Optometry and Vision Science

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Acetic and Acrylic Acid Molecular Imprinted Model Silicone Hydrogel Materials for Ciprofloxacin-HCl Delivery
(Multidisciplinary Digital Publishing Institute, 2012-01-02) Hui, Alex; Sheardown, Heather; Jones, Lyndon W.
Contact lenses, as an alternative drug delivery vehicle for the eye compared to eye drops, are desirable due to potential advantages in dosing regimen, bioavailability and patient tolerance/compliance. The challenge has been to engineer and develop these materials to sustain drug delivery to the eye for a long period of time. In this study, model silicone hydrogel materials were created using a molecular imprinting strategy to deliver the antibiotic ciprofloxacin. Acetic and acrylic acid were used as the functional monomers, to interact with the ciprofloxacin template to efficiently create recognition cavities within the final polymerized material. Synthesized materials were loaded with 9.06 mM, 0.10 mM and 0.025 mM solutions of ciprofloxacin, and the release of ciprofloxacin into an artificial tear solution was monitored over time. The materials were shown to release for periods varying from 3 to 14 days, dependent on the loading solution, functional monomer concentration and functional monomer:template ratio, with materials with greater monomer:template ratio (8:1 and 16:1 imprinted) tending to release for longer periods of time. Materials with a lower monomer:template ratio (4:1 imprinted) tended to release comparatively greater amounts of ciprofloxacin into solution, but the release was somewhat shorter. The total amount of drug released from the imprinted materials was sufficient to reach levels relevant to inhibit the growth of common ocular isolates of bacteria. This work is one of the first to demonstrate the feasibility of molecular imprinting in model silicone hydrogel-type materials.
Adaptation to near addition lenses - Effect of AV/A ratio and age
(University of Waterloo, 2007-05-17T19:20:44Z) Sreenivasan, Vidhyapriya
AIM: The primary purpose of this thesis was to evaluate the pattern of changes to accommodation and phoria when pre-presbyopic individuals perform near work for 20 minutes with +2D lenses. In addition, the thesis also investigates the effect of the accommodative vergence cross-link (AV/A) and age on binocular adaptation to addition lenses. METHODS: Accommodation was measured using the PowerRefractor (Multichannel Systems, Germany) and phoria was measured using the modified Thorington Technique. Twenty four pre-presbyopic and emmetropic individuals (11 adults and 13 children) participated in the study. All participants fixated a near target at a distance of 33 cm for 20 minutes with +2D (lens condition) and without (no lens condition) +2D addition lenses. Binocular and monocular changes in accommodation and near phoria were measured at the outset and at 3, 6, 9, 15 and 20 minute intervals. RESULTS: Effect of +2D lenses on accommodation and phoria: The emmetropic adult participants exhibited lag of accommodation under the no lens condition (binocular: 0.51 ± 0.12D; monocular: 0.64 ± 0.15D) that were eliminated (under monocular viewing) and reversed (exceeded demand by 0.51 ± 0.11 D under binocular viewing condition) with the addition of +2D lenses. The near phoria showed a significant increase towards exophoria by 6 ± 0.56 ∆D upon introduction of +2D lenses. Sustained near viewing with +2 D lenses resulted in significant reduction of the binocular focus alone (not monocular focus) after 3 minutes of binocular viewing (magnitude of reduction: 0.24D; P<0.01). The exophoria also showed a concomitant reduction after 3 minutes of fixation at the near task (Magnitude of reduction: 3.6 ± 0.6 ∆D; P<0.001). The magnitude and rate of vergence adaptation, determined using an exponential function, was found to be 4.6 ± 0.21 ∆D and 2.12 minutes respectively for the emmetropic adult participants. Effect of age on vergence adaptation: A pattern of significant reduction in phoria and binocular focus similar to the adult participants was observed in young children. Analysis of the vergence adaptation curves in the two age groups did not show any significant difference in both the magnitude as well as the rate of phoria adaptation within the age range tested (Magnitude of adaptation - Adults: 4.65 ∆D; Children: 4.51 ∆D; P > 0.05; Time constants -Adults: 2.12 minutes: Children: 1.53 minutes, P > 0.05). Effect of AV/A ratio on vergence adaptation: The stimulus (St-AV/A) and the response AV/A (R-AV/A) ratios were determined and the participants were divided into two groups (low and high AV/A ratio) under both the conditions. The result indicated that, under both testing conditions (stimulus and response AV/A), the individuals with higher AV/A ratios demonstrated greater magnitudes of vergence adaptation than those individuals with lower ratios (Magnitude of adaptation: Low St-AV/A = 4.12 ∆D; Low R-AV/A= 4.25∆D; High St-AV/A = 4.88 ∆D; High R-AV/A = 4.65∆D; P<0.05) CONCLUSIONS: Introduction of near addition lenses initiated an increase in exophoria and convergence driven accommodation. Vergence adaptation occurred after 3 minutes of binocular viewing thus reducing exophoria and convergence driven accommodation. The magnitude and completeness of phoria adaptation were seen to depend on an individuals AV/A ratio with greater magnitude and incomplete adaptation observed in participants with higher AV/A ratios. Age, within the limits of the study did not appear to influence phoria adaptation with near addition lenses.
The adaptive elements of disparity vergence: Dynamics and directional asymmetries.
(University of Waterloo, 2018-04-24) Erkelens, Ian
Vergence eye movements alter the angle between the two visual axes, creating changes in binocular fixation distance. They are primarily stimulated by retinal image disparities, but can also be driven by inputs from ocular accommodation (accommodative-vergence) and perceived proximity (size) changes. Because of these diverse and complex sensory inputs, the neuro-motor substrates that sub-serve vergence control possess robust adaptive capabilities to manage the interactions with other oculomotor systems (accommodation). This adaptive plasticity in vergence allows for a high degree of precision in binocular alignment to be maintained throughout life in the face of constantly changing environmental demands. The precise alignment of each eyes’ fovea is a fundamental requirement for stereopsis and the perception of depth in 3 dimensions. In a significant portion of the ophthalmic clinical population, the adaptive capacities of vergence are reduced or dysfunctional, leading to difficulties focusing clearly and comfortably at near distances such as books, computer screens and other hand-held devices. Furthermore, new wearable technologies such as virtual and augmented reality increase the demand on the adaptive capacities of vergence by drastically altering the congruency of the sensory inputs to vergence. Currently, our understanding of the mechanisms that underlie this adaptive control and their behavioral limits are limited. This knowledge gap has led to conjecture in the literature regarding proper rehabilitative therapies for clinical dysfunctions of vergence control and in the optimal environmental design parameters that should provide comfortable and compelling user experiences in wearable technologies like VR and AR. The inward (convergence) and the outward (divergence) turning of the eyes in response to retinal disparities are controlled by two separate systems and demonstrate significant directional asymmetries in their reflexive response properties. In general, reflexive divergence responses tend to be slower and longer than their convergence counter-parts. It is unclear whether the adaptive mechanisms are influence by these reflexive asymmetries. It is also unknown whether similar directional differences exist in the different adaptive capacities possessed by vergence. The purpose of the following dissertation was to characterize the effects of stimulus direction on the adaptive behavior of disparity-driven vergence eye movements with an end goal aimed at improving rehabilitation therapies for clinical populations with vergence dysfunction and providing valuable insight for the design and future development of wearable technologies like virtual and augmented reality environments. A series of 4 experiments were conducted in order to characterize the effect of stimulus direction and the physiological limits of the adaptive behavior within the two-main disparity vergence motor controllers, fast-phasic and slow-tonic. In each study, binocular viewing conditions were dichoptic, which allowed retinal disparity to be altered while the accommodative and proximity cues were clamped. Such designs create incongruencies between the sensory stimuli to vergence and thus elicits a much stronger adaptive response for observation than would normally occur when viewing real-world objects. Eye movements were monitored binocularly with a video-based infrared eye-tracking system at 250Hz using the head-mounted EyeLink2 system. A total of 14 adult binocularly normal controls and 10 adult participants with dysfunctional convergence control (convergence insufficiency) were recruited for the main studies. 4 controls completed the first two studies, 10 additional controls completed the third and fourth studies while the 10 participants with convergence insufficiency completed the fourth study. The results of this dissertation make four significant contributions to the current scientific literature pertaining to vergence oculomotor control and plasticity. 1) Both fast-phasic and slow-tonic vergence controllers display directional asymmetries in their general behavior and adaptive responses. 2) Reflexive fast-phasic divergence responses in controls tend to saturate at lower disparity-stimulus amplitudes than convergence under specific viewing conditions. This saturation limit is defined when the primary vergence response amplitude and peak velocity are unable to increase when the stimulus amplitude increases, suggesting saturation in neural recruitment and firing rates. Saturated reflexive vergence responses instead recruit an increased response duration (neural firing time) in order to produce larger amplitude responses. 3) Saturation in the fast-phasic divergence mechanism leads to saturation in the speed slow-tonic vergence adaptation. The function of the underlying reflexive fast-phasic response was found to be associated with the adaptive behavior of the slow-tonic mechanism, suggesting one drives the other, which is consistent with model predictions. 4) Convergence responses from individuals with convergence insufficiency are generally indistinguishable from that of the slower divergence responses of controls. These impaired convergence responses lead to impairment of the adaptive mechanisms underlying each fast-phasic and slow-tonic controller. Clinically, these results suggest that rehabilitative therapies for vergence control dysfunctions should primarily target the performance of the fast-phasic reflexive vergence mechanism. This work also suggests that improvements in adaptive capacities of vergence, known to be the mechanism under-pinning symptom reduction in these patient populations, should follow when reflexive fast-phasic responses are normalized. In terms of wearable technology, the generally limited adaptive plasticity demonstrated within divergence responses when compared to convergence in controls, provides a behavioral explanation for the increase in symptoms of discomfort when viewing distant objects in virtual reality environments. Future investigations should seek to determine the effects of other disparity stimulus parameters, such as contrast and spatial frequency on the adaptive behaviors of both fast-phasic and slow-tonic mechanism. Finally, the cerebellum is known to be central to the adaptation of almost every motor system and yet its role in the different adaptive capacities of disparity-vergence control remain unclear. Future studies should aim to characterize these neural structures role in the different vergence oculomotor adaptive mechanisms described here.
Advancements in ThermOcular image processing algorithms for precise ocular surface temperature analysis
(University of Waterloo, 2024-05-22) shahsavari, mohammad navid
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.
Advancing Hyperacuity for Vision Screening
(University of Waterloo, 2023-09-22) Mohammed, Abdul Rasheed
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.
Agreement in dry eye management between optometrists and general practitioners in primary health care in the Netherlands
(Elsevier, 2015-04-18) Van Tilborg, Mirjam M.; Murphy, Paul J.; Evans, Katharine S.E.
Purpose: To investigate the agreement in dry eye care management between general practitioners (GPs) and optometrists in the Netherlands. Methods: A web-based survey was used to investigate the agreement in symptoms associated with dry eye, causes of developing dry eye, and investigative techniques used in practice, between GPs and optometrists. Additional questions surveyed knowledge of the latest research, and co-management of dry eye disease in primary healthcare. The anonymised questionnaire contained 16 forced-choice questions with Likert scales, and was sent to 1471 general medical practitioners and 870 registered optometrists. The response data was stored on an online database, and was converted directly to text format for analysis using SPSS 21 statistical analysis software. Results: 138 optometrists and 93 GPs responded to the survey (Cronbach α = 0.885, optometrists, and 0.833, GPs). Almost no agreement was found for all the questions: a statistically significant difference (Chi-square p < 0.0001) was found between the optometrists and GPs in the use of investigative techniques, associating symptoms, causes of dry eye (p > 0.0001), and dry eye symptoms, except for ‘burning sensation of the eye’ and ‘irritation of the eye’ as agreed symptoms, and agreement that dry eye is an age-related disease. Conclusions: As the optometrist and the GP are the gatekeepers for secondary healthcare, the fundamental differences in the methods of investigation and interpretation of dry eye-related symptoms, the possible cause of developing dry eye disease, and the therapy given by GPs and optometrists in the Netherlands, may have a significant impact on consistency of patient care.
Antifungal ocular drug delivery via contact lenses using a novel in vitro eye model
(University of Waterloo, 2016-04-21) Phan, Chau-Minh
Purpose: The purpose of this thesis was to evaluate the potential of contact lenses (CLs) as an antifungal drug delivery device, and to develop an in vitro eye model to test thereof. Methods: The first three chapters focused on developing a CL to function as a drug delivery device for natamycin, the only commercially available antifungal: • In the first experiment (Chapter 3), the in vitro uptake and release characteristics of natamycin from several commercially available CLs were evaluated • In the second experiment (Chapter 4), to improve the release characteristics of natamycin from contact lenses, an attempt was made to incorporate novel drug-encapsulated nanoparticles (Dex-b-PLA) within the CLs • In the third experiment (Chapter 5), an alternative strategy employing the incorporation of cyclodextrin (CDs) within the CL polymer matrix was evaluated as a potential modification to prolong the release of natamycin The second half of the thesis was aimed at developing a sophisticated in vitro ocular model capable of adequately measuring drug release from CLs: • In Chapter 6, the design of a novel in vitro eye model to simulate the physiological ocular environment was outlined • In Chapter 7, this model was used to evaluate the release of the antifungal fluconazole from commercially daily disposable CLs • In chapter 8, as an extension of the developed in vitro eye model, an agar eye model was developed to test the effects of natamycin and fluconazole-releasing CLs on Candida albicans Results Commercial CLs, after drug incubation with natamycin, will release the drug rapidly within the first half hour, followed by a plateau phase. However, when CL materials were loaded instead with natamycin encapsulated within novel Dex-b-PLA nanoparticles, the release duration was extended to 12 hours. Modifying the CL polymer with methacrylated CDs did not significantly improve drug release. On the contrary, high loading of CDs decreased overall drug delivery efficiency, likely resulting from unfavourable arrangements of the CDs within the polymer network. The developed ocular platform, termed Ocuflow, simulates physiological tear flow, tear volume, air exposure and mechanical wear. When this system was used to analyze the release of fluconazole from commercial CLs, the drug release was sustained for up to 24 hours. This observation significantly contrasts drug release observed in a vial, which typically follows a burst-plateau profile. When CLs releasing natamycin and fluconazole were tested on agar eye models that were inoculated with Candida albicans, the growth of the yeast was limited by natamycin-containing CLs. The cell morphology of the yeast also differed noticeably based on drug-lens combinations. Conclusions This thesis details potential strategies to develop novel CLs for antifungal ocular drug delivery. The Ocuflow system developed from this thesis is highly versatile; not only can it be used effectively to measure drug release from CLs, but it can also be applied to other in vitro analyses with CLs.
The appearance of hyper-reflective superficial epithelial cells observed using in vivo confocal microscopy
(University of Waterloo, 2010-01-22T19:54:48Z) Schneider, Simone
Purpose: Hyper-reflective superficial cells were an unexpected finding while examining the corneal epithelium using confocal microscopy (CM), during an MSc thesis conducted in 2006 at the University of Waterloo, Canada. The author1 suggested that the appearance of these hyper-reflective cells could be associated with solution induced corneal staining (SICS) that was also observed in those participants who had manifested these hyper-reflective cells. However, this hypothesis has not been reported in the literature. This thesis aimed to investigate variables that could possibly predict the appearance of hyper-reflective superficial cells. These investigated variables were the effect of: contact lenses, contact lens solutions, lens/solution combinations, long-term use of certain contact lenses and solutions, age, dry eye symptom, topical anaesthetics and sodium fluorescein. In addition to this, the normal superficial epithelium of controls was defined. Methods: CM images of the superficial epithelium were obtained during the various experiments from: 32 non-contact lens wearing participants, 18 post-menopausal participants symptomatic of dry eye and 18 post-menopausal age-matched asymptomatic women and 147 adapted soft contact lens wearers. For one experiment CM was performed with the contact lens in situ, making the use of a topical anaesthetic unnecessary. Superficial cellular appearance of CM images was graded using a custom grading scale. Hyper-reflective cells were counted. Corneal staining was assessed using sodium fluorescein. Results: Results obtained during the various experiments revealed that hyper-reflective cells predominately appeared with the use of a specific lens/solution combination. Also, the number of hyper-reflective cells peaked after two hours of lens wear. It was also shown that when hyper-reflective cells occurred during an experiment, not every participant who was exposed to that specific lens/solution combination manifested hyper-reflective cells. Also, a great deal of inter-subject variability in observed numbers of hyper-reflective cells was noted. Conclusion: In conclusion, this thesis established that the hyper-reflective cells that were observed by Harvey were reproducible and may co-occur with corneal staining induced by a specific lens/solution interaction
Application of a new grading scale for tear ferning in non-dry eye and dry eye subjects
(Elsevier, 2014-09-14) Masmali, Ali M.; AL-Qhtani, Sultan; Al-Gasham, Talha M.; El-Hiti, Gamal A.; Purslow, Christine; Murphy, Paul J.
Purpose: To apply the Masmali tear ferning (TF) grading scale on non-dry eye (NDE) and dry eye (DE) subjects to test the validity of the grading scale in practice, and to describe the grading scale range for NDE and DE. Method: Forty NDE subjects (20 males, 20 females) and 40 DE subjects (23 males, 17 females) ranging in age from 19 to 53 years (mean ± SD: 25.3 ± 5.5) with no other ocular disease, no contact lens wear, and not pregnant or breastfeeding were recruited. McMonnies scores were used for subject grouping. Phenol red thread (PRT) and slit-lamp test were used. A tear sample was collected from right eye, which was then dried to produce a ferning pattern, that was observed using a digital microscope, and graded. Results: Mean McMonnies, PRT and TF grade in NDE subjects were 7.1 ± 3.8, 27.4 ± 4.3 mm and 0.78 ± 0.40, respectively. Median McMonnies, PRT and TF grade in DE subjects were 16.5 ± 3.0, 9.0 ± 2.0 mm and 2.3 ± 1.48, respectively. In NDE subjects, grades 0.0–1.8 were observed (82.5% Grade 0.0–1.00). Grades 2.0–4.0 were observed in DE subjects (72.5% Grades 2.0–3.0). For all subjects, there were large correlations between TF grade and PRT (r = −0.79), PRT and McMonnies (r = −0.60), and TF and McMonnies (r = 0.73). Conclusions: The Masmali TF grading scale showed good validity in describing the TF patterns. Grades ≥2 can be classified as abnormal patterns. The TF test has the potential to be used in the clinic.
The Application of Digital Filters to Improve Visibility for People with Maculopathy
(University of Waterloo, 2007-09-28T20:13:35Z) Mei, Ming
Purpose: Previous studies have shown that some digital filters can enhance picture-image visibility for people with visual impairment. The ultimate purposes of this study are to determine the improvement of picture-image visibility for people with maculopathy using digital image enhancement, and to compare the enhancement effects of generic filters and custom-devised filters. The secondary interests are to investigate the effect of age and maculopathy on supra-threshold contrast matching and to investigate the spatial frequency characteristics of picture-images. Methods: In order to develop effective custom-devised filters, supra-threshold contrast matching and contrast thresholds for two age groups of subjects with normal vision (14 aged 20-50 years and 15 aged 51+ years) and three groups of people with maculopathy (13 with atrophic ARMD, 14 with exudative ARMD, and 8 with JMD) were measured. Amplitude spectrum at each spatial frequency and the slope of amplitude versus spatial frequency were measured to investigate the spatial frequency characteristics of single face and general scene images. To investigate the preference for filters, 7 generic filters and 4 custom-devised filters were applied to single faces and general scenes. The generic filters were high-pass/unsharp masking, contrast enhancement, Sobel edge enhancement, DoG convolution, DoG FFT, Peli’s adaptive enhancement, and a band-pass filter with equi-emphasis of spatial frequencies. The custom-devised filters were band-pass filters based on contrast sensitivity (CS) loss, contrast matching at 3.6% and 27.9%, and emphasis of the peak of the CS curve. Subjects with maculopathy were required to rate the visibility of each image with and without filtering. Nine subjects with maculopathy participated to assess the enhancement quantitatively during which the recognition of facial expression and details in general scenes was tested with and without filtering. Results: Contrast constancy was demonstrated in age-matched controls and people with maculopathy. Single faces were found to be of significantly lower average amplitude than the other groups of images. Eight filters were found to be effective in improving perceived visibility; contrast enhancement, Peli’s adaptive enhancement, DoG convolution, high-pass/unsharp masking, Sobel edge enhancement, band-pass based on 3.6% and 27.9% contrast matching and equi-emphasis band-pass filters. These filters specifically were found to be effective for one or more combinations of maculopathy type and image category. The most commonly preferred filters were the generic filters, contrast enhancement and Peli’s adaptive enhancement. The two highest rated filters for each subject significantly reduced the number of errors of facial expression and errors of recognition of detail within general scene images. Conclusions: The visual system adjusts to compensate for CS loss with aging and maculopathy. Single faces are unique in spatial frequency characteristics. Some generic and custom-devised filters are effective in enhancing image visibility. The custom-devised filters are not superior to the generic filters. Visibility enhancement can be assessed quantitatively.
Are high lags of accommodation in myopic children due to motor deficits?
(Elsevier, 2017-01) Labhishetty, Vivek; Bobier, William
Children with a progressing myopia exhibit an abnormal pattern of high accommodative lags coupled with high accommodative convergence (AC/A) and high accommodative adaptation. This is not predicted by the current models of accommodation and vergence. Reduced accommodative plant gain and reduced sensitivity to blur have been suggested as potential causes for this abnormal behavior. These etiologies were tested by altering parameters (sensory, controller and plant gains) in the Simulink model of accommodation. Predictions were then compared to the static and dynamic blur accommodation (BA) measures taken using a Badal optical system on 12 children (6 emmetropes and 6 myopes, 8–13 years) and 6 adults (20–35 years). Other critical parameters such as CA/C, AC/A, and accommodative adaptation were also measured. Usable BA responses were classified as either typical or atypical. Typical accommodation data confirmed the abnormal pattern of myopia along with an unchanged CA/C. Main sequence relationship remained invariant between myopic and nonmyopic children. An overall reduction was noted in the response dynamics such as peak velocity and acceleration with age. Neither a reduced plant gain nor reduced blur sensitivity could predict the abnormal accommodative behavior. A model adjustment reflecting a reduced accommodative sensory gain (ASG) coupled with an increased AC cross-link gain and reduced vergence adaptive gain does predict the empirical findings. Empirical measures also showed a greater frequency of errors in accommodative response generation (atypical responses) in both myopic and control children compared to adults.
Aspects of Corneal Fluorescein Staining
(University of Waterloo, 2019-04-25) Woods, Jill
PURPOSE Evaluating the cornea for epithelial fluorescein staining is a key element of the ocular examination of contact lens wearers and people with dry eye disease. It has long been viewed as a method of visualizing a break in the protective epithelial layer, the integrity of which is regarded as vital for protecting the eye and maintaining good vision. There has been very little reported on the typical staining presentation in dry eye. Understanding more about the distribution of epithelial staining in dry eye disease would be valuable to guide evaluation of a treatment’s physiological efficacy. This thesis aimed to determine whether the corneal staining of subjects with symptomatic dry eye presents in a specific distribution pattern Since 2002, the epithelial staining phenomenon of solution induced corneal staining (SICS) has been investigated. The cause of this staining has been suggested to be due to molecular adhesion rather than physiological damage, but the current evidence is equivocal. More investigation of this phenomenon is warranted to understand the process and the clinical significance of SICS. This thesis aimed to investigate the type, severity and pattern of staining that occurs in SICS, and assess the impact on epithelial cells using in-vivo confocal imaging. METHODS Chapter 2 described the CORE corneal staining scale., which uniquely reports the type and extent of the corneal staining on a scale of 0-100. This was the staining scale used to record the level of solution induced corneal staining in all the clinical trials featured in Chapters 5 and 6. Chapter 3 reported an experiment which was conducted to assess the agreement among fifteen observers who used this scale, in two grading sessions, to grade the corneal staining illustrated in 22 photographic images. Inter- and intra-observer agreement results were calculated. Chapter 4 presented a meta-analysis of the corneal staining observed in 368 subjects, across 13 studies, with symptoms of dry eye. For each subject the corneal zone of worst staining was recorded to analyse which region of the cornea most frequently exhibited the most severe staining. In Chapter 5, 20 subjects were exposed to a lens/solution combination, known to induce SICS, in both eyes for a two hour period. In phase one, one lens was rinsed thoroughly before being worn; in phase two, the eye itself was rinsed thoroughly post lens wear; in phase three, confocal microscopy was conducted on both eyes to look for hyper-reflective epithelial cells. In phases one and two, the epithelium was assessed for staining pre and post lens wear with and without fluorescein. Chapter 6 evaluated aspects of the staining data collected in several SICS-inducing studies. The frequency of the reported ‘donut’ pattern of staining was calculated, relative to a diffuse, pan-corneal staining pattern. Seven subjects were identified that had participated in three or more trials using the same SICS-inducing methodology. The data from these individuals were assessed to determine the repeatability of the level of induced corneal staining in these trials. RESULTS The CORE corneal staining scale agreement experiment, in Chapter 3, supported the benefit of training because the concordance of the naïve observer was markedly worse than the observers who had received prior training. The inter- and intra-observer agreement analyses provided valuable data which can be applied to the development a pictorial reference guide and better instructions. The Chapter 4 meta-analysis of the geographic distribution of corneal staining among subjects with symptomatic dry eye demonstrated that the greatest degree of staining was most frequently in the inferior zone. (52.5%) The zone affected least was determined to be the central zone (12.8%). In the SICS experiment of Chapter 5, rinsing the lens prior to wear and rinsing the eye post lens wear did not result in different staining to the non-rinsed condition. All eyes, irrespective of any rinsing treatment, presented with punctate staining over >84% corneal area. The SICS staining was visible before fluorescein was instilled as ‘white light staining’. Confocal images were obtained from 34 of the 40 eyes, and hyper-reflective cells were visible in 33 of those 34 eyes. The meta-analysis in Chapter 6 concluded that the ‘donut-ring’ staining pattern, which is often described as typical of SICS, was actually far less common than a diffuse pan-corneal staining presentation. When SICS responding eyes were defined as exhibiting staining of 10% extent in at least four of the five corneal zones, 89% were identified as presenting with the pan-corneal pattern i.e. all five zones met the 10% extent criteria. When the SICS definition was tightened to include only those with 50% extent in at least four zones, 76% of subjects still identified as the pan-corneal staining pattern. There was minimal evidence of SICS presenting with a repeatable degree of staining in the same individual across different clinical trials. CONCLUSIONS This thesis investigated several aspects of corneal epithelial fluorescein staining and the chapters have furthered understanding in this field in several ways. The CORE corneal staining scale provides valuable data regarding the percentage of the corneal affected by staining. The results of the Chapter 3 agreement experiment provide useful information for the next steps in the development of this scale which will create a valuable corneal staining assessment tool. The evidence that the most severe corneal staining in patients with symptoms of dry eye most often presents in the inferior zone is invaluable to the design of future clinical trials of dry eye treatments. It highlights the importance of specifically assessing this region and the value in targeting fluorescein staining improvements in this zone as a key outcome measure. SICS has been suggested to be due to adhesion between PHMB (or other care system components) and the epithelial cells. The experiment in Chapter 5 confirmed that rinsing the lens does not remove enough PHMB from the lens to prevent SICS, and rinsing the eye afterwards is not effective at removing the bound molecules from the epithelial cells because SICS is still evident post rinsing. The presence of ‘white light staining’ and hyper-reflective cells on in-vivo confocal microscopy indicate that there are changes to the epithelial cells even before the fluorescein is instilled into the eye. More investigation of changes at the cellular level are required to understand what is happening. The meta-analysis of SICS data was able to provide evidence that SICS most commonly presents as a diffuse punctate staining that affects the entire cornea presenting in a pan-corneal pattern, rather than presenting in the commonly described pattern of a donut-ring, which implies central zone sparing. The examination of SICS in seven subjects across several studies questions the repeatability of the SICS phenomenon. A targeted repeatability trial is required to conclusively answer this question.
Aspects of Dynamic Anterior Surface Aberrations
(University of Waterloo, 2014-01-07) Jayakumar, Varadharajan
Introduction: The measurement of tear film stability/regularity is very critical in the diagnosis of dry eye. The tear breakup time, which is used as a diagnostic tool in diagnosing dry eye, is very subjective in nature and variations among individual clinicians exists. The exact mechanism of the tear breakup is also unclear due to the involvement of so many other factors other than the tear film itself. As the prevalence of dry eye is increasing, the need for an objective technique which can be used universally to differentiate between dry eye and normal values increases. Studies have shown that aberrations can be used as an objective technique in diagnosing dry eye, as there is a direct involvement of the tear film in the optics of the eye. However, very few studies have studied the dynamic nature of the anterior surface using aberrations and suggested using dynamic surface aberrations as an objective measure of surface quality. Hence, a series of studies were conducted to understand the aberrations produced by the anterior surface of the eye (tear film and corneal surface) and to measure objectively the anterior surface quality using surface aberrometry. The objectives of each study chapter are as follows: Chapter 3 i): To obtain the noise associated with the instrument using a non-dynamic measuring surface, and ii) to design appropriate acquisition settings for the measurements with ocular surface. Chapter 4: To determine і) the spectral characteristics of the Placido disc light sources of two corneal analysers, іі) the thermal characteristic for a variety of inanimate objects, human ocular surface and the adnexa in the presence of Placido disc light source at normal working distance, and ііі) to compare the ocular surface aberrations obtained using both the corneal analysers Chapter 5: To determine i) the optimal method for acquisition with respect to normal physiological processes, by examining the blink regimen and head position that elicits the most consistent response over the largest region on repeated measurement; and iі) the largest region selected for analysis by investigating the effect on the individual and summary aberration metrics of the inclusion of non-measurement areas (i.e. where the Placido disc cannot be projected onto the cornea or contact lens). The proportion of non-measurement area that elicits a significantly different result will be determined. Chapter 6: To evaluate і) a new method of analyzing dynamic ocular surface aberrations using segmented liner regression, and іі) the inter-ocular characteristics of the dynamic ocular surface aberrations using the segmented linear regression. Methods: Chapter 3: The characteristics of the surface aberrometer and the noise associated with the measurements of surface aberrations were evaluated using a non-dynamic surface (model eye). Measurements were obtained in different frame rates and focus positions to evaluate the optimal acquisition technique. At each focus position, a set of three repeated measurements were obtained to analyse the repeatability of the measurements obtained using a surface aberrometer. Chapter 4: The spectral characteristics of the Placido disc light source were obtained by using a PR650 SpectraScan photometer and the thermal characteristics of the objects were obtained using THI-500 non-contact infrared thermometer. The surface aberration measurements were compared between the corneal analysers. The spectral measures were obtained from the light sources, whereas the thermal measures were obtained from three different surfaces and surface of the eye and adnexa of ten participants. The dynamic anterior surface aberrations were obtained after obtaining the thermal measurements from the surface of the eye. Chapter 5: Twelve participants were enrolled by screening twenty participants. Participants were screened with their habitual lenses for contact lens wettability and non-invasive tear breakup time (NITBUT) without contact lenses. The participants were enrolled according to the inclusion and exclusion criteria and categorized into normal and dry eye group for study visits. The measurements of NITBUT and surface aberrations were obtained with and without contact lenses, and study lens wettability were also obtained in two visits on consecutive days. The surface aberration measurements were obtained in natural and forced blinking condition and in two different head positions. All the measurements were randomized between eye and between instruments. Chapter 6: Seventeen non- symptomatic and non- contact lens participants were recruited in this study. NITBUT and dynamic anterior surface aberration measurements were obtained. The order of the measurements was randomized between the eyes. Two open intervals of at least 10 sec and a maximum of 15 sec were used in the analysis of segmented fit. The dynamic vertical prism coefficients and higher order aberrations were used for the analysis. Results: Chapter 3: i. Data acquisition at an inter-frame interval of 0.25s gave the least number of dropped frames across focus positions, therefore this is the preferred frame rate for data acquisition. ii. Data obtained in the initial ~15s reflects the focusing procedure and needs to be manually removed prior to analysis of tear dynamics. iii. Even in the optimal focus position there were significant (small) differences in the distributions between repeated measures. For this reason repeated samples have to be obtained where possible. iv. The green and red focus positions showed the most consistency within repeated measurements. The variability of the measurements was also more similar between the red and green focus positions than the blue focus positions, both at the extreme positions of defocus and with incremental defocus away from the optimal focus position. When obtaining the dynamic sampling of human ocular surface measurements, the optimal position of focus should be obtained at the blink such that as the tear film dissipates between blinks the measurements are obtained in the (relatively) red focus position. Chapter 4: i. CA200 is the preferred device because of the consistent luminance. ii. Although aberrations were not significantly different between devices, the HOA RMS were higher with the CA200 and, combined with different luminance and possible tear response, indicates the devices are not interchangeable. In both instruments, there was no indication that there was a thermal response induced by the power of the light source. Therefore, this aspect of the source does not likely contribute to any difference in the aberrations measured by the two devices Chapter 5: i. Obtain data in the straight-ahead position, as there is no significant increase in target size with head turn. ii. With the CA100F, the forced blink paradigm is preferred as this enables blink dynamics to be examined. With the CA200F, either forced or natural blink paradigms are interpretable for tear dynamics. iii. Differentiation between dry eye and normal groups was best determined with the slope of the RMS aberrations within a blink. iv. Differentiation between performance with and without a contact lens in the dry eye and normal groups was best determined by analysing the width of the confidence interval of the moving average. Chapter 6: i. The location breakpoints one and two are significantly different between eye, open eye interval and order of the measurements for both vertical prism and HOA RMS values. ii. The highest positive slope for the HOA RMS was, on average, higher in the second eye measured (p= 0.0407) and tended to occur later after the blink (p= 0.0676). iii. The location of breakpoint 2 is not significantly different from the NITBUT values (p>0.05), even though the correlation was found to be low and not significant. iv. The average HOA RMS for segmented fit parameter intervals of vertical prism was found to be higher in the second open eye interval compared to first open eye interval. Conclusion: From the results of each chapter, it was observed that choosing the blink paradigm is very important to obtain and analyse the dynamic anterior surface aberrations. Choosing a forced blink paradigm (chapter 5) was showed to be useful when the information regarding blink location were not available. The repeatability of the measurements using a non-dynamic surface (chapter 3) shows that the measurements of surface aberrations are repeatable and it is important to choose a criterion closer to the natural tear film dynamics to obtain more repeatable measurements of anterior surface aberrations (chapter 4, 5 and 6). It also shows that the three phased segmented linear regression techniques can be used to analyse the anterior surface aberrations. The segmented linear regression technique was able to differentiate different stages of the tear film and the location of the second breakpoint calculated using segmented regression was closer to the clinical values of tear breakup time, indicating a possible use of segmented linear regression as an objective measure of surface quality.
Assessment of Current and Next Generation of Colour Vision Tests for Occupational Use
(University of Waterloo, 2018-06-19) Almustanyir, Ali
Introduction: Individuals with congenital colour vision deficiencies are at a greater risk of making an error in colour judgment. Computerized colour vision tests are now available to screen for colour vision defects and quantify the severity of their defect. Purposes: The first experiment compared chromatic thresholds measured on different computerized colour vision tests for colour-normals (CVN) and colour vision defective (CVD) using a common scale. The next experiment evaluated whether dichromatic transformations of the Farnsworth D15 (F-D15) and the ColorDx D15 colors could predict the actual arrangements. The third study evaluated the within-session and between visits repeatability of each of the D15 tests. The last studies determined which one of the newer computer-based tests would replace the Holmes-Wright Type A Lantern (HWA), F-D15 and the CN Lantern. Lastly, the results of a short survey of how a colour vision deficiency affected their lives are presented. Methods: Sixty CVN subjects and 68 CVDs were tested with the Oculus HMC anomaloscope, Psuedoisochromatic tests (the Ishihara, Hardy, Rand, Rittler (4th ed), ColorDx PIP), computrized tests (CAD, Rabin Cone Contrast Test (RCCT), Cambridge Colour Vision Test (CCT), Landolt C Cone Contrast (LandC)), Lantern tests (HWA, CN Lantern), and arrangment tests (F-D15, ColorDx D15). Results: Discrimination ellipses measured in the CIE colour space with the CAD were significantly larger than the ellipse areas measured by CCT for CVNs, protans and deutans. For the tests that measure vector length, there were significant interactions between the three tests and the different subject groups. In general, the dichromatic transformation of the D15 tests provided reasonable predictions of the actual dichromatic arrangements. Both D15 tests studied showed that each test was highly repeatable within and between sessions. As expected, the ColorDx D15 had the highest level of agreement with the F-15, although it was not as challenging as the F-15. The LandC and CAD had significantly higher levels of agreement with the HWA compared with the other tests. Nearly all the CVD failed the CN Lantern test at 4.6m, but the number of errors decreased and the pass rate increased as the viewing distances of the CN lantern was shortened. At the 2.3 m distance, the agreement values for the HRR, ColorDx, and CAD were similar and considered as good. These agreement values decreased as the viewing distance decreased further. The results of the survey study showed that the percentage of dichromats who reported difficulties with colours was more than double of the percentage of anomalous trichromats, but lower than reported by other surveys. Conclusions: The difference between the CAD and CCT colour discrimination ellipses was likely a result of the different number and spacing of the chromatic vectors that were sampled in each program. The differences between the three tests that measured the vector length could be due to the luminance masking noise, monitor artifacts, different angular sizes, and psychophysiological procedures. The RCCT and LandC tests did not show a potential ceiling effect in estimating CVD thresholds, however, the LandC was preferred over the RCCT because it can measure chromatic threshold for CVN. The dichromatic predictions of the D15 tests suggest that this model may be useful in predicting the performance of dichromats on other colour-related tasks. The decrease in errors on the CN Lantern was likely due to the increase in brightness of the test lights with decreasing test distance. Although everyone with a colour vision defect will likely to fail the CN Lantern at 4.6 m, individuals who fail either version of the D15 will almost certainly fail the CN Lantern at 4.6 and 2.3m. A mild classification on the HRR and ColorDx PIP provides a reasonable prediction of who will pass the CN lantern at the shorter distances.
Assessment of ocular aberrations at scaled pupil size and reduced Shack-Hartmann spot number
(University of Waterloo, 2019-05-07) Ommani, Abbas
Wavefront aberrations describe the optical imperfections of the eye by measuring the complete refractive elements of the eye. However, the reliability of ocular aberration is uncertain under some challenges and issues. Ocular aberration is generally described in terms of Zernike polynomials. However, the Zernike polynomials are pupil size dependent, therefore, the aberration measured at a fixed pupil size cannot be used for another pupil size. One solution to this problem is to use pupil size scaling technique to scale up or down the aberration to a required pupil size; however, the validity of these techniques for clinical data is not available. To tackle this issue, validation of mathematical pupil size scaling formula by comparing the estimates of the Zernike coefficients with corresponding clinical measurements obtained at different pupil sizes is performed. The results show that the estimation of ocular wavefront aberration coefficients either scaling down from large to smaller pupils or scaling up from smaller to large pupils provides estimates that are not significantly different from clinically measured values. However, when scaling up to a larger pupil size, the estimates are more variable. These findings have implications for pupil scaling on an individual basis, such as in cases of refractive surgery or when using pupil scaling to examine a clinical cohort. Another challenge of an ocular aberration for clinical uses is when the spots on the Shack-Hartmann (SH) are missed due to the opacity of eye parameters or some other disease conditions. This issue is addressed by randomly deleting the number of spots from the SH images and comparing the results with the aberration of the original SH image without the missing spots. The results indicate that as high as 50 % of the SH spots can be deleted without affecting the estimation of spherical defocus within typical clinically acceptable limits of ±0.25D. The results are further examined with in vivo measurements of a human eye wearing a spectacle lens with various models of clustered missing spots to simulate loss that might occur with the disease. The findings of this study provide foundational data on measuring the ocular wavefront aberration when only a reduced number of SH spots are available.
The association between two quality of life measures for first time low vision device users
(University of Waterloo, 2006) Taji, Rana
Many individuals with impaired vision experience a decreased quality of life. Quality of life is defined as "the degree to which an individual enjoys the important possibilities of their life. " Vision rehabilitation outcomes primarily focus on the functional impacts of interventions, with less attention being paid to any associated psychosocial impacts. This study examines the relationship between measures of visual function status and psychosocial status in individuals acquiring low vision assistive devices for the first time. One hundred and twenty subjects were evaluated after purchasing their first low vision device from a University-based low vision clinic. The measures used were the National Eye Institute Visual Function Questionnaire (NEI-VFQ 25) and the Psychosocial Impact of Assistive Devices Scales (PIADS). The NEI-VFQ 25 measures the status of visual function, while PIADS is a device impact measure, which explores the psychosocial impact of devices on three domains: competence, adaptability, and self-esteem. This study determines the strength of association between these two measures at initial and follow-up administrations, and between each subsequent measure as a result of the time interval between administrations, in addition to assessing whether or not a change in stability for the measures occurred over time. Modest strengths of associations were anticipated and the short time interval was not expected to be a factor in change in stability of the measures. The expectation was that subjective reports of functional changes should have a moderate correlation with psychosocial impact.
The Association between Visual Attention and Body Movement-Controlled Video Games, Balance and Mobility
(University of Waterloo, 2018-09-21) Alghamdi, Mansour
Purpose: Interactive video virtual-reality body movement games such as Xbox Kinect may have potential for training visual attention and physical fitness concurrently in older adults in order to reduce the risk of falls. The purpose of this study was to investigate the relationships between performance in these types of games and visual attention, mobility and balance measures. This information is important before commencing any future randomised trial regarding the effectiveness of training visual attention and physical abilities with such games. Methods: This thesis includes two cross sectional studies of healthy adults, the first with an older (aged +65, n=50) and the second with a younger group (aged 18-40, n=50). Visual attention was measured with two different tests: useful field of view (UFV) and multiple object tracking (MOT). The useful field of view included two versions: a static (UFV-S) similar to those used in previous studies and a new dynamic version (UFV-D). For balance, body sway was measured with the Accugait portable force plate which records the center of pressure (CoP) under the feet. Body sway was measured in bi-pedal quiet stand test (QST) and one-legged stand (OLST). The medial-lateral (ML) and anterior-posterior (AP) CoP variability, ML and AP CoP maximum displacement, ML and AP CoP range and the cumulative path length were calculated. For mobility, the Five Meter Walk Test (5MWT) was used to observe the gait variability and walking speed. Stride and step lengths and widths were measured. The average and standard deviation of steps lengths (SL) and widths (SW) were calculated. Lastly, the velocity over the leg length (Vel-L) ratio was calculated to adjust participants’ speed according to their leg length. Performance in two pairs of games using the Microsoft™ Xbox® 360 Kinect™ interactive video game system was used in this study and were chosen based on the apparent visual attention demand. The first pair had apparently high visual attention demand and the second pair had apparently lower visual attention demand. All the games had a physical component (exercise games). Results: In both experiments, measures of visual attention (UFV and MOT) showed correlations with Xbox Kinect game scores that appeared to have a high visual attention demand, while there was minimal or no significant association with the games of apparent low visual attention demand. Static useful field of view (UFV-S) was the most common visual attention test that showed correlations with the high visual demand. Dynamic useful field of view (UFV-D) had a role for the younger group, but not in the older adults. Multiple regression models showed that scores for some of the games with high visual attention demand were predicted by visual attention measures. Age was also a predictor in the older group. The games with low visual attention demand were found to be mainly predicted by balance and/or mobility measures. There were correlations between some visual attention tests and balance and mobility in the older adult group which remained after adjustment for other factors. However, visual attention measures were not found to be predictors for any balance and mobility measures in the multiple regression models for either group. Significant correlations were found between Xbox Kinect games and some measures of balance and mobility. Conclusion: The results in this study suggest that there are relationships between visual attention, balance, mobility and Xbox Kinect games performance. Thus, playing these games may train visual attention and improve the balance and mobility over time. However, the choice of the game is important as some are more associated with physical ability and others with attention. Playing Xbox Kinect games may have a potential for training visual attention as well as physical abilities, but the game chosen is critical and a battery of games may be most effective.
Atomic force microscopy analysis of the effect of plasma treatment on gas permeable contact lens surface topography
(Elsevier, 2019-02-23) Gill, Felicity; Purslow, Christine; Murphy, Paul J.
Purpose: Using atomic force microscopy (AFM) to investigate anterior surface topography (AST) in worn and unworn, plasma surface-treated (PST) and untreated (UT) gas permeable (GP) lenses, and influence of surface topography on in vivo comfort. Methods: GP lens AST evaluated with AFM in tapping mode, using an uncoated, 40 nm symmetric tip (sampling frequency: 300 kHz), at five randomised locations, over a 100μm2 area, to produce mean average roughness (Ra) and root mean square (RMS) values for each sample. Four unworn lenses (two PST, two UT) were examined (Quasar/Boston EO material). Twenty worn lenses (ten PST, ten UT) of same design and material as unworn lenses collected after 3 months lens wear. General wearing comfort reported by visual analogue scale (VAS) at 3 months visit. For sample preparation, two worn UT GP lenses were divided into four segments; each segment underwent a different lens rinse and drying method. Results: Unworn: UT lenses had significantly higher mean RMS and Ra values compared to PST (Mann-Whitney, p < 0.05). Worn: UT Median RMS values were significantly higher than PST (Mann-Whitney, p < 0.05). Comfort: no correlation found between general comfort and RMS or Ra scores. Sample preparation: Method 4 (purified, distilled water rinse/nitrogen gas dry) produced optimum median RMS and Ra values. Conclusions: Unworn PST GP lenses had lower Ra and RMS values compared with unworn UT GP lenses. After 3 months wear, PST lenses had smoother surface topographies than UT lenses. No relationship was found between surface topography and lens wear comfort. Sample preparation protocol directly impacts AFM results.
Atomic force microscopy and Langmuir–Blodgett monolayer technique to assess contact lens deposits and human meibum extracts
(Elsevier, 2015-07) Hagedorn, Sarah; Drolle, Elizabeth; Lorentz, Holly; Srinivasan, Sruthi; Leonenko, Zoya; Jones, Lyndon W.
Purpose: The purpose of this exploratory study was to investigate the differences in meibomian gland secretions, contact lens (CL) lipid extracts, and CL surface topography between participants with and without meibomian gland dysfunction (MGD). Methods: Meibum study: Meibum was collected from all participants and studied via Langmuir–Blodgett (LB) deposition with subsequent Atomic Force Microscopy (AFM) visualization and surface roughness analysis. CL Study: Participants with and without MGD wore both etafilcon A and balafilcon A CLs in two different phases. CL lipid deposits were extracted and analyzed using pressure-area isotherms with the LB trough and CL surface topographies and roughness values were visualized using AFM. Results: Meibum study: Non-MGD participant meibum samples showed larger, circular aggregates with lower surface roughness, whereas meibum samples from participants with MGD showed more lipid aggregates, greater size variability and higher surface roughness. CL Study: Worn CLs from participants with MGD had a few large tear film deposits with lower surface roughness, whereas non-MGD participant-worn lenses had many small lens deposits with higher surface roughness. Balafilcon A pore depths were shallower in MGD participant worn lenses when compared to non-MGD participant lenses. Isotherms of CL lipid extracts from MGD and non-MGD participants showed a seamless rise in surface pressure as area decreased; however, extracts from the two different lens materials produced different isotherms. Conclusions: MGD and non-MGD participant-worn CL deposition were found to differ in type, amount, and pattern of lens deposits. Lipids from MGD participants deposited irregularly whereas lipids from non-MGD participants showed more uniformity.
Attentional Factors Underlying Binocular Vision Loss in Amblyopia
(University of Waterloo, 2022-01-13) Chow, Amy
Amblyopia is a neurodevelopmental disorder of vision that results from abnormal visual experience during early development. In addition to significant vision loss in one eye, individuals with amblyopia experience binocular dysfunction, difficulty with visuomotor coordination and attentional deficits. A key component of the vision loss associated with amblyopia is strong, chronic suppression of the amblyopic eye. Clinically, suppression remains challenging to treat, and is a key obstacle to rehabilitating visual function in amblyopia. This thesis examines whether suppressed visual information from the amblyopic eye remains available for processing within the brain and whether higher-order attentional processing is affected in amblyopia. Emerging evidence suggests that attentional mechanisms may contribute to interocular suppression and vision loss in amblyopia. Across four experiments, the findings from this thesis provide several major insights about amblyopia. Visual information seen only by a suppressed amblyopic eye retains a presence within the brain that may subsequently be used for attentional processing. Attentional mechanisms in amblyopia were found to be intact to some extent and thus can be engaged. Orienting visual attention was effective for targets seen by a partially suppressed amblyopic eye and even for complex face cues. Selective attentional tracking by the amblyopic eye was intact in anisometropic amblyopia but was impaired for strabismic amblyopia. Additionally, the process of attentional disengagement and re-engagement may be impaired during amblyopic eye viewing. Overall, these results demonstrate that the amblyopic eye continues to influence visual perception despite being suppressed under normal viewing conditions. As a result, appropriate refractive correction of the amblyopic eye should be clinically prescribed to optimize image quality for binocular combination. Furthermore, amblyopia may affect how visual attention is allocated between the eyes, providing a therapeutic target to guide future rehabilitative efforts.

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