations of MMP9 showed highest linearity with the Korsmeyer–Peppas model. Conclusions This thesis has investigated 3D printed CLs and conjunctival inserts for controlled ocular drug delivery. Several important findings have been reported, and the shortcomings have been discussed in this thesis. With the advancements in 3D printing, personalized ophthalmic devices fabricated from 3D printing could be a commercially viable option, but the cost and transparency need to be considered.
Efficacy of Vision Screenings in Waterloo Region
(University of Waterloo, 2025-01-22) McKinney, Marisa; Christian, Lisa; Irving, Elizabeth
Purpose: In 2018, the province of Ontario (Ontario) mandated a universal vision screening program for all senior kindergarten (SK) children (age 4-6 years). The purpose of the vision screening program is to detect children with risk factors for amblyopia, strabismus, and/or high refractive errors. The overarching aim of this thesis is to evaluate the effectiveness of Ontario’s universal vision screening program for SK children and how accurate the program is in identifying vision problems. These objectives are explored through two studies: parental adherence to vision screening recommendations survey, and investigation of the ability of Ontario’s vision screening program in identifying a SK child with a vision problem combined with determination of overall referral rates. Methods: All parents/guardians (parents) of SK students who participated in Ontario’s vision screening program in the Region of Waterloo (ROW) from October 2022 to December 2023 were invited to participate in the initial study to evaluate parental compliance to vision screening recommendations and barriers to seeking vision care. Following the first study, parents who reported taking their child to an optometrist following the vision screening were invited to participate in a follow-up study, evaluating the program sensitivity and specificity and overall screening accuracy. For the second study, the vision screening results were compared to the eye exam results, and all vision screening data (visual acuity, stereoacuity and autorefraction) for children who participated in the 2022-23 vision screening program were analyzed to determine the screening program’s overall referral rate and for all three screening tools. Results: 108 parents from 67 schools in the ROW responded to the survey to evaluate parental compliance in seeking vision services following the screening. The results of the survey found that over half (58/108, 54%) of the children screened were already under the care of an optometrist prior to the screening and less than half (48/108, 44%) of parents were prompted to obtain eye care, including 25% (27/108) who had already had a previous optometric examination. For the follow-up study that examined vision screening accuracy, 65 individuals participated. The vision screening program demonstrated a sensitivity of 0.935 and specificity of 0.406, producing a high rate of false positives (30%). Paired t-tests revealed significant differences in the accuracy of the vision screening tools compared with eye exam findings, particularly for refraction – sphere (OD: p = 0.005, OS: p < 0.001), cylinder (OD: p = < 0.001, OS: p < 0.001), and spherical equivalent (OD: p = 0.016, OS: p = 0.004). The retrospective review of the screening data included a total of 4837 vision screening results from 135 schools in ROW. The screening had an overall referral rate of 54% (2606/4837) and children were most commonly referred for autorefraction (43%; 2099) results followed by stereoacuity (31%; 1510). Conclusion: This analysis of Ontario's vision screening program for SK children in the ROW highlighted key findings. The program was effective at encouraging parents that received a refer to go to the optometrist (64%), though 31% of all parents misreported screening results, suggesting a need for clearer communication. The program showed high sensitivity (0.935) but low specificity (0.406), with a 54% referral rate and 30% false positives which may contribute to lack of public trust over time. Adjusting referral criteria based on evidence could reduce false positives.
Ocular Effects of Scleral Lens Wear on Dry Eye Patients
(University of Waterloo, 2024-11-14) Otchere, Heinz; Jones, Lyndon; Gorbet, Maud
Purpose: Dry eye disease (DED) is among the most complex ocular surface diseases to treat. Complaints of ocular discomfort and dryness are common in DED patients and in contact lens wearers. The use of SL to restore the integrity of the ocular surface in a more severe DED has become increasingly accepted among eye care practitioners. However, little is known about this treatment regimen and its impact on ocular surface in mild to moderate DED. Also, the potential impact of coated SL designs incorporating Hydra-PEG (polyethylene glycol) technology on ocular surface health has not yet been fully investigated. This thesis aimed to address this gap in knowledge and determine whether SL (uncoated or Hydra-PEG) could be used as a viable option for patients who are experiencing milder forms of DED. Over the course of the study, participants were asked to complete DE questionnaires; lens settling and vision, corneal thickness, osmolarity and matrix metalloproteinase 9 (MMP-9) in the pre-corneal tear film were investigated. The study also examined the relationship between the respective parameters and compared the two lens pairs. Methods and Materials: The study was a prospective, double-masked, randomized, dispensing, crossover clinical trial involving five visits, where 20 subjects with mild to moderate dry eye disease (DED) were enrolled. Eligibility of the participants was confirmed following the Tear Film and Ocular Society (TFOS) Diagnostic Report in the first visit: presence of symptoms using the Ocular Surface Disease Index (OSDI) and Standardized Patient Evaluation of Eye Dryness (SPEED) questionnaires (OSDI ≥ 13, SPEED ≥ 4), plus osmolarity values (> 308 mOsmol/L in either eye or interocular difference of > 8 mOsmol/L) and or a positive MMP-9 result (using InflammaDry® test kit) or both. The second visit involved randomization and dispensing of customized hydra-PEG coated or uncoated SL, where each pair of lenses were worn on a daily wear basis for four weeks. Prior to dispensing the lenses, high contrast (HCVA) and low contrast acuities (LCVA) were recorded. The central corneal clearance (CCC) was measured with VisanteTM OCT to determine lens settling over time. Two standard clinical questionnaires (contact lens impact on quality of life (CLIQ) and contact lens dry eye questionnaire 8 (CLDEQ-8)) and an internally developed wearing habit and subjective rating questionnaire were provided to subjects and completed. The third visit (after 4 weeks) involved follow-up of the first randomized SL, where the lenses were evaluated, and clinical measurements repeated. A wash-out period of at least 48 hours was allowed before dispensing (visit 4) and follow-up (visit 5) of the other pair of SL, using the same procedures, measurement protocols and visit schedule. The SL used in the study were Zen™ RC (Alden Optical, Bausch & Lomb, Lancaster, NY, USA) available in only two diameters (14.80 and 15.40 mm), with a central thickness of 250 µm. Results: Eighteen females and two males, mean age 29.10 ± 7.48 years, participated in the study. The overall OSDI and SPEED scores were 36.45 ± 17.08 and 12.50 ± 4.03 respectively. There was no significant difference in the CLIQ and CLDEQ-8 scores between uncoated and coated SL. In terms of wearing habit and subjective ratings, no statistically significant differences were observed in any of the parameters (wear time, dryness, burning, vision, and comfort). This suggests that the use of hydra-PEG coated SL did not show greater performance compared to the uncoated SL. The central corneal clearance (CCC) at the dispensing visit was 260 ± 40 (range: 200 - 300 µm) for both lens pairs. This significantly reduced to 190 ± 40 µm (lens settling: 70 ± 42 µm) for the uncoated SL and 200 ± 30 µm (lens settling: 70 ± 43 µm) for the coated SL at the follow-up visits, (all, p < 0.001). Comparing the CCC for the two lens pairs at the follow-up visits, no significant difference was observed, thus, the lens pairs settled at similar rates. In terms of HCVA and LCVA between the two lens pairs at both the dispensing and follow-up visits, there were no significant differences between them. Also, no significant correlations were found comparing the CCC with HCVA and LCVA of each lens pair at both visits. The CCT at the baseline and follow-up visits were: baseline: 560.55 ± 32.28 µm, post wear of uncoated SL: 557.65 ± 32.10 µm, and post wear of coated SL: 560.50 ± 34.02 µm. There were no significant differences for either lens type for central corneal thickness (CCT) at the baseline and follow-up visits (all, p > 0.05). Also, no significant correlations between CCC and CCT were observed at baseline or follow-up visits. These results demonstrated there were minimal corneal hypoxic effects when these SL were worn on a daily wear basis. For osmolarity measures, there was a statistically significant difference between the baseline and follow-up visit for the coated lenses (311.00 ± 14.86 vs 302.85 ± 7.96 mOsmol/L; p = 0.04). While this is statistically significant, the clinical relevance of this small difference remains questionable. Comparing the two lens pairs, no significant difference was found at all visits. The inflammaDry® test results indicated that 80 % of the participants tested positive for elevated MMP-9 at the baseline visit. There was a reduction in MMP-9 positive test results following the SL wear, however, there were no significant differences between the baseline and follow-up visits for each lens pair. Comparing the two lens pairs, no significant difference was observed. For either lens, no correlation was observed between osmolarity and MMP-9 test results. Conclusion: There is a potential for using SL to manage symptoms in subjects suffering from mild to moderate DED, as the overall wearing habit and subjective ratings showed > 70 % of lens tolerance among the study cohort. SL wear over the month of wear in this cohort induced little change to the cornea or conjunctival tissue. Furthermore, SL may appear to marginally reduce tear film osmolarity, however, further studies are needed to confirm this result and its impact on subjective dryness. The clinical phenomenon of lens settling needs further investigation, especially on its impact on conjunctival morphology. In this cohort of subjects of mild to moderate DED, the hydra-PEG coating technology did not show superior performance over the uncoated lens for any of the factors assessed. Keywords: dry eye disease. scleral contact lens, hydra-PEG, osmolarity, inflammadry, cornea
Extended Release of Ciprofloxacin from Commercial Silicone-Hydrogel and Conventional-Hydrogel Contact Lenses containing Vitamin E Diffusion Barriers
(University of Waterloo, 2024-08-13) Al Atrach, Mehdi; Jones, Lyndon; Phan, Chau-Minh
Abstract Purpose: Contact Lenses (CLs) are ophthalmic devices globally used by more than 140 million people to correct vision problems. To overcome the drawbacks of eye drops, drug-delivering CLs have been given much attention because they increase the bioavailability of ocular drugs, resulting in increasing efficacy and reducing potential side effects. These systems typically have a burst and rapid release. To address these concerns, this study aims to develop a contact lens-based ocular drug delivery system using vitamin E as a diffusion barrier to extend the release duration of ciprofloxacin. Methods: The purpose of the first experiment in the thesis (Chapter 3) was to develop and evaluate drug delivery contact lenses: Four commercial silicone hydrogel lenses (senofilcon A, lotrafilcon B, comfilcon A, and samfilcon A) and one conventional hydrogel lens (etafilcon A) were soaked for 24 hours in various concentrations of vitamin E dissolved in ethanol (0.0125 - 0.2 g/mL). The amount of vitamin E loaded was calculated by measuring the dry lens weight before and after vitamin E loading. The lenses were loaded with ciprofloxacin for 24 hours. The amount of ciprofloxacin loaded was determined using an extraction protocol. The drug release was evaluated in phosphate-buffered saline solution in an amber glass vial, at 37°C with shaking. The amount of ciprofloxacin released was measured using a UV-VIS spectrophotometer at 270 nm. The second experimental chapter (Chapter 4) aimed to evaluate the effect of ciprofloxacin loading duration on the uptake and release profiles of senofilcon A. This was done by applying the same method described in Chapter 3, except ciprofloxacin loading durations for senofilcon A were 24 hours and 7 days. Results: The data showed that there was a decrease in ciprofloxacin loading with increasing amounts of vitamin E loaded into the silicone hydrogel lenses. For each lens type, there was an optimal amount of vitamin E loaded that extended the release duration of the drug from 1 hour (without vitamin E) to as long as 16 hours. Senofilcon A with 0.025 g/mL vitamin E loaded exhibited the longest-sustained release for all lens types, achieving 16 hours of release. In contrast, vitamin E loaded into etafilcon A had no effect on the amount of drug loaded or the release duration. The data obtained in Chapter 4 showed no significant difference in the uptake and release profiles among the different loading durations (24 hours and 7 days), except in lenses with 0.025 and 0.05 g/mL vitamin E concentrations, which absorbed and released more drugs in the 7-day loading duration experiment. In addition, senofilcon A longest release duration (16 hours) achieved in chapter 3 did not further increase in chapter 4 after increasing the drug loading duration to 7 days. Conclusion: Vitamin E can be used as a diffusion barrier with commercial silicone hydrogel lenses to provide sustained release of ciprofloxacin. The results suggest that vitamin E may form blockages in channels within a silicone hydrogel lens material, thereby forcing a longer path for drugs to diffuse into and out of the lens material. There is an optimal amount of vitamin E that needs to be loaded to extend the release duration, and this is lens material dependent. Additionally, increasing the drug loading duration to 7 days was not enough to increase the drug-loaded amount, and subsequently the release duration specifically for senofilcon A loaded with 0.2 g/ml vitamin E concentration.
Colour Vision Deficiencies in the Digital Age: A Survey of User Experiences with Digital Displays
(University of Waterloo, 2024-07-09) Mazur, Sandra; Hovis, Jeffery
Introduction: Approximately 90% of dichromats and 67% of anomalous trichromats experience difficulty performing colour-related tasks daily (Steward & Cole, 1989). As technology becomes more prevalent, examining whether this condition impacts their use of digital displays is increasingly essential. Limited studies analyze the relationship between colour vision deficiencies (CVD) and digital displays. Mashige (2019) found that 63.2% of schoolchildren with CVD reported challenges when “working with computers,” suggesting that this condition may have some effect. Purpose: The purpose of this study is to examine the impact that congenital red-green CVD has on an individual’s interaction with digital displays in different areas of their daily life, such as “school,” “work/volunteering,” “gaming and eSports,” “driving/motorized vehicle,” and “travelling.” Materials and Method: An online survey was administered to people with CVD from Canada and the United States of America (USA). In addition to collecting demographic information and awareness of their CVD, information regarding difficulties carrying out colour-related tasks was collected. Because several software and filter options may improve performance on colour-related tasks, we asked whether they tried any and to rate their effectiveness. Results: A total of 381 individuals with CVD (280 males) completed the survey. Nearly 100% reported some difficulty with one of the tasks in most areas of life, individually, except for travelling (54.1%). For most tasks, there were no significant differences in the rankings based on sex and/or age group. Still, some tasks showed significant differences based on severity, primarily between mild and severe defects. Some examples included “colour-coded diagrams” at school, work/volunteering, and recreation/hobbies; “editing photos or other coloured images” at school, recreation/hobbies, and social media; and “reading coloured letters on various backgrounds” in gaming/eSports, online shopping/banking, and in-person shopping/banking. Nearly 65% of respondents reported making changes or implementing modifications to their displays, but there were 35% who did not. The most popular aid was “trial-and-error adjustments” of the colour and brightness of the display. Of the individuals who tried an aid, approximately 90% reported a modification to be at least a little effective, less than 3% reported at least one aid as ineffective, and only 25% rated the modifications as highly effective. There was no significant difference based on sex, age group, or severity for most modifications, except for passive aids (“coloured filters”) where youth found them more effective than adults. “Desktops/laptops,” “cell phones,” and “tablets” were the displays that people with CVD most frequently encountered difficulty and modified. The displays showed significant association with age group for some areas of life (work/volunteering, recreation/hobbies, gaming & eSports, and online shopping/banking) and modifications. This was probably due to the greater use of displays or differences in content, with youth having more problems with tablets and adults more with cell phones. Conclusion: Most respondents encountered some difficulty with at least one task, indicating that CVD had some effect on their ability to use digital displays. Although most respondents have tried some modifications to their displays, some respondents reported that at least one modification was ineffective and only 25% found an aid to be highly effective. Software developers should focus on making aids more accommodating and customizable to individual preferences.
New method to improve the diagnostic utility of OCTA images in retinal disease
(University of Waterloo, 2024-05-23) BHARDWAJ, RISHAV; BHARDWAJ, RISHAV
Purpose: Diagnosing medical images necessitates years of experience to ensure accurate diagnoses. However, the current workforce available for this task falls significantly short compared to the volume of images requiring assessment. This places a considerable burden on the medical system during diagnosis. Additionally, medical images often contain artifacts, further complicating and prolonging the diagnostic process. This thesis serves as a solution to expedite diagnosis by enhancing the image quality of Optical Coherence Tomography Angiography (OCTA) images, thereby alleviating the strain on the system. Aims: 1. Method 1 (Chapter 2): Removal of motion artifacts from OCTA images. It is one of the toughest artifacts to be removed from an image. 2. Method 2 (Chapter 3): Super-Resolution of OCTA image. Increasing the dimensions of the image and enhancing the quality to make diagnosis process efficient. Conclusion: This work allows the removal of motion artifacts from the OCTA image and then enhance the quality of the image using super-resolution. In chapter 4 we show that the scatterplots were used to compare the correlations of the most commonly used parameters, Foveal Avascular Zone (FAZ) area, perimeter, and circularity index, between before and after super-resolution at ×2 and ×3 magnification. A p-value < 0.05 was considered significant for all statistical tests. Thus, making the diagnosis process simpler and better for medical practitioners.
Advancements in ThermOcular image processing algorithms for precise ocular surface temperature analysis
(University of Waterloo, 2024-05-22) shahsavari, mohammad navid; Murphy, Paul; Wong, Alexander
In recent advancements in the field of Ocular Surface Temperature (OST) measurement, this thesis presents significant enhancements to the ThermOcular system, primarily focusing on its application in real-world clinical and diagnostic settings. The ThermOcular system, initially developed for precise OST measurement using infrared thermography, serves as a pivotal tool in measuring and tracking the OST in different components of the ocular surface. Recognizing the potential and limitations of the existing system, this work aims to introduce improvements that significantly elevate its diagnostic accuracy, user-independence, and overall applicability in clinical environments. In this thesis, a comprehensive strategy to refine the ThermOcular system is introduced, highlighting the simplification of the control point selection for clinicians using an innovative eye tag integration. This development is aimed at enhancing the registration process’s efficiency by reducing the need for manual input and the associated error margin prevalent in the prior methodology. Alongside, the thesis describes an enhancement of image segmentation accuracy, using state-of-the-art machine learning models trained on a comprehensive dataset prepared for this purpose. These models enable more precise classification of ocular components, crucial for accurate OST measurement. The thesis also addresses the challenge of artifacts due to the presence of eyelashes in thermal images and the effect of blinks on tracked OST, which previously compromised measurement accuracy. By developing and implementing algorithms for artifact detection and elimination, the thesis ensures that these common issues no longer compromise the reliability of OST assessments. This not only enhances measurement precision, but also contributes to the system’s robustness against varied conditions. In conclusion, the thesis encapsulates a significant advance in the domain of ocular health diagnostics using the ThermOcular system. By focusing on automation, accuracy, and artifact mitigation, this work contributes to the development of a more reliable, efficient, and clinically applicable system for OST measurement. The advancements highlighted in this thesis not only underscore the potential of infrared thermography in ocular diagnostics, but also pave the way for future research in this evolving field.
The Effect of Freezing on the Elution of PVA from Contact Lenses
(University of Waterloo, 2024-04-30) Shukla, Manish; Jones, Lyndon; Hui, Alex
Contact lenses are widely used, with over 140 million wearers globally. Wearing contact lenses can cause symptoms of discomfort and dryness, which affect nearly half of all wearers. To address this concern, this thesis explores the release of polyvinyl alcohol (PVA) from contact lenses, aiming to improve comfort through controlled elution. PVA forms a protective film when placed on the ocular surface and serves to reduce ocular discomfort. This research specifically studies the impact of freezing on PVA interaction with various contact lens materials and its subsequent release kinetics. This thesis hypothesizes that freezing enhances the hydrogen bonding of PVA to lens materials, enabling the formation of a surface layer on contact lenses and increasing PVA elution. To investigate this hypothesis, commercial lenses (Acuvue® Oasys – senofilcon A, DAILIES® AquaComfort PLUS® - nelfilcon A, 1-Day Acuvue® Moist® - etafilcon A) were soaked in 2.5% w/v high molecular weight PVA solutions at 37°C for 48 hours, followed by 1 hour at either room temperature or freezing at -80°C. The results demonstrate a significant (p<0.05) increase in the cumulative PVA release from nelfilcon A lenses after 24 hours following freezing at -80°C for one hour, with 55.07 ± 2.46 μg of high molecular weight PVA released in comparison to lenses kept at room temperature which showed 46.16 ± 6.94 μg of PVA release. In contrast to nelfilcon A, etafilcon A and senofilcon A did not show a significant (p>0.05) change in the amount of PVA released after freezing. Etafilcon A lenses released 17.03 ± 3.03 μg and 20.21 ± 2.51 μg (p>0.05), and senofilcon A showed 20.33 ± 6.60 μg and 24.14 ± 2.58 μg (p>0.05) at room temperature and after freezing at -80°C for one hour, respectively, suggesting that freezing enhances these iv effects only for nelfilcon A lenses. To further explore the impact of PVA with lenses, experiments with synthesized lenses (pHEMA and PVA loaded pHEMA) were performed, which demonstrated that the presence of PVA inside the lens significantly (p<0.05) impacts subsequent PVA loading and release and the freezing effect. The cumulative release of PVA over 24 hours from pHEMA lenses were 32.64 ± 5.48 μg and 36.25 ± 6.11 μg (p>0.05), at room temperature and after freezing at -80°C for one hour, respectively. PVA loaded pHEMA lenses, in contrast, showed a significant (p<0.05) increase in the cumulative PVA release over 24 hours after freezing, rising from 42.88 ± 4.96 μg to 47.39 ± 6.26 μg after one hour at -80°C. The study emphasizes the importance of PVA incorporation within contact lenses to observe a substantial impact on release after soaking or freezing. The findings suggest that the freezing technique has potential applications in enhancing the release of comfort agents such as PVA from contact lenses, especially those containing PVA internally. In conclusion, this research provides insights into optimizing contact lens design for improved comfort by utilizing PVA release. The demonstrated impact of freezing on nelfilcon A lenses indicates a promising avenue for enhancing the release of comfort agents.
Exploration of the Underlying Visual Perceptual and Cognitive Mechanisms of Dynamic Visual Acuity
(University of Waterloo, 2024-01-25) Hudecki, Heather; Dalton, Kristine
Purpose: Dynamic visual acuity (dynamic VA) is a complex, perceptual ability of the visual system that involves determining fine details of objects as they move across one’s field of view (1–4). Over the years, there has been increasing interest in dynamic VA because of its apparent relevance to everyday life, and its ability to account for motion, which static VA is unable to do. Dynamic VA has a crucial role in a variety of real-world situations and daily tasks that involve functioning in a dynamic environment, such as driving, piloting, crossing a busy intersection, and many ball sports (5–8). In addition, dynamic VA is an essential element involved in one’s ability to adapt to moving and changing environments (1). Although various research has been performed, dynamic VA as a visual function is not very well understood. This study was designed to investigate the potential underlying neurophysiological mechanisms that may be associated with dynamic VA. Methods: This study was an observational analysis of visual and cognitive function data collected from 130 participants. Participants were members of the University of Waterloo Department of Psychology Research Experiences Group (i.e., SONA), the University of Waterloo undergraduate and graduate community, the University of Waterloo Optometry Program, and the Kitchener-Waterloo Community. Five visual function tasks were studied including static visual acuity (static VA), horizontal and random dynamic VA, global motion (GM), global form (GF), and local motion (LM), along with two cognitive tasks, multiple object tracking (MOT) and the Stroop task. Static VA was measured first at each study visit to confirm participant eligibility, followed by horizontal and random motion dynamic VA (randomized order). After dynamic VA, the remaining visual and cognitive function tasks were measured in a randomized order. Static VA (LogMAR) was tested with an Early Treatment Diabetic Retinopathy Study (ETDRS) chart. Binocular dynamic VA (LogMAR; moV&, V&mp Vision Suite) was assessed using tumbling E optotypes moving in a horizontal (left to right) or unpredictable random motion. GM perception, and LM perception were assessed using random dot kinematograms (RDKs), GF perception was tested using Glass patterns, Stroop was assessed using word stimuli, and MOT was tested using randomly moving ball stimuli. Experimental effects, including the effects of participant age, participant gender, and testing order were examined for each task independently using one-way independent measures ANOVAs (age and visual function task order), and two-sample t-tests (gender and dynamic VA task order). Tukey post-hoc test was used to further evaluate any significant order effects found with the one-way independent measures ANOVAs. Correlation plots, matrices, and tables including Pearson correlation coefficients were calculated to examine the relationships between dynamic VA performance and the visual function tasks. Backwards stepwise regression analyses were conducted to determine which visual or cognitive function tasks were most predictive of dynamic VA performance. The correlation and regression analyses were performed separately for horizontal and random dynamic VA. Results: Highly significant correlations were found between horizontal dynamic VA and random dynamic VA (r = 0.49, p = 4.84e-9), static VA (r = 0.48, p = 6.35e-9), and LM (r = 0.32, p = 2.47e-4); a weak, significant correlation also noted with GM (r = 0.23, p =9.16e-3). Highly significant correlations with random dynamic VA were found with static VA (r = 0.46, p = 4.39e-8) and horizontal dynamic VA (r = 0.49, p = 4.84e-9); weak, significant correlations were found with LM (r =0.16, p = 6.43e-2), and GF (r = 0.15, p = 9.89e-2). Statistically significant predictors for horizontal dynamic VA were static VA (p = 6.09e-4), LM (p = 3.96e-2), and random dynamic VA (p = 1.20e-4) . GM (p = 0.139) was not a significant predictor of horizontal dynamic VA but still had a trend towards a positive relationship with the task. Static VA (p = 7.85e-4) and horizontal dynamic VA (p = 8.14e-5) were the only statically significant predictors of random dynamic VA, but there were also trends towards positive relationships between random dynamic VA and LM (p = 8.70e-2), and GF (p = 0.135). Additional analyses determined there to be no age or gender effects on any of the visual function tasks. A statistically significant order effect was present for GF (F(2, 127) = [4.92], p = 1.02e-3), but no other tasks. Conclusion: Horizontal dynamic VA appears to be most closely related to random dynamic VA, static VA, GM, and LM, suggesting the dorsal stream and V1 pathway may be the underlying neurophysiological pathways associated with processing horizontal dynamic VA. This is in comparison to random dynamic VA, which was most closely connected with horizontal dynamic VA, static VA, GF, and LM, suggesting the neuro pathways involved with random dynamic VA could be the ventral stream and V1 pathway. Further research is required to confirm and validate such neurophysiological mechanisms are associated with both horizontal and random dynamic VA.
Investigating the enhancement of visual cortex plasticity through non-invasive brain stimulation
(University of Waterloo, 2024-01-02) Chen, Xiaoxin; Thompson, Benjamin; Bobier, William
Purpose: (1) To investigate the effects of various non-invasive brain stimulation (NIBS) modalities, including high-frequency transcranial random noise stimulation (hf-tRNS), anodal transcranial direct current stimulation (a-tDCS), and repetitive transcranial magnetic stimulation (rTMS), on short-term ocular dominance plasticity in adults with normal vision; (2) To probe the neural mechanisms underlying short-term ocular dominance plasticity using NIBS techniques; (3) To explore the state-dependency of NIBS within the visual cortex; (4) To evaluate the efficacy of a novel ocular dominance test (the letter-polarity test) as a tool of measuring ocular dominance shifts following monocular deprivation (MD). Methods: Three studies using hf-tRNS, a-tDCS and rTMS were conducted. NIBS was delivered to V1 during MD. The primary outcome was ocular dominance shift, measured through two ocular dominance tests, a traditional binocular rivalry test and the letter-polarity test, before and after the interventions. Secondary outcomes included mixed percept durations and alternation rates as provided by the binocular rivalry test. The reliability of the letter-polarity test was evaluated in comparison to the binocular rivalry test through a comprehensive set of analyses. Results: (1) In three studies, short-term ocular dominance plasticity was observed as a shift in ocular dominance towards the deprived eye. (2) No significant effects of NIBS were observed on the primary and secondary outcome measures. (3) By comparing the effect of 120-minute MD and 30-minute MD, we observed a significantly smaller magnitude of ocular dominance shifts with 30-minute MD. (4) The reliability of the letter-polarity test was similar to that of the binocular rivalry test. Conclusions: These experiments suggest that the neural mechanisms underlying short-term ocular dominance plasticity in adults with normal vision may be more complex than a simple reduction in cortical inhibition. It may be necessary to reconsider the cortical site responsible for this plasticity and the neuromodulatory effects of NIBS on visual cortex activity. Our null findings of NIBS effects may also be explained by a different cortical activation state induced by MD. These findings provide valuable reference points for future studies investigating the enhancement of visual cortex plasticity.
Fabrication of microfluidic chip using 3D printing for ocular cell studies
(University of Waterloo, 2023-09-25) Ramasamy, Megala; Jones, Lyndon; Phan, Chau-Minh
Purpose: This thesis aimed to create a polydimethylsiloxane (PDMS) microfluidic chip utilizing low-cost commercial 3D printers and to integrate human corneal epithelial cells (HCEC) into the fabricated chip. Methods: The purpose of the first experimental chapter (Chapter 3) of this thesis was to develop PDMS devices from 3D printed moulds of two commercially available 3D printers: the Formlabs Form 3B+, which employs Stereolithography (SLA) technology, and the AnyCubic D2 DLP, which utilizes Digital Light Processing (DLP) technology. The fabrication of PDMS from 3D printed moulds can be achieved by introducing three simple post-processing steps: heating, sanding, and nail polish coating. A biomaterial coating was applied to the surfaces of the PDMS devices to render their surfaces hydrophilic. The second experimental chapter (Chapter 4) centred on incorporating HCEC into the PDMS device fabricated using the method described in Chapter 3. Results: Both 3D printers could generate optically clear PDMS devices with smaller channel dimensions of 100 µm, with faster print times and higher accuracy for the DLP 3D printer. Heating the 3D printed moulds produced fully cured PDMS chips with perfect channel edges. The sanding and nail polish coating of the mould produced optically transparent and smooth PDMS devices. Coating the PDMS surface with polydopamine (PDA) improved its surface wettability from 110° to 75°. On the PDA and collagen-coated device, HCEC exhibited significantly better growth than on the untreated PDMS device. HCEC cultured on these PDA/collagen-coated PDMS devices demonstrated 80% cell viability compared to conventional tissue culture plates. Conclusion: This study demonstrated that SLA and DLP printers can be used to produce PDMS microfluidic chips quickly and affordably. Notably, the DLP printer offered better accuracy and faster printing time than the SLA printer. The fabricated PDMS chips were transparent and capable of incorporating HCEC.
Advancing Hyperacuity for Vision Screening
(University of Waterloo, 2023-09-22) Mohammed, Abdul Rasheed; Lakshminarayanan, Vasudevan; Raahemifar, Kaamran
Introduction: The human visual system is extremely sensitive to certain spatial visual tasks. It can detect the subtle misalignment of closer objects to a degree of 2-5 arcseconds, which is smaller than the foveal cone diameter or spacing. This ability is referred to as hyperacuity, and one such visual task is the Vernier task, which involves misalignment detection of Vernier lines or dots. It is also called Vernier acuity and has a significant diagnostic value for screening various eye abnormalities. However, due to methodological and technical limitations, its utility was restricted to laboratory applications due to concerns over test reliability and testing time. I hypothesized that applying advanced psychophysical procedures, techniques, and modern technological interventions might improve the Vernier acuity testing standards for clinical consideration. Therefore, I attempted to address the challenges noticed in the literature by advancing the methodology and technicality to improve the Vernier acuity test efficiency for clinical application. Aims: ⸰ Experiment 1 (Chapter-2): To develop a software application and assess the Vernier acuity program performance, measurements, and stimuli characteristics. ⸰ Experiment 2 (Chapter-3): To enhance the Vernier acuity program efficiency, assess program performance and reliability for technical validation. ⸰ Experiment 3 (Chapter-4): To modify the Vernier acuity program for the visual field quantification (Hyperacuity perimetry) and assess reliability for technical validation. ⸰ Experiment 4 (Chapter-5): To develop a software application for the visual distortions quantification (Metamorphopsia) using Vernier acuity-based bisectional program and assess reliability for technical validation. Methods: This study was performed through two pilot studies: the first pilot study had five adult volunteers with the best corrected visual acuity of 20/20 vision in the right eye (tested right eye only) and included all the experiments from Chapter 2, whereas the second pilot study was carried out on 21 adult emmetrope (unaided 20/20 vision) volunteers (tested both eyes individually) and included all the experiments from Chapters-3, 4, and 5. I used PsychoPy3 to develop each software program. However, I employed two methods to provide the test results efficiently and reliably for clinical testing. I developed three software applications and could only perform technical validation because of the pandemic. ⸰ Experiment 1 (Chapter-2): I programmed a software program and employed a 3-Down, 1-Up adaptive staircase method and three alternative forced choices technique to quantify the Vernier acuity. The Vernier acuity was measured at seven vertical separations (gaps) to assess test performance. The initial testing was focused on determining test performance using stimuli shapes, followed by technical validation of the software application program and assessment of stimuli contrast for standardization. ⸰ Experiment 2 (Chapter-3): I adjusted the measurement parameters to improve test efficiency. I assessed the program performance from response accuracy, reaction time, and testing time, along with repeatability of measurements for technical validation of the Vernier acuity program. ⸰ Experiment 3 (Chapter-4): I modified the Vernier acuity program to quantify the hyperacuity perimetry in superior, inferior, nasal, and temporal visual fields. I assessed the repeatability of measurements for technical validation of this modified Vernier acuity program. ⸰ Experiment 4 (Chapter-5): I programmed a Vernier bisection program to quantify the metamorphopsia using a method of adjustment. The testing involved Vernier stimuli in two different orientations and referred to them as patterns (A and B), Pattern-A had a presentation of two vertical and horizontal line stimuli that are equally away from the center of the screen in either direction, whereas pattern B involved presentations of pattern-A at oblique angles to the screen center. Using both patterns, I measured the metamorphopsia in central 5 degrees and assessed the repeatability of the measurements and testing time for technical validation of the Vernier bisection program. Results: ⸰ Experiment 1 (Chapter-2): In the initial experiment, the line stimuli achieved comparable measurements to dot stimuli at most gap sizes except at 32 arcminutes of gap size. The test detected the lowest misalignment of 2 arcseconds at 2 arcminutes of gap size. The mean lowest acuity was below 8 arcseconds at 2 arcminutes, and the highest acuity was within an arcminute at 128 arcminutes. The negative contrast line stimuli were comparably precise to positive line stimuli at most gap sizes except at 16 arcminutes. ⸰ Experiment 2 (Chapter-3): The right eyes were repeatable at most of the gap sizes except for the 32 and 64 gap sizes, whereas the left eyes were repeatable at all gap sizes except 128. The right and left eye measurements were statistically the same at both visits. Since no difference was observed between the eyes, results from both eyes were compiled to assess the test performance and response accuracy. The Vernier acuity measured at 16, 8, 4, and 2 gap sizes were statistically repeatable, and the correlation was positive but weak. The response accuracy was estimated to be above 90% for mean correct responses, below 3% for mean incorrect responses, and about 5% for mean aligned responses through the gap sizes at both visits. The estimated reaction time was just below a second for mean correct responses, below 0.75 seconds for the mean incorrect responses, and about 2.5 seconds for the mean aligned responses. The test time was below 2 minutes at each gap size at both visits. ⸰ Experiment 3 (Chapter-4): The right eye hyperacuity perimetry results were repeatable in all four quadrants of 15 gap size, and the correlation was positive but weak in all quadrants except the superior visual field, where the correlation was negative and weak. Whereas for gap size 30, the results were repeatable in all quadrants except the inferior visual field, where the results were not repeatable. However, results from all the quadrants had a positive but weak correlation. The left eye hyperacuity perimetry results were repeatable in all quadrants of 15 gap size, except the nasal visual field, where the results were not repeatable. However, results from all the quadrants had a positive but weak correlation. For gap size 30, the results were repeatable in all four quadrants, and all quadrants had a positive but weak correlation. The results from both eyes showed no significant difference for a gap of 15 arcminutes. However, there was a substantial difference between the eyes only at the inferior field for a gap of 30 arcminutes. ⸰ Experiment 4 (Chapter-5): The right eye metamorphopsia results were repeatable in the central 5 degrees using a pattern A with a positive but weak correlation at all degrees except 5 and 1 degrees, where the correlation was negative and weak. Similarly, the results were repeatable in the central 5 degrees using a pattern B except for 5 degrees, and the correlation was positive but weak at all degrees except 3 and 2 degrees, where there was a negative and weak correlation. On the other hand, the left eye results were repeatable in the central 5 degrees using a pattern A with positive and moderate to strong correlations at all degrees. Similarly, the results were repeatable in the central 5 degrees using a pattern B except for 4 degrees, and the correlation was positive and moderate to strong at all degrees. There was no difference between the eyes for individual patterns at both visits. Conclusions: ⸰ Experiment 1 (Chapter-2): The developed software application program measured the Vernier acuity precisely using 3-down, 1-up, an adaptive staircase method, and the 3AFC technique. In addition, I standardized stimuli for shape and contrast to measure the Vernier acuity. The calculated results are precise and consistent with the previously reported data. Therefore, motivating to advance the test further for Vernier acuity testing. While performing the test, some areas for improvement were identified. By adjusting the necessary parameters, the test's efficiency can be enhanced. I plan to make those adjustments in the following pilot testing and perform technical validation. ⸰ Experiment 2 (Chapter-3): I adjusted the necessary parameters to improve the efficiency of the Vernier acuity testing. The results showed that the program is efficient, robust, and repeatable. The mean Vernier acuity measured at seven different gap sizes was consistent with previously reported data and comparable with pilot study 1 results. This cohort’s Vernier acuity measured at smaller gap sizes was highly dependable. The measurements were significantly repeatable at most gap sizes but were poorly dependable. Therefore, this program may need further modifications to achieve better reliable results for clinical testing. ⸰ Experiment 3 (Chapter-4): I modified the Vernier acuity program to quantify the Vernier acuity in eccentric 5 degrees of the macula (para-foveal area). The right eye results were repeatable for 15 arc minutes of gap size, whereas the left eye results were repeatable for the 30 arc minutes of gap size. However, both eyes had poor reliability at most of the gap sizes except the superior field of gap 30, where the reliability was moderate. This inconsistency between the eyes could be due to distinct reasons and therefore needs further investigations to address the underlying cause. ⸰ Experiment 4 (Chapter-5): I programmed a software application to quantify the metamorphopsia using a method of adjustment. The right eye results were repeatable at most gap sizes for both patterns. However, the measurements were poorly dependable at most gap sizes of both patterns. Similarly, the left eye results were repeatable at most gap sizes for both patterns. However, the measurements were poorly dependable at most gap sizes of both patterns, except at 3 degrees of pattern A and 5 and 2 degrees of pattern B, where the reliability was moderate. Further modifications in the program may provide better reliability for clinical testing.
Optometry Outreach in Indigenous Communities in British Columbia, Saskatchewan, and Manitoba
(University of Waterloo, 2023-08-31) Warren, Adrianna; Woo, Stanley; Irving, Elizabeth
Introduction: Inuit, Métis, and First Nations, the three main Indigenous groups within Canada, face disproportionate barriers to access for primary eye and vision care. Optometrists visit rural and remote Indigenous communities to provide outreach care to areas without a local optometrist; however, the approach is fragmented and not well represented. The purpose of this project is to assess the current state of outreach optometry within Indigenous communities by surveying optometrists who provide outreach care. Methods: In collaboration with the provincial optometry regulatory bodies, eligible participants were identified as optometrists who travel outside of their primary clinics to provide care within non-urban Indigenous communities. A questionnaire was developed through iterative stakeholder review for phase I of the study. The online questionnaire captured the delivery of care across one year (2022). The process of planning logistics, distances travelled, patient care provided and associated expenses were queried. A Semi-structured interview guide was developed for phase II of the study. One-on-one interviews expanded on questionnaire themes, providing insight into individual experiences. Data was collated through descriptive statistics and thematic coding for case and cross-case analysis. Results: The overall response rate was 50% (18/36) for the questionnaire and 30.5% (11/36) for the interview. Total questionnaire responses represent 96 outreach visits, 312.5 optometry clinic days, and 8,386 patient encounters across 64 communities in the three provinces. Optometrists coordinate with health center employees and school contacts to plan outreach visits, travelling primarily north to some of the most remote areas within each province. Overall Euclidean distances between participants primary clinic locations and communities visited ranged from 65 to 1405 kilometers (kms) (median: 438 kms). Costs per clinic day were highly variable ($174.44 - $3,800, mean: $765 per clinic day). Challenges reported were related to logistics, economic burden, and organizational challenges. Complementary enablers were identified, and recommendations are provided. Conclusions: This study is the first to provide visibility to the current state of outreach optometry care to Indigenous communities in British Columbia, Saskatchewan, and Manitoba. The process of planning outreach visits was variable for individual optometrists and between provinces. High variability in reported costs associated with outreach visits requires additional investigation. Multi-stakeholder collaboration to support optometry outreach programming would encourage outreach participation and improve services towards reducing eye and vision health inequity experienced by non-urban Indigenous populations. Acknowledgements: Project supported by Anonymous Philanthropic Foundation, Canadian Institute for Health Research Canadian Graduate Scholarship, and Canadian Optometric Education Trust Fund. No conflicts to declare.
The Phenotype of Tear Neutrophils and Their Role in Ocular Homeostasis and Inflammation
(University of Waterloo, 2023-07-31) Jin, Yutong; Gorbet, Maud; Jones, Lyndon
Introduction: Neutrophils (polymorphonuclear neutrophils, PMNs) are part of the innate immune system with potent killing mechanisms against pathogens. Although the anterior segment of the eye has a unique characteristic, immune privilege, a significant influx of PMNs has been detected after a prolonged eye closure at night, such as sleep. However, the functions and roles of tear PMNs in ocular homeostasis and complications remain largely unknown. The overall objectives of this thesis were to examine and compare the phenotype and functions of tear PMNs from healthy participants and participants with ocular allergy. Methods: Participants used a gentle eye wash method to collect tear PMNs from the ocular surface by washing their eyes with sterile phosphate buffer saline (PBS). • Study 1: Tear PMNs were either isolated from the eyewash by using the MACS-Column or EasySep cell separation system or reconcentrated by centrifugation. Stimulated (phorbol-12myristate-13-acetate (PMA), lipopolysaccharides (LPS) or N-Formylmethionyl-leucylphenylalanine (fMLP)) and unstimulated ROS production by both isolated and non-isolated tear PMNs were measured using luminol-enhanced chemiluminescence for 60 min. • Study 2: Tear PMNs were incubated with different medium conditions, Hank’s Balanced Salt Solution (HBSS) only, HBSS with lactoferrin, lysozyme, mucin, albumin, and IgG (ATS), and ATS without lactoferrin and lysozyme (MAI). Unstimulated or PMA-stimulated ROS production by tear PMNs was measured using luminol-enhanced chemiluminescence and flow cytometry with DCFH-DA. • Study 3: Tear leukocytes were collected at four different time points, after 2-hr and 7-hr of sleep at night, after 2-hr sleep during the day, and towards the end of the day (around 5 pm). After stimulation with fMLP, changes in the degranulation (lactoferrin, CD66b, CD63) and cell aging state (CD184) of tear PMNs were measured via flow cytometry. Neutrophil extracellular traps (NETs) were quantified by flow cytometry and visualized by microscopy following staining with myeloperoxidase, citrullinated histones, and CD15. • Study 4: Tear PMNs were collected from participants suffering from ocular allergy on two consecutive days, after a full night of sleep in the morning on Day 1 and at the end of the day, i.e., around 4:30 pm, on Day 2. Tear PMNs were either activated with fMLP or left unstimulated, followed by staining with antibodies against degranulation markers (CD66b and CD63), adhesion markers (CD11b and CD54), eosinophil marker (CD193), aging markers (CD184 and CD62L), as well as with the fluorescent probe DCFH-DA. The intensity of fluorescence was measured via flow cytometry. Results: • Study 1: Tear PMNs have a high level of constitutive/spontaneous ROS production even in the absence of any stimulus. However, tear PMNs failed to appropriately respond to LPS and fMLP, although they were able to produce ROS in response to PMA. Higher ROS generation was observed in isolated tear PMNs which may be caused by priming from the magnetic bead cell separation system. • Study 2: The presence of tear proteins significantly reduced the unstimulated and PMAstimulated ROS production by tear PMNs in HBSS and ATS. However, the findings on ROS production by PMA-stimulated PMNs incubated in MAI were different between the flow cytometry and chemiluminescence, suggesting that lactoferrin and lysozyme may have a greater impact on extracellular ROS production. • Study 3: Significantly more cells were collected from the nighttime compared to the daytime. 2hr EC night tear PMNs were less degranulated than 7hr EC night tear PMNs and possessed a higher activation ratio in response to fMLP. Furthermore, 7hr EC night tear PMNs exhibited hypersegmented nuclei and were prone to aggregation, when compared to 2hr EC night tear PMNs, suggesting an aged and activated phenotype. A significantly increased number of NETs were present in 7hr nocturnal closed-eye tear samples. • Study 4: There were significantly more tear PMNs collected from individuals with ocular allergy compared to healthy participants upon awakening. Tear PMNs from ocular allergy participants exhibited a less activated phenotype but a higher activation potential in response to fMLP compared to healthy participants, which was correlated with their younger maturation state. However, no significant difference in the production of ROS by tear PMNs between these two groups was observed. Conclusion: Tear PMNs become more aged and activated with increasing eye closure time at night, which can potentially aid in ocular surface surveillance. The presence of tear proteins may limit the ROS release by tear PMNs, thereby protecting the ocular environment from potential damage. However, in individuals suffering from ocular allergy, tear PMNs may be constantly recruited to the ocular surface, contributing to symptoms of ocular allergy and development of ocular complications associated with inflammation. This thesis identified some of the functionalities and potential roles of tear PMNs in maintaining ocular homeostasis and regulating inflammation. While further investigation is needed to comprehensively characterize the underlying mechanisms of tear PMNs involved in ocular inflammation, the current results may support the development of new therapeutical strategies to reduce ocular surface inflammation.

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