<em>Introduction:</em> 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. <br /><br /> <em>Methods:</em> 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. <br /><br /> 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. <br /><br /> 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. <br /><br /> <em>Results:</em> <br /> <em>Study 1:</em> 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. <br /><br /> <em>Study 2:</em> 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/&Delta; and 0. 15±0. 09 D/&Delta; 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). <br /><br /> <em>Conclusions:</em> 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.

<em>Introduction:</em> 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. <br /><br /> <em>Methods:</em> 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. <br /><br /> 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. <br /><br /> 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. <br /><br /> <em>Results:</em> <br /> <em>Study 1:</em> 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. <br /><br /> <em>Study 2:</em> 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/&Delta; and 0. 15±0. 09 D/&Delta; 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). <br /><br /> <em>Conclusions:</em> 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.

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. <br /><br /> 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). <br /><br /> 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. <br /><br /> 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.

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. <br /><br /> 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). <br /><br /> 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. <br /><br /> 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.

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.

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.

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 ??g/lens versus 1. 9??0. 8 ??g/lens, p<0. 001), lysozyme deposition (0. 7??0. 5 ??g/lens versus 1. 1??0. 7 ??g/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 ??g/lens), reached a maximum on the 7th day (1386??21 ??g/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.

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 <em>in vitro</em> doping and <em>in vivo</em> 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 <em>in vitro</em> 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 <em>in vitro</em> deposition studies influenced the ultimate amount and composition of lipid deposits. <em>In vivo</em> 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.

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. <br /><br /> 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. <br /><br /> 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. <br /><br /> 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. <br /><br /> 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. <br /><br /> 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. <br /><br /> 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. <br /><br /> 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. <br /><br /> 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. <br /><br /> 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.

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.