Optometry and Vision Science

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This is the collection for the University of Waterloo's School of Optometry and Vision Science.

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Ocular Discomfort Upon Tear Drying
(University of Waterloo, 2003) Varikooty, Jalaiah
Purpose: Assess the relationship between tear film drying and sensation between blinks. Methods: MATLAB sampled a slitlamp video camera, a potentiometer and a microphone while subjects kept one eye open for as long as possible. 23 subjects rated the intensity of the ocular sensation while video and voice data were collected simultaneously. The tear drying on the cornea was measured. Results: The sensation was triphasic. Two linear functions described the latter 2 parts of the data (r ≥ 0. 95). The correlation between TBUT and the elbow in the time-discomfort function was 0. 72. Extent of tear film drying was linearly correlated to time (median correlation = 0. 88). The correlation between the discomfort elbow and image elbow was 0. 93 with single data pair for each subject. Analysis of sensation characteristics showed significant differences between itching and burning for both intensity and time (p = 0. 03 and p = 0. 02 respectively). Conclusions: Simultaneous recording of ocular surface appearance, discomfort intensity and attributes of sensation provide novel information about the development of discomfort during ocular surface drying. The rapid increase in discomfort proceeding blinking has been quantified and the relationship between the time course of drying and discomfort is elucidated.
A Study of Saccade Dynamics and Adaptation in Athletes and Non Athletes
(University of Waterloo, 2004) Babu, Raiju Jacob
Purpose: The aim of the study was to delineate differences in saccade characteristics between a population of athletes and non athletes. Aspects specifically investigated were latency, accuracy, peak velocity, and gain adaptation of saccades using both increasing and decreasing paradigms. Methods: A sample of 28 athletes (varsity badminton and squash players) and 18 non athletes (< 3 hour/week in sports) were studied. Eye movements were recorded at 120Hz using a video based eye tracker (ELMAR 2020). Each subject participated in 2 sessions on separate days. Baseline saccade responses to dot stimuli were measured in both sessions (stimulus size: 5-25 deg). The first session involved a gain decreasing paradigm, induced by displacing the stimulus backwards by 3 degrees from the initial target step (12 deg) for 500 trials. In the 2nd session a gain increase was induced by displacing the stimuli by 3 degrees in the forward direction. The latency and accuracy were calculated from the baseline. The asymptotic peak velocity was calculated from the main sequence (amplitude vs. peak velocity). The amplitude gains, calculated from the adaptation phase, were averaged for every 100 saccade responses. The averaged gains were normalized with respect to the baseline, fitted with a 3rd order polynomial, and differentiated to obtain the rate of change. Differences between the groups were compared using a regression analysis. Results: There were no significant differences in latency, accuracy, and asymptotic peak velocity between athletes and non athletes. No significant differences were seen between the two groups in the magnitude of saccadic adaptation, both for decreasing (- 15% in both groups) and increasing (athletes + 7% and non athletes + 5%) paradigms. However, athletes showed a significantly faster rate of adaptation for the gain increasing paradigm (F = 17. 96[3,6]; p = 0. 002). A significant difference was not observed in the rate of adaptation for the gain decreasing adaptation (F = 0. 856[3,6]; p = 0. 512). Conclusions: The study showed that the athletes do not respond better in terms of reaction time or accuracy of saccades. The significant difference in the rate of change of adaptation between the groups shows that online modification of saccades in the positive direction, although not greater in magnitude, occurs quicker in athletes than non athletes.
Study of the dynamic interactions between vergence and accommodation
(University of Waterloo, 2005) Suryakumar, Rajaraman
Introduction: Accommodation (change in ocular focus) and Vergence (change in ocular alignment) are two ocular motor systems that interact with each other to provide clear single binocular vision. While retinal blur drives accommodation as a reflex, retinal disparity changes accommodative position through the convergence-accommodation (or simply vergence-accommodation, VA) cross-link. Similarly, while retinal disparity primarily drives the vergence system, a change in retinal blur alters vergence through the accommodative-convergence (AC) cross-link. Although much information is known on the individual response dynamics of blur accommodation and disparity vergence, very little is known about the cross-linkages AC and VA. VA represents the unique situation where a stimulus to vergence (retinal disparity) drives a change in accommodation. When these dynamic measures are compared to those of vergence and blur accommodation a better understanding of the critical or rate limiting step within the system of vergence and accommodation can be determined. Accordingly, the purpose of this thesis was to determine the response dynamics of vergence driven accommodation (VA) and compare the response parameters to simultaneous measures of disparity vergence and blur driven accommodation.

Methods: A disparity stimulus generator (DSG) was modified to allow step stimulus demands of disparity to be created on a 0. 2 cpd non-accommodative difference of Gaussian target. Retinal disparity of different step amplitude demands were created as an ON / OFF paradigm and projected on a stereo monitor set at a distance of 1. 2m. Two experiments were conducted. The first experiment investigated the first order properties of VA in comparison to similar measures of blur driven accommodation (BA). The second study aimed at comparing the first order and second order dynamics of disparity vergence, VA and BA.

In the first experiment, stimulus measures of vergence, vergence-accommodation and BA were studied. Six normal young adult subjects participated in the study. Accommodation was measured continuously at 25Hz with the commercially available PowerRefractor (Multichannel systems, Germany). A Badal optical system was designed and accommodative response to step stimulus demands were measured. VA and BA measures obtained from the PowerRefractor were matched and plotted as main sequences (amplitude vs. peak velocity). Peak velocities between the two responses were compared using two-way analysis of variance (ANOVA) with Bonferroni post-tests.

In the second experiment, the response dynamics of vergence, vergence-accommodation, and blur accommodation were assessed and compared on 6 young adult subjects. Eye position was measured continuously by a stereo eye tracker at a sampling rate of 120Hz. A high speed photorefractor (sampling = 60Hz) was custom designed and synchronized with a stereo eye tracker to allow simultaneous measurement of vergence and VA. Monocular blur driven accommodation measures were also obtained with the Badal optometer and the high speed photorefractor (sampling = 75Hz). VA, BA and disparity vergence responses were analyzed and temporal parameters like latency, amplitude, duration, time to peak velocity, peak acceleration, duration of acceleration, and skewness were calculated. Main sequence plots (response amplitude vs. peak velocity) were generated and compared between disparity ON and disparity OFF. The dynamic measures of VA were compared to the measures of monocular blur driven accommodation. All comparisons were done using a two-way ANOVA with Bonferroni post-tests.

Results:
Study 1: The results showed that response amplitude of VA during disparity ON and disparity OFF paradigms was linearly related to the peak velocity for an amplitude range of 0. 5 to 2. 5 D (Disparity ON: peak velocity of vergence-accommodation = 0. 812 * amplitude + 1. 564, R² = 0. 452, p<0. 0001 and Disparity OFF: peak velocity of vergence-accommodation = 1. 699* amplitude ? 0. 234, R² = 0. 86, p <0. 0001). The rate of change of peak velocity as a function of response magnitude was lower for VA during disparity ON compared to VA during disparity OFF. BA responses also showed amplitude dependent dynamic properties (Accommodation peak velocity = 1. 593 * amplitude - 0. 008, R² = 0. 84, p<0. 001; Dis-accommodation peak velocity = 1. 646 * amplitude - 0. 036, R² = 0. 77, p<0. 001). There was no statistical difference in the velocity of accommodation and dis-accommodation.

Study 2: When amplitudes were matched, disparity vergence response during disparity ON and disparity OFF had similar main sequence relationships. The mean values for the stimulus and response VA/V ratios were similar (0. 13±0. 05 D/Δ and 0. 15±0. 09 D/Δ respectively). All the temporal parameters of vergence-accommodation were similar during disparity ON and disparity OFF paradigms. When blur accommodation and vergence-accommodation measures were compared, all the first order and second order temporal parameters in the response were similar between the two systems. Also, disparity vergence exhibited significantly greater peak velocity and peak acceleration compared to two accommodation responses. The results also confirmed that the velocity of accommodation and dis-accommodation showed a statistically significant linear relationship as a function of amplitude for the range of amplitudes tested (Accommodation, y = 2. 55x + 0. 65, R² = 0. 55, p<0. 0001; Dis-accommodation, y = 2. 66x + 0. 50, R²=0. 65, p<0. 0001).

Conclusions: The dynamic properties of VA are amplitude dependent. Although initial results from study 1 suggested that VA may be slower during disparity ON, the results from study 2 using the high speed photorefractor and an improved analysis procedure showed that VA responses were equally fast between disparity ON (convergence) and disparity OFF (divergence). All temporal properties of VA were independent of vergence type (convergence/divergence). VA and BA have similar dynamic properties in humans suggesting that they may controlled by a common neural pathway or limited by the plant. Also, when compared to accommodation responses, disparity vergence exhibited greater velocities and accelerations reflecting the differences in the magnitude of neural innervation and plant mechanics between the two systems. The study also confirmed amplitude dependent response dynamics of blur driven accommodation and dis-accommodation.
Lysozyme Deposition Studies on Silicone Hydrogel Contact Lens Materials
(University of Waterloo, 2005) Nagapatnam Subbaraman, Lakshman
Over 60 proteins have been detected in the tear film and among these lysozyme has attracted the greatest attention. Several techniques for elucidating the identity, quantity and conformation of lysozyme deposited on soft contact lenses have been developed. Lysozyme also deposits on the newly introduced silicone hydrogel (SH) lens materials, but in extremely low levels compared to conventional hydrogel lenses. Hence, a major analytical complication with the study of the SH contact lens materials relates to the minute quantity of deposited lysozyme. The first project of this thesis involved the development of a method whereby lysozyme mass extracted from SH lens materials would be preserved over time and would be compatible with an optimized Western blotting procedure. This methodological development was incorporated into a clinical study (CLENS-100® and Silicone Hydrogels ? CLASH study) wherein the difference in the degree of total protein, the difference in lysozyme deposition and activity recovered from lotrafilcon A SH lens material when subjects used surfactant containing rewetting drops (CLENS-100®) versus control saline was investigated. The remaining experiments were in vitro experiments wherein the lenses were doped in artificial lysozyme solution containing ¹²⁵I-labeled lysozyme. These experiments were performed to gain insight into the kinetics of lysozyme deposition on SH lens materials and also the efficacy of a reagent in extracting lysozyme from SH lens materials. A protocol was developed whereby the percentage loss of lysozyme mass found on lotrafilcon A SH lenses was reduced from approximately 33% to <1% (p<0. 001), following extraction and resuspension. The results from the CLASH study demonstrated that when subjects used a surfactant containing rewetting drop instead of a control saline drop total protein deposition (1. 2±0. 7 µg/lens versus 1. 9±0. 8 µg/lens, p<0. 001), lysozyme deposition (0. 7±0. 5 µg/lens versus 1. 1±0. 7 µg/lens, p<0. 001) and percentage lysozyme denaturation (76±10% versus 85±7%, p=0. 002) were all reduced. The results from the kinetics study demonstrated that lysozyme accumulated rapidly on etafilcon A lenses (1 hr, 98±8 µg/lens), reached a maximum on the 7th day (1386±21 µg/lens) and then reached a plateau (p=NS). Lysozyme accumulation on FDA Group II and SH lenses continued to increase across all time periods, with no plateau being observed (p<0. 001). The results from the extraction efficiency study showed that 0. 2% trifluoroacetic acid/ acetonitrile was 98. 3±1. 1% and 91. 4±1. 4% efficient in extracting lysozyme deposited on etafilcon A and galyfilcon lenses, while the lysozyme extraction efficiency was 66. 3±5. 3 % and 56. 7±3. 8% for lotrafilcon A and balafilcon lens materials (p<0. 001). The results from these studies re-emphasize that novel SH lens materials are highly resistant to protein deposition and demonstrate high levels of biocompatibility.
Monocular Adaptation of Vestibulo-Ocular Reflex (VOR)
(University of Waterloo, 2005) Sehizadeh, Mina
Purpose: This study asks whether active horizontal angular Vestibulo-Ocular Reflex (VOR) gain is capable of monocular adaptation after 4 hours of wearing 10 dioptres (D) of induced anisometropia in healthy human adults. Method: The participants (average age 28 years) wore a contact lenses/spectacles combination for 4 hours. The power of the spectacle was +5. 00D (magnified images 8. 65%) in front of the right eye and ?5. 00D (minified images 5. 48%) for the left eye, while the power of the contact lenses was equal to the subjects? habitual correction, summed with the opposite power of the spectacle lens. Eye and head position data was collected in complete darkness, in one-minute trials before adaptation and every 30 minutes for 2 hours after adaptation. Eye and head position data obtained using a video-based eye tracking system, was analyzed offline using Fast Fourier Transform in MATHCADTM 11. 1 software to calculate VOR gain. The VOR gain was compared between the right eyes and left eyes for the trials before and after adaptation. Results: In the first post-adaptation trial, a significant decrease in VOR gain (? 6%) occurred in the left eye in response to the miniaturizing lens. The right eye VOR gain did not show a significant change in the first post-adaptation trial (?2% decrease). During the remaining trials in the 2 hour follow-up time, both eyes showed a significant decrease compared to the baseline trial. This might indicate habituation of the VOR from repeated testing, or fatigue. Conclusion: There was monocular adaptation of VOR in response to the combined contact lenses/spectacles, but it was not complete and it was not as we expected. However, trying different amounts of anisometropia in one or two directions, a longer adaptation period (more than 4 hours) or monitoring the gain for more than 2 hours after adaptation with a longer separation between trials, might show different results.
In vitro and ex vivo wettability of hydrogel contact lenses
(University of Waterloo, 2006) Rogers, Ronan
The wettability of contact lenses has become an area of intense research, with the belief that the more "hydrophilic" or wettable the lens surface is, the more comfortable the lens may be, as the posterior surface of the eyelid will move more smoothly over it, hence increasing comfort.

There are many ways to assess the wettability of a given material, namely sessile drop,¹ captive bubble ² or Wilhelmy plate. ³ This thesis used the sessile drop method to determine the surface wettability of various hydrogel contact lens materials, by measuring the advancing contact angle made between the lens surface and a pre-determined volume of HPLC-grade water. This was followed by measuring the surface wettability following periods in which the lens materials were soaked in various contact lens care regimens. Further studies determined wettability of lens materials after various periods of in-eye wear and finally a study was undertaken to evaluate if a novel biological technique could be used to differentiate proteins that deposit on hydrogel lens materials that may affect wettability and cause discomfort.

A variety of hydrogel lenses, taken directly from their packaging and after soaking in various care regimens, were analyzed to determine their sessile drop advancing contact angles, in vitro. These studies indicated that poly-2-hydroxyethylmethacrylate (pHEMA)-based lenses are inherently more wettable than silicone-based lenses, unless they have a surface treatment that completely covers the hydrophobic siloxane groups. Additionally, certain combinations of lens materials and care regimens produce inherently more wettable surfaces when measured in vitro.

Suitable methods to assess contact lens wettability ex vivo, or after subjects had worn lenses for set periods of time, were developed. It was determined that using latex gloves to remove lenses had no impact upon the lens surface wettability and that rinsing of the lens surface after removal from the eye was required to determine the wettability of the underlying polymer.

The final wettability studies involved an analysis of various lens materials from clinical studies conducted within the Centre for Contact Lens Research (CCLR). These studies investigated differences in wettability between silicone hydrogel lenses manufactured from differing polymers and variations in ex vivo wettability of several combinations of lens materials and solutions, worn for varying periods of time.

A novel method to investigate proteins extracted from lenses using 2D-Difference in Gel Electrophoresis (DIGE) found that this technique could be used to analyze proteins extracted from contact lenses. The data obtained showed that there was no difference between a group of subjects who were symptomatic of lens-induced dryness or a control group, and that care solutions had a minimal influence on the pattern of deposition seen.

The overall conclusion of these studies is that hydrogel lens wettability is affected by the polymer composition and that care regimen components can modify the surface wettability.
Lipid Deposition on Hydrogel Contact Lenses
(University of Waterloo, 2006) Lorentz, Holly
The primary objective of this study was to quantify and characterise lipid deposition on soft (hydrogel) contact lenses, particularly those containing siloxane components. Studies involving a variety of in vitro doping and in vivo worn contact lenses were undertaken, in which lipid deposition was analyzed by either TLC or HPLC. Specific experiments were completed to optimize a method to extract the lipid from the lens materials, to compare the total lipid deposition on nine different hydrogel lenses and to analyze the effect that lipid deposition had on wettability. A method for extracting lipid from contact lenses using 2:1 chloroform: methanol was developed. This study also showed that siloxane-containing contact lens materials differ in the degree to which they deposit lipid, which is dependent upon their chemical composition. Small differences in lipid deposition that occur due to using variations in cleaning regimens were not identifiable through TLC, and required more sophisticated analysis using HPLC. Contact lens material wettability was found to be influenced by in vitro lipid deposition. Specifically, conventional hydrogels and plasma surface-treated silicone-hydrogel materials experienced enhanced wettability with lipid deposition. Reverse-phase HPLC techniques were able to quantify lipid deposits with increased sensitivity and accuracy. From the HPLC studies it was found that contact lens material, concentration of the lipid doping solution, and the composition of the lipid doping solution in in vitro deposition studies influenced the ultimate amount and composition of lipid deposits. In vivo HPLC studies showed that the final lipid deposition pattern was influenced by the interaction between the composition of the tear film and the various silicone hydrogel contact lens materials. In conclusion, HPLC analysis methods were more sensitive and quantitative than TLC. Lipid deposition was ultimately influenced by the concentration and composition of the lipid in the tear film and the contact lens material. Contact lens wettability was influenced by the presence and deposition of lipid onto the contact lens surfaces. Finally, this reverse-phase HPLC lipid analysis protocol was not the most sensitive, robust, or accurate. In the future, other methods of analysis should be explored.
Central Visual Field Assessment in Late Stage Glaucoma
(University of Waterloo, 2006) Balian, Carmen
Glaucoma is defined as a progressive optic neuropathy, characterized by loss of visual function and often associated with high intra-ocular pressure. Testing the patients' visual function with Standard Automated Perimetry (SAP) is currently the clinical standard for detecting glaucomatous visual field loss. A new test algorithm using the Frequency Doubling illusion has been introduced on the Matrix perimeter (Humphrey Matrix; Carl Zeiss Meditech, Dublin CA) that measures the central 10° using a 2°x 2° square flickering stimulus. This stimulus has the theoretical advantage of being both a large target, with good repeatability, and being perceptually selective, by preferentially stimulating the magnocellular projecting ganglion cells.

The purpose of this thesis was to determine the within-technique, between-visits repeatability and the within-visit, between-technique comparison of several techniques available to measure the central 10° visual field in patients with late stage glaucoma. In particular, to examine test-retest variability and compare sensitivity threshold values, visual field indices, and total and pattern deviation probability maps among the following techniques: Full Threshold SAP 10-2 size III (SAP III), Full Threshold SAP size V (SAP V), SITA SAP 10-2 size III (SS III), and Matrix 10-2 2° stimulus (M2).

Forty nine patients with advanced glaucomatous visual field defects attended 3 visits. During each visit, 1 eye was examined with each of the 4 techniques mentioned above. Data from the first visit was discarded to eliminate bias that may occur from the learning effect. Coefficient of Repeatability values of SAP III, SAP V, SS III, and M2 were calculated to be 10. 33, 9. 00, 9. 90, and 12. 04%dB respectively, relative to the average difference in threshold estimates between visits. M2 had the most uniform test-retest characteristics across the full range of sensitivities; however the 90% confidence interval was the widest of all techniques in the normal to near normal range (24 to 38dB). M2 showed the greatest defects in both total and pattern deviation probability plots. Threshold estimates of SAP III and SS III were shown to be similar and slightly more variable than SAP V. M2 showed greater defects than SAP III in both total and pattern deviation probability plots. Compared to SAP III and SS, M2 estimated sensitivity as less severe. Estimates of 20 dB and above on M2 were estimated at approximately 30 dB with SAP V. In the moderate to abnormal sensitivity range, Matrix estimated points to be shallower than that estimated by SAP V.

This thesis showed that test-retest variability of the SAP techniques decreased with increasing sensitivity whereas; variability was constant throughout the dynamic range for M2 and smaller in the moderate to severe range. However M2 was worst in the normal to near-normal sensitivity range. This suggests that M2, compared to all SAP techniques, will be disadvantaged for the detection of early visual field loss but better positioned to repeatably detect and follow moderate to severe loss in the central 10° of patients with late stage glaucoma.
In Vivo Imaging of Corneal Conditions using Optical Coherence Tomography
(University of Waterloo, 2006) Haque, Sameena
Purposes: To use optical coherence tomography (OCT) to image and quantify the effect of various corneal conditions, in terms of corneal, stromal and epithelial thickness, and light backscatter. To assess the changes caused by overnight orthokeratology (Corneal Refractive Therapy; CRT^TM) lens wear, keratoconus and laser in-situ keratomileusis (LASIK) refractive surgery, each of which may lead to topographical alterations in corneal thickness either by temporary moulding, degeneration, or permanent laser ablation, respectively.

Methods: Topographical thickness of the cornea was measured using OCT in all studies. The CRT^TM studies investigated myopic and hyperopic treatment, throughout the day. The myopic studies followed lens wear over a 4 week period, which was extended to 12 months, and investigated the thickness changes produced by two lenses of different oxygen transmissibility. CRT^TM for hyperopia (CRTH^TM) was evaluated after a single night of lens wear.

In the investigation of keratoconus, OCT corneal thickness values were compared to those obtained from Orbscan II (ORB) and ultrasound pachymetry (UP). A new fixation device was constructed to aid in the measurement of topographical corneal and epithelial thickness along 8 directions of gaze. Pachymetry maps were produced for the normal non-lens wearing cornea, and compared with the rigid gas permeable (RGP) lens wearing cornea and the keratoconic cornea.

Thickness changes prior to, and following LASIK were measured and monitored throughout six months. Myopic and hyperopic correction was investigated individually, as the laser ablation profiles differ for each type of procedure. The LASIK flap interface was also evaluated by using light backscatter data to monitor healing.

Results: Following immediate lens removal after myopic CRT^TM, the central cornea swelled less than the periphery, with corneal swelling recovering to baseline levels within 3 hours. The central epithelium decreased and mid-peripheral epithelium increased in thickness, with a more gradual recovery throughout the day. There also seemed to be an adaptation effect on the cornea and epithelium, showing a reduced amount of change by the end of the 4 week study period. The thickness changes did not alter dramatically during the 12 month extended study. In comparing the two lens materials used for myopic CRT^TM (Dk/t 91 vs. 47), there were differences in stromal swelling, but no differences in the central epithelial thinning caused by lens wear. There was a statistically insignificant asymmetry in mid-peripheral epithelial thickening between eyes, with the lens of lower Dk causing the greater amount of thickening. Hyperopic CRT^TM produced a greater increase in central stromal and central epithelial thickness than the mid-periphery. Once again, the stroma recovered faster than the epithelium, which remained significantly thicker centrally for at least six hours following lens removal.

Global pachymetry measurements of the normal cornea and epithelium found the periphery to be thicker than the centre. The superior cornea and epithelium was thicker than the inferior. In the measurement of the keratoconic cornea, OCT and ORB correlated well in corneal thickness values. UP measured greater values of corneal thickness. The keratoconic epithelium was thinner than normal, and more so over the apex of the cone than at the centre. The location of the cone was most commonly found in the inferior temporal region. Central epithelial thickness was thinner in keratoconics than in RGP lens wearers, which in turn was thinner than in non-lens wearers.

Following LASIK surgery for both myopia and hyperopia, the topographical OCT thickness profiles showed stromal thinning in the areas of ablation. The central myopic cornea showed slight regression at 6 months. During early recovery, epithelial thickness increased centrally in hyperopes and mid-peripherally in myopes. By the end of the 6 month study, mid-peripheral epithelial thickness was greater than the centre in both groups of subjects. The light backscatter profiles after LASIK showed a greater increase in backscatter on the anterior side of the flap interface (nearer the epithelium), than the posterior side (in the mid-stroma) during healing. The flap interface was difficult to locate in the OCT images at 6 months.

Conclusion: All the CRT^TM lenses used in this project produced more corneal swelling than that seen normally overnight without lens wear. In order for these lenses to be worn safely for long periods of time without affecting the health of the cornea, they need to be manufactured from the highest oxygen transmissible material available. The long-term effect of thinning on the epithelium's barrier properties needs to be monitored closely.

Global topographical thickness of the cornea and epithelium was measured using OCT in normal, RGP lens wearing and keratoconic eyes. Corneal and epithelial thickness was not symmetrical across meridians. The epithelium of RGP lens wearers was slightly thinner than normal, but not as thin as in keratoconics, suggesting that the epithelial change seen in keratoconus is mainly due to the condition.

Post-LASIK corneal and epithelial thickness profiles were not the same for myopic and hyperopic subjects, since the ablation patterns vary. Epithelial thickening in the mid-periphery had not recovered by six months in myopes or hyperopes, possibly indicating epithelial hyperplasia. Light backscatter profiles were used to monitor the recovery of the LASIK flap interface, showing the band of light backscatter around the flap interface to decrease as the cornea healed.
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.
BIOMECHANICAL ALTERATION OF CORNEAL MORPHOLOGY AFTER CORNEAL REFRACTIVE THERAPY
(University of Waterloo, 2006) Lu, Fenghe
Purpose: Although orthokeratology (non-surgical corneal reshaping, Corneal Refractive Therapy, CRT®) has been used for almost a half century, contemporary CRT's outcomes and mechanisms still require investigation. A series of studies was designed to examine different aspects of non-surgical corneal reshaping for myopic and hyperopic corrections, including the efficacy and stability of this procedure, the effect of the lens material characteristics (Dk/t), and the corneal or superficial structural change (e. g. corneal/epithelial thickness) in corneal reshaping.
Methods: In the CRT® for myopia (CRT1) study, 20 myopes wore CRT® lenses on one eye and control lenses on the contralateral eye (eye randomized) for one night while sleeping. Corneal topography and refractive error were measured the night prior to lens insertion, immediately after lens removal on the following morning and at 20 and 60 minutes and 3, 6 and 12 hours later. In the CRT® for hyperopia (CRTH) study, 20 ametropes wore CRT®H lenses on one eye for one night while sleeping, the contralateral eye (no lens wear) served as control (eye randomized). Corneal topography, aberrations and refractive error were measured the night prior to lens insertion, immediately after lens removal on the following morning and at 1 and 3, 6, 12 and 28 hours later. In the relatively long term (4 weeks) CRT® for myopia (CRT2) study, 23 myopes wore CRT® lenses overnight and removed their lenses on awakening. Visual Acuity (VA), subjective vision, refractive error, aberrations, and corneal topography were measured at baseline, immediately after lens removal on the first day and 14 hours later, and these measurements were repeated on days 4, 10, and 28. The treatment zone size was demarcated by the change in corneal curvature from negative to positive and vice versa, using tangential difference maps from the corneal topographer. In the study of effects of Dk/t on CRT® for myopia (CRTHDK), 20 myopic subjects were fit with Menicon Z (MZ) lenses (Dk/t=90. 6, Paragon CRT®) on one eye and an Equalens II (EII) CRT® lenses (Dk/t=47. 2) on the contralateral eye (eye randomized). Corneal topography, refractive error and aberrations were measured before lens insertion (baseline), and the following day after overnight lens wear, on lens removal and 1, 3, 6, 12 hours later. In the study of short term effects of CRT® for myopia and hyperopia (STOK), 20 ametropes wore CRT® and CRT®H lenses in a random order on one eye (randomly selected). The lenses were worn for 15, 30 and 60 minutes (randomly ordered, with each period taking place on a different day). Refractive error, aberrations, corneal topography, and corneal/epithelial thickness (using OCT) were measured before and after lens wear. The measurements were performed on the control eyes at 60 minutes only.
Results: In the CRT1 study, after one night of CRT® for myopia, the central cornea flattened and the mid-periphery steepened, and myopia reduced. In the CRTH study, after one night of CRT® for hyperopia, the central cornea steepened and the para-central region flattened, myopia was induced or hyperopia was reduced, all aberrations except for the astigmatism increased and signed spherical aberration (SA) shifted from positive to negative. In the CRT2 study, after 4 weeks of CRT® lens wear, in general, the treatment zones stabilized by day 10, vision improved, myopia diminished, total aberration and defocus decreased and higher order aberrations (HOAs) including coma and SA increased. The visual, optical and subjective parameters became stable by day 10. In the CRTHDK study, after one night of CRT® (MZ vs. EII) lens wear, the central corneal curvature and aberration were similar with a slight exception: The mid-peripheral corneal steepening was greater in the EII (lower Dk/t) lens-wearing eyes compared to the MZ (higher Dk/t) eyes. In the STOK study, after brief CRT® and CRT®H lens wear, significant changes occurred from the 15 minutes time point: The corneal shape and optical performance changed in a predictable way; the central cornea swelled less than the mid-periphery after CRT® lens wear, whereas the central cornea swelled more than the para-central region after CRT®H lens wear; the central epithelium was thinner than the mid-periphery after CRT® lens wear and was thicker than the para-central region after CRT®H lens wear.
Conclusion: After one night of lens wear, CRT® and CRTH® lenses were effective for myopia and hyperopia correction, respectively. In the 4 week CRT study, the treatment zone size changed during the first 10 days. Its size was associated with VA, refractive error, aberrations, and subjective vision. In the CRTHDK study, after one night of lens wear, changes in corneal shape were slightly different, with more mid-peripheral steepening in the lower Dk lens-wearing eyes compared to the higher Dk lens-wearing eyes. Changes in central corneal shape and optical performance were similar in both eyes. In the STOK study, CRT® lenses for myopia and hyperopia induced significant structural and optical changes in as little as 15 minutes. The cornea, particularly the epithelium, is remarkably moldable, with very rapid steepening and flattening possible in a small amount of time.
Retinal Blood Flow and Vascular Reactivity in Diabetic Retinopathy
(University of Waterloo, 2006-12-18T16:07:34Z) Gilmore, Edward
Introduction Retinal vascular reactivity is impaired in patients with diabetes and is thought to be involved in the onset and progression of diabetic retinopathy (DR). Previous studies that have utilized hyperoxia to assess retinal vascular reactivity have been limited due to confounding factors associated with the administration of oxygen and have used a variety of different instruments to measure retinal blood flow. The influence of blood glucose at the time of blood flow assessment has also not been systemically investigated. The specific aims of each Chapter are as follows: Chapter 3: To compare three systems used to administer hyperoxia to human subjects. Chapter 4: To quantify the magnitude and timeline of change of retinal hemodynamic parameters induced by an isocapnic hyperoxic stimulus. Chapters 5, 6 and 7: To quantify the magnitude of change of retinal hemodynamic parameters induced by hyperoxia, hyperglycemia and combined hyperoxia / hyperglycemia, respectively, in groups of diabetic patients with no clinically visible, and mild-to-moderate, DR and in age-matched subjects without diabetes. Methods Chapter 3: Subjects breathed air followed by oxygen, or oxygen plus carbon dioxide using a non-rebreathing system, or air followed by oxygen using a sequential rebreathing system. The magnitude of change and variability of CO2 concentrations was compared between systems. Chapter 4: Baseline retinal blood flow data was acquired while the subjects breathed air using a sequential rebreathing system. An isocapnic hyperoxic stimulus was initiated and maintained for 20 minutes. Air was then re-administered for 10 minutes. Retinal blood flow measurements were acquired every minute over the course of the study. The magnitude of change of each hemodynamic parameter was determined by fitting individual data with a sigmoidal function. For Chapter 5, 6 and 7 diabetic patients with no clinically visible, and mild-to-moderate, DR were stratified into groups based upon their retinopathy status. Age-matched non-diabetic subjects were recruited as controls. Baseline retinal blood flow data was acquired while subjects breathed air. Retinal blood flow measurements were then acquired after exposure to (a) hyperoxia, (b) hyperglycemia and (c) combined hyperoxic / hyperglycemic stimuli. Change in hemodynamic parameters was compared between groups and correlated with objective measures of retinal edema. Results Chapter 3: The difference in group mean end-tidal CO2 levels between baseline and hyperoxia was significant for oxygen administration using a non-rebreathing system. The sequential rebreathing technique resulted in a significantly lower variability of individual CO2 levels than either of the other techniques. Chapter 4: An ~11% decrease of diameter, ~36% decrease of velocity and ~48% decrease of blood flow was observed in response to isocapnic hyperoxia in young, healthy subjects. A response time of 2.30±0.53 minutes and 2.62±0.54 minutes was observed for diameter and velocity, respectively. Chapter 5: Retinal blood velocity, flow, and WSR significantly decreased in response to isocapnic hyperoxia in all groups. The magnitude of the reduction of blood flow was significantly reduced with increasing severity of retinopathy. There was a significant relationship between baseline objective edema index values and retinal vascular reactivity. Chapter 6: A significant change in blood glucose level was observed for all groups. No significant change in any hemodynamic parameter was found in patients with diabetes and in age-matched subjects without diabetes. Chapter 7: Retinal blood velocity and flow significantly decreased in all groups in response to combined hyperoxic / hyperglycemic provocation. The vascular reactivity response was not significantly different across the groups. Conclusions Chapter 3: Control of CO2 is necessary to attain standardized, reproducible hyperoxic stimuli for the assessment of retinal vascular reactivity. Chapter 4: Arteriolar retinal vascular reactivity to isocapnic hyperoxic provocation occurs within a maximum of 4 minutes. Although there was a trend for diameter to respond before velocity, the response characteristics were not significantly different between diameter and velocity. Different response characteristics of the retinal vasculature to transmural pressure mediated autoregulation as opposed to metabolic mediated vascular reactivity are suggested. Chapter 5: The vascular reactivity response in terms of the reduction of blood flow relative to baseline was significant in all groups but the magnitude of the change in flow was significantly reduced with increasing severity of retinopathy. A loss of retinal vascular reactivity is indicated in patients with moderate DR without clinically evident diabetic macular edema (DME), and in patients with DME. Chapter 6: Unaltered retinal arteriolar blood flow was found 1 hour after glucose ingestion in patients with diabetes and in age-matched subjects without diabetes. These results do not support the theory that retinal blood flow is affected by an acute increase of blood glucose in diabetic patients and in subjects without diabetes. Chapter 7: The vascular reactivity response to a combined hyperoxic / hyperglycemic provocation produced a pronounced reduction in blood flow. Unlike the response to hyperoxia alone, the vascular reactivity response was not significantly different across the groups. This suggests that hyperglycemia may influence the retinal vascular reactivity response to hyperoxia.
The Relationship between Retinal Vascular Reactivity and Arteriolar Diameter
(University of Waterloo, 2006-12-18T18:28:56Z) Tayyari, Faryan
ABSTRACT Purpose: The primary aim of the study (i.e. Chapter 3) was to compare the magnitude of retinal vascular reactivity in arterioles of varying diameter in healthy, young subjects. The secondary aims were to determine: a) if there are any order effects in terms of provoking vasoconstriction or vasodilation first; and b) the repeatability of the vascular reactivity measurements. An additional aim (i.e. Chapter 4) was to determine the effect of healthy aging on the relationship between retinal vascular reactivity and vessel diameter. Method: The sample comprised 10 healthy, young subjects (mean age 26.5 years, SD 4.04) and 7 healthy, older subjects (mean age 55.43 years, SD 5.41). Each subject from the young age group attended for three sessions. The first session was used to determine eligibility and select hemodynamic measurement sites. At sessions 2 and 3, O2 and CO2 were sequentially administered to the subjects using a face mask and sequential re-breathing circuit (to maintain standardized hyperoxia and hypercapnia). The order of vasoconstriction and vasodilation was varied across sessions 2 and 3. The design of the protocol was simplified for the subjects from the older age group. Each subject from the older group attended for one visit. O2 and CO2 were administered to the subjects using a face mask and sequential re-breathing circuit. The order of gas provocation was varied among the subjects (i.e. hyperoxia or hypercapnia first). For both groups, measurements of vessel diameter, centerline blood velocity and derived blood flow were acquired at each condition (i.e. baseline, during stabilized vasoconstriction, vasodilation, and recovery) at two discrete measurement sites along the supero-temporal arteriole. Results: The results of the repeated measures ANOVA showed a significant difference between the narrow and wide measurement sites for the younger group for flow (p≤ 0.0003) and a significant influence of inspired gas provocation on flow for both protocols (p<0.0001). In addition, the interaction of measurement site and inspired gas provocation was significant (p<0.0001). The magnitude of retinal vascular reactivity showed a significantly greater blood flow response for the wide measurement site (p<0.0001). O2 provocation resulted in vasoconstriction that was still present up to 10 minutes after cessation of the stimulus (order effect of O2; p≤0.046). No such order effect was apparent for CO2 provocation (order effect of CO2; p=0.352). The group mean blood flow Coefficient of Repeatability (COR) for the narrow measurement site was 0.74 µl/min (relative to group mean flow of 4.85 µl/min ± SD 1.31) and for the wide measurement site was 1.49 µl/min (relative to group mean flow of 11.29 µl/min ± SD 3.55). There was no difference between the young and the older age groups in retinal vascular reactivity for both the narrow (two-tailed Student t-test, p=0.8692) and wide (two-tailed Student t-test, p=0.2795) measurement sites. Conclusion: This study demonstrated that the magnitude of retinal vascular reactivity was greater for arteriolar measurement sites with wider baseline vessel diameters. In addition, it demonstrated that hyperoxic provocation resulted in a persistent vasoconstriction up to 10 minutes after cessation of the stimulus. The study demonstrated that the repeatability of retinal blood flow measurements in absolute terms is lower for smaller diameter vessels. Finally, this study also suggests that age does not affect the relationship between retinal vascular reactivity and vessel diameter.
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 Role of MMPs, Smad3 and Heat Shock Proteins in TGF-β-Induced Anterior Subcapsular Cataract Development
(University of Waterloo, 2007-06-18T18:38:20Z) Banh, Alice
Transforming growth factor beta (TGF-β) has been implicated in anterior subcapsular cataract (ASC) development. In the first section of this thesis, an in-vitro rat lens model was used to determine the role of matrix metalloproteinases during TGF-β-induced ASC. In the second part, an in-vivo TGF-β transgenic and Smad3 knockout model was used to examine the role of Smad3 signaling pathway in TGF-β-induced ASC development. Lastly, an in-vitro rat lens epithelial explant culture model was used to investigate the potential role of heat shock proteins (Hsps) in TGF-β-induced epithelial-mesenchymal transition (EMT). Optical, morphological and molecular changes were analyzed in theses studies. Results from cultured rat lenses show a significant increase of back vertex distance variability (decrease of sharpness and focus) during ASC development. Inhibition of MMPs eliminated the TGF-β-induced plaque formation. Similarly, the overexpression of TGF-β1 in transgenic mouse lenses leads to ASC formation and a decrease in lens optical quality in comparison to wild-type lenses, while TGF-β1/Smad3-/- (null) lenses show diminished TGF-β-induced effects. The plaques formed in the TGF-β1/Smad3-/- lenses are substantially smaller than in the TGF-β1/Smad3+/+ lenses. The morphological and molecular changes of TGF-β2/FGF-2 treated rat lens epithelial explants are similar to those found in the TGF-β2 treated rat lenses and transgenic TGF-β1 mouse lenses. Heat shock treatment prior to TGF-β treatment significantly reduced the effects of EMT in rat LECs. In conclusion, MMP inhibition prevented TGF-β-induced ASC formation whereas heat shock treatment and the absence of Smad3 protein expression only reduced the severity of TGF-β-induced effects.
Talking with and about older adult patients: The socializing power of patient-centered communication in an optometry teaching clinic
(University of Waterloo, 2007-07-31T13:28:08Z) Hildebrand, Jenna Mae
In a teaching clinic, healthcare students and their supervisors talk with their patients in the examination room and they talk about their patients during teaching consultations outside the examination room. Effective doctor-patient communication helps to establish management plans that are appropriate for both doctors and their patients. Amid a pressure to provide more patient-centered care, communicating effectively with older adult patients is particularly crucial because the occurrence of health problems and the likelihood of age-based communication barriers and negative attitudes increase with age. This project is a qualitative, collective case study of eye examinations, case presentations and participant interviews. This study took place in the Primary Care Clinic at the University of Waterloo, School of Optometry. Participants included 8 fourth-year optometry students, 5 supervising optometrists, and 10 patients between 60 and 85 years of age. The study involved audio-recording and analyzing eye examinations of older adult patients, case discussions about these patients, and interviews of older adult patients, optometry students and their optometrist supervisors. Data were analyzed using a constant-comparative approach, consistent with grounded theory. This study identified some of the discursive features of and reflections about patient-centered communication during the talk with and about older adult patients. During the eye examinations, optometry students incorporated five types of verbal communication that were consistent with a patient-centered model: Patient Agenda, Social Talk, Analogies, Patient Agency, and Health Promotion & Prevention. Although these successful attempts to incorporate patient-centered communication strategies were evident in the talk with patients, optometry students routinely engaged in seven other verbal strategies that challenged this patient-centered ethos: Closed-Ended Questions, Biomedical and Technical Language, Patient as a Problem, Unacknowledged Patient Voice, Patient Understanding, Doc Talk, and Caregiver Agency. Two types of discursive strategies related to patient-centered care were identified in the talk about older adult patients during novice case presentations: Voice of Optometry and Voice of Patient. The Voice of Optometry incorporated field-sanctioned language strategies including three subcategories: Biomedical, Technical and Judgment. In contrast, the Voice of Patient represented various levels of patient agency: Passive Recipient, Negotiated Agency and Patient Agency. According to their interviews, optometry students received limited explicit training, in both classroom and clinic instruction, on how to talk with and about patients. During their interviews, optometry students and their supervisors made clear distinctions between patient–centered and doctor-centered care. Most of the students and supervisors believed that the optometry profession and the optometry school promoted patient-centered care. Elements of patient voice were represented in the eye examinations, the case presentations and the post-examination patient interviews. During novice case presentations patient voice was often fragmented into sound bytes of the original patient statements or translated into field-sanctioned language. Although many instances of patient education and counselling were evident throughout the eye exams, limited discussion occurred in the novice case presentations between students and their instructors about what to say to patients, In addition, the majority of topics addressed during educational and counselling moments were not discussed during the novice case presentations. Additionally, post-examination patient recall regarding education and counselling was generally limited. Throughout this study, talk about age appeared in four ways: 1) caregivers used age to make clinical decisions during case presentations, 2) caregivers referenced age during counseling and education to explain eye and vision changes, 3) patients commented on the impact of age on themselves, and 4) caregivers spoke about how they considered age when speaking to their patients. While the caregivers generally valued a patient-centered approach, the talk with and about patients was skewed towards strategies that may limit the ability to support this ethos. It is questionable what audience (i.e. patient or supervisor) optometry students value and how this affects their ability to adopt patient-centered communication strategies. Findings from this study suggest that caregivers and their patients might benefit from some changes in the way patient-centered practice is taught and practiced in this optometry teaching clinic. As a greater understanding develops of the strategies of and challenges to patient-centered practices in optometry, it is my hope that optometry training programs as well as optometry professional organizations will further embrace patient-centered practices.
Longitudinal impact of newly acquired closed-circuit televisions (CCTV) on quality of life for low vision patients
(University of Waterloo, 2007-08-09T19:05:52Z) Huber, Jessica
Ongoing efforts to quantify changes in quality of life attributable to low vision rehabilitation have focused on the utility of a single test instrument to measure this multidimensional concept. It is hypothesized that quality of life is best assessed using multiple instruments to capture some of its component facets, including functional status and psychosocial impact. Low vision devices have a predictably spontaneous impact on functional vision status, but associated psychosocial impact occurs with different magnitudes and over more protracted time intervals. The National Eye Institute Visual Function Questionnaire (NEI VFQ-25) measures the functional status of individuals in key vision areas that are associated with quality of life. The Psychosocial Impact of Assistive Devices Scale (PIADS) is an instrument that measures the psychosocial impact of assistive device intervention in three quality of life domains: competence, adaptability, and self-esteem. 68 participants were obtained from an ongoing parent study. These participants were recruited through the Low Vision Clinic at the University of Waterloo. They had a primary diagnosis of age-related macular degeneration (ARMD) and were obtaining a CCTV system for the first time. Assessments from the parent study used in this thesis included follow-up from 2 weeks, 1 month, 3 months, and 6 months post-adoption of the CCTV. The two tests administered were to measure functional vision status (NEI VFQ-25) and perceived psychosocial impact (PIADS), according the framework outlined by the Consortium for Assistive Technology Outcomes Research (CATOR). Multivariate repeated-measures ANVOA results confirmed that CCTV systems have an immediate and robust effect on the daily visual functioning of their users, and that this effect is stable over long periods of device use. The psychosocial impact of CCTV device use peaks in the shorter term and then seems to wane in the longer term for reasons that are not yet understood. The NEI VFQ-25 and the PIADS appear to have differential sensitivity to important influences on low vision rehabilitation outcomes. This project has demonstrated the value of longitudinal outcomes research in low vision rehabilitation. After obtaining a CCTV, visual function status remains static while psychosocial impact is dynamic during 6-months of follow-up.
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.
Effect of vergence adaptation and positive fusional vergence training on oculomotor parameters
(University of Waterloo, 2008-01-24T21:06:15Z) Thiagarajan, Preethi
Accommodation and vergence, the two important oculomotor systems, exhibit the property of adapation which maintains the response for comfortable prolonged viewing. Several mathematical models have been developed to describe the basic underlying mechanism of accommodation and vergence. Currently used models contradict with each other in the placement of critical elements in the model. This thesis addressed this controversy and empirically verified these models. The effect of vergence adaptation and its influence on certain critical oculomotor parameters have been evaluated in two studies. The specific aims, methods, results and conclusions of each chapter are as follows: Chapter 3 Aim To evaluate the effect of vergence adaptation on convergence accommodation (CA) response and the effect of CA stimulation on accommodative adaptation to determine the model that best fits human accommodation and vergence interaction. Methods This study investigated the effect of vergence adaptation on the convergence accommodation (CA) response as a function of vergence stimulus magnitude and duration in 10 emmetropes. Convergence was induced using no prism, 6, and 12 prism dioptres as stimuli at 0.4m, viewed for 5, 10 & 15 minutes of duration in randomized separate sessions. Phoria measures and CA responses were recorded at the baseline, immediately following prism insertion and following specific durations of viewing through the prism (post-task). Also the effect of CA cross-link on the tonic accommodation (TA) adaptation was investigated where TA response was measured before and after the convergence task. Results & conclusions Repeated measures of ANOVA showed no significant (p > 0.05) phoria adaptation or CA response change with no prism as the stimulus. For 6 and 12 prism dioptres, there were significant reductions (p< 0.01) in CA with phoria adaptation. No significant (p>0.05) phoria adaptation or reduction in the CA response between 5, 10 and 15 minutes of viewing showing no effect of duration. No significant difference (p = 0.85) between the pre and post task TA response while vergence was adapted. The results of the study show that vergence adaptation reduces CA response supporting models which predict the CA crosslink to reduce its output as tonic vergence adaptation progresses. However the convergence accommodation does not appear to lead to increased output of tonic accommodation. Chapter 4 Aim The purpose of this study was to evaluate certain critical parameters of vergence and accommodation under vergence adaptation (induced with a BO Δ), before and after positive fusional vergence training. Methods Eleven emmetropes with normal binocular vision participated in the study. Distance & near phoria, AC/A & CA/C ratios, & positive fusional amplitude at near were evaluated before and after two weeks of positive fusional vergence training. Phoria adaptation and CA responses were monitored every 3 minutes for 15 minutes while the subjects viewed through 12Δ BO under open-looped accommodation at 0.4m before and after training. On a separate vergence adaptation session (before training), phoria adaptation was induced under dual closed-loop condition using 12Δ BO at 0.4m. Cross-link ratios, BO fusional amplitude at 0.4m and near phoria were measured following 15 minutes of prism adaptation. Subjects underwent 2 weeks of positive fusional vergence training using variable tranaglyphs and aperture rule at 0.4m. Phoria adaptation and CA responses monitored over time were exponentially fit and were compared before and after training. AC/A & CA/ C ratios and BO to blur value at 0.4m taken before training, under the vergence adapted state and after training were analyzed using repeated measures ANOVA. Results & conclusions No significant difference (p > 0.05) in the cross-link ratios were found before and after training. However, there was a significant (p < 0.01) increase and decrease in the AC/A and CA/C ratios respectively under the vergence adapted state. BO to blur value at 0.4m was significantly increased (p < 0.01) from the pre training value under both vergence adapted condition and following training. Rate constants and magnitudes of phoria adaptation and CA response reduction were significantly (p < 0.01) different following training demonstrating robust and greater magnitude of vergence adaptation in the BO direction reducing the CA response faster. However, this improved vergence adaptability is not reflected in the static measures of AC/A and CA/C ratios. The increased BO to blur value following training is caused by the increased speed of prism adaptation reducing the CA response during BO fusional amplitude testing.
Binocular adaptation to near addition lenses in emmetropic adults
(Elsevier, 2008-05) Sreenivasan, Vidhyapriya; Irving, Elizabeth; Bobier, William
Near addition lenses are prescribed to pre-presbyopic individuals for treatment of binocular motor problems such as convergence excess and to control the progression of myopia. To date, no investigation has looked at the complete sequence of binocular motor responses during a period of near work with +2 D lenses. This investigation evaluated changes to accommodation and vergence responses when young adults sustained fixation at 33 cm with +2 D addition lenses. In addition, the effect of the accommodative vergence cross-link (AV/A) on the magnitude and the completeness of binocular adaptation to these lenses were evaluated. The results showed that +2 D lenses initiate an increase in exophoria and convergence driven accommodation. The degree of the initial induced phoria was dependant upon the magnitude of the AV/A ratio. Vergence adaptation occurred after 3 min of near fixation and reduced the exophoria and convergence driven accommodation. The magnitude of vergence adaptation was dependant upon the size of the induced phoria and hence the AV/A ratio. The completeness of adaptation was seen to vary inversely with induced exophoria and thus the AV/A ratio.

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