Changes in corneal thickness, corneal volume, and densitometry after long-term orthokeratology wear.

PURPOSE: To investigate changes in the corneal volume, corneal densitometry and pachymetry of young myopes wearing over-night orthokeratology (OK) contact lenses. METHODS: The medical records of 28 right eyes of young myopes wearing OK between 2013 and 2018 were reviewed retrospectively. The baseline refractive error, best corrected visual acuities at baseline and uncorrected visual acuity at the most recent visit were recorded. Corneal volume of the central 10 mm cornea; densitometry at central, nasal and temporal cornea; and pachymetry along the horizontal and vertical meridians were collected from the Pentacam® HR at baseline, after one night of lens wear, and at the latest visit. RESULTS: The mean age of subjects was 12.03 ± 3.80 years at the time of OK lens fitting and wore OK overnight for a mean duration of 666 days (range 206-1736 days). The baseline spherical equivalent refractive error was -3.03 ± 1.56 D (range -1.00 to -6.00 D). The corneal volume increased significantly after OK wear (p = 0.001). Corneal densitometry increased after OK wear, but the change did not reach statistical significance (p = 0.113). Pachymetry in the central cornea did not change significantly across all visits (p > 0.05) but increased significantly in the mid-peripheral regions of the cornea. Baseline refractive error was not found to be correlated with the changes in corneal volume, corneal densitometry, or pachymetry. CONCLUSION: The increase in corneal volume and densitometry and no significant change in the central corneal thickness may indicate the presence of corneal oedema from long-term OK wear. The baseline refraction was not correlated with the changes in corneal volume, densitometry or pachymetry.

Impact of contact lens wear on epithelial alterations in keratoconus

PURPOSE: The purpose of this study was to characterize the central epithelial thickness (CET) of penetrating keratoplasty corneal specimens obtained from patients with keratoconus (KC) and correlate the histological patterns with their clinical history. METHODS: Ex vivo histological imaging was performed to measure CET and total corneal thickness (TCT) in 56 patients with KC. Microscopic slides from penetrating keratoplasty corneal specimens, stained with hematoxylin and eosin were evaluated using bright field microscopy. CET and TCT were measured, and morphological features were studied. Clinical history regarding duration of KC prior to surgery and length of and tolerance to contact lens wear were compared and analyzed. RESULTS: The microscopic slides of all patients available for follow up (n = 48) were analyzed and CET and TCT were measured. The histological evaluation revealed 3 distinctive epithelial patterns. Pattern 1 with central hypertrophic and hydropic changes (n = 19) measured 70.89 ± 25.88 Mum in CET and 308.63 ± 100.74 Mum in TCT; Pattern 2 (n = 14) had not changed, similar to normal epithelium CET and TCT measuring 36.5 ± 7.02 Mum and 260.14 ± 87.93 Mum respectively. Pattern 3 (n = 15) demonstrated thinner central epithelium characterized by atrophy and focal hydropic changes measuring 19.93 ± 4.60 Mum and 268.00 ± 79.39 Mum in CET and TCT respectively (all p < 0.0001). The presence of Pattern 2 characterized by similar to normal CET was correlated with the duration of the condition (R = 0.600, p = 0.030). There was a significant difference in the length of CL wear comparing those with patterns 1 and 2 versus 3 (least no. of CL years) (p = 0.05 and p = 0.33 respectivelly). CONCLUSIONS: Patients with advanced disease have various central corneal epithelial changes detected with histology. Although each central epithelial pattern type was distinctive comparing the 3 patterns, there was no correlation with years of CL wear but only with the duration of the condition

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Comparative Analysis of Tear Proteins in Keratoconic Scleral Lens Wearers with Variation in Limbal Clearance.

SIGNIFICANCE: Cytokine and protease analysis revealed relative changes in the post-lens tear film of scleral lenses with low and high limbal clearances. Results from this study indicate that midperipheral lens fit is an important fitting feature that can impact the inflammatory response of a keratoconic eye. PURPOSE: The purpose of this study was to investigate changes in levels of inflammatory mediators in the post-lens tear film of keratoconic scleral lens wearers with varying limbal clearance designs. METHODS: Twenty-two keratoconic eyes were fitted with two sets of scleral lenses that were consistent in lens diameter and central sagittal depth but varied in limbal clearance by approximately 50 µm. Lenses were worn in a randomly assigned order for a 2-week period each. At each follow-up visit, immediately after lens removal, tear samples were collected with a microcapillary tube (10 µL, 0.5 mm in diameter) from the bowl of the inverted scleral lens. Tear cytokine and protease analysis was performed using a multiplex electrochemiluminescent array (Meso Scale Discovery, Rockville, MD) instrument. Levels of interleukins 1, 6, and 8; tumor necrosis factor α; and matrix metalloproteinases 1 and 9 were compared and analyzed. RESULTS: Levels of interleukin 1ß, tumor necrosis factor α, and matrix metalloproteinase 1 increased with high limbal clearance (P = .01, .006, and .02, respectively). No change in interleukins 6 and 8 levels was found (P > .05). A decrease in matrix metalloproteinase 9 was noted in post-lens tear film of scleral lenses with high limbal clearance (P = .10). DISCUSSION: Relative changes in the cytokine and protease levels were found when comparing low and high limbal clearance, indicating that the midperipheral lens fit is an important feature that can impact the inflammatory response of the keratoconic eye.

Impact of contact lens wear on epithelial alterations in keratoconus.

PURPOSE: The purpose of this study was to characterize the central epithelial thickness (CET) of penetrating keratoplasty corneal specimens obtained from patients with keratoconus (KC) and correlate the histological patterns with their clinical history. METHODS: Ex vivo histological imaging was performed to measure CET and total corneal thickness (TCT) in 56 patients with KC. Microscopic slides from penetrating keratoplasty corneal specimens, stained with hematoxylin and eosin were evaluated using bright field microscopy. CET and TCT were measured, and morphological features were studied. Clinical history regarding duration of KC prior to surgery and length of and tolerance to contact lens wear were compared and analyzed. RESULTS: The microscopic slides of all patients available for follow up (n=48) were analyzed and CET and TCT were measured. The histological evaluation revealed 3 distinctive epithelial patterns. Pattern 1 with central hypertrophic and hydropic changes (n=19) measured 70.89±25.88µm in CET and 308.63±100.74µm in TCT; Pattern 2 (n=14) had not changed, similar to normal epithelium CET and TCT measuring 36.5±7.02µm and 260.14±87.93µm respectively. Pattern 3 (n=15) demonstrated thinner central epithelium characterized by atrophy and focal hydropic changes measuring 19.93±4.60µm and 268.00±79.39µm in CET and TCT respectively (all p<0.0001). The presence of Pattern 2 characterized by similar to normal CET was correlated with the duration of the condition (R=0.600, p=0.030). There was a significant difference in the length of CL wear comparing those with patterns 1 and 2 versus 3 (least no. of CL years) (p=0.05 and p=0.33 respectivelly). CONCLUSIONS: Patients with advanced disease have various central corneal epithelial changes detected with histology. Although each central epithelial pattern type was distinctive comparing the 3 patterns, there was no correlation with years of CL wear but only with the duration of the condition.

The contact Lens risk survey to assess risk of soft contact lens-related inflammatory events.

PURPOSE: To test the Contact Lens Assessment in Youth Contact Lens Risk Survey (CLRS) scoring algorithm in soft contact lens (SCL) wearers presenting with SCL-related adverse events and healthy matched controls. METHODS: This prospective case-control study compared CLRS responses in SCL wearers presenting with symptomatic red eyes (Cases) with age-, sex- and site-matched healthy SCL wearers (Controls) at six locations across North America. Responses to individual questions from Cases and Controls were analyzed using either the Pearson, Mantel-Haenszel chi-square, or Fisher's exact test. Differences in the CLRS scores were compared using t-tests. RESULTS: A total of 171 SCL wearers were enrolled (n = 57 Cases, 114 Controls). Cases were adjudicated to consensus and classified as contact lens-related serious and significant (S&S) or non-serious events. S&S Cases scored significantly higher on the CLRS (56.1 ±â€¯11.1) than either their matched Controls (44.3 ±â€¯11.1) (P <  0.001) or the non-Serious Cases (44.8± 12.8 P =  0.002). Scores of non-serious Cases were not significantly different than scores of their Controls (43.4 ± 10.7, P = 0.33) CONCLUSIONS: The CLRS scoring algorithm discriminated between SCL wearers presenting with S&S CL-related adverse events from healthy SCL wearers and those with non-serious events. This survey and scoring system could help practitioners identify patients at greatest risk for CL-related adverse events and support targeted interventions aimed at reducing risk behaviors.

Development of a contact Lens risk survey.

PURPOSE: To describe the development and report psychometric properties of the Contact Lens Risk Survey (CLRS) to identify patients at risk for soft contact lens-related complications. METHODS: Psychometric properties of the CLRS, a web-based survey with branching logic, were determined using data from 5 multi-site fieldings (n = 1059), including re-fielding to sub groups. Responses from participants with and without an active red eye were used to identify risk factors of a red eye event and calculate an overall risk score. A 6th fielding of the CLRS (n = 171) was used to assess discriminate validity. RESULTS: Participants needed 11-12 min to complete the survey with a negligible difference by age. Internal consistency was excellent (Cronbach's α ≥ 0.70) for 3 of the 5 constructs identified by factor analysis. Twelve of the 17 survey items exhibited excellent within-subject repeatability (Kappa ≥ 0.61). Between-subject agreement, assessed in 18-25 year olds, was high for the majority of items, suggesting good generalizability across different populations of SCL wearers. The ability of the model using individual items of the CLRS to discriminate Controls and participants with a red eye was good with an area under the curve of 0.779. CONCLUSION: The CLRS tool is a repeatable and valid instrument to standardize documentation of demographic, behavior, and exposure factors which appear to drive the greatest risk of a contact lens related red eye event.

Factors affecting central corneal thickness measurement agreement between Scheimpflug imaging and ultrasound pachymetry in keratoconus.

PURPOSE: To evaluate the agreement of central corneal thickness (CCT) measurement between Scheimpflug imaging and ultrasound (U/S) pachymetry in keratoconic eyes, and investigate factors that affect the agreement. METHODS: This post hoc analysis within a prospective, observational non-randomised study preformed at the Kensington Eye Institute, Toronto, Ontario, Canada, included crosslinking candidates with progressive keratoconus (KC). Main outcome measures were the agreement of CCT measurement between Scheimpflug imaging (Pentacam Oculus, Wetzlar, Germany) and U/S pachymetry (PachPen 24-5100, Accutome Inc., Malvern, Pennsylvania, USA), and factors that affect the agreement. RESULTS: A total of 794 keratoconic eyes of 456 subjects with a mean age of 27.6±8.0 years (69.7% males and 49.6% right eyes) were included. Agreement between devices was moderate (intraclass correlation coefficient: 74.9%, Bland-Altman limits of agreement: -48.5 µm to +62.5 µm). In a multivariable analysis, cone decentration (p<0.001, coefficient +10.13 [+6.73 to +13.53 95% CIs]) and Kmax (p<0.001, coefficient +0.68 [+0.46 to +0.90 95% CIs]) were significantly associated (both clinically and statistically) with the level of agreement between the devices; the discrepancy in CCT between the devices increased on average by 10.13 µm for every mm of cone decentration, and by 6.8 µm for every 10D of Kmax. Age, corneal astigmatism and spherical equivalent were statistically but not clinically significant factors affecting agreement. CONCLUSION: The agreement of CCT measurement between Scheimpflug imaging and U/S pachymetry in KC was moderate. To ensure the safety of crosslinking in keratoconic corneas, Scheimpflug and U/S CCT measurements should not be used interchangeably, especially in steep corneas and corneas with decentred cones.

Objective and Subjective Evaluation of Clinical Performance of Scleral Lens with Varying Limbal Clearance in Keratoconus.

SIGNIFICANCE: This study evaluates how limbal clearance (LC) may impact the clinical performance of scleral lenses based on subjective response on comfort and ocular responses. Limbal zone designs in scleral lenses might affect the integrity of the limbal epithelial tissue as a result of a combined hypoxic and compression-related etiology. PURPOSE: This study aimed to investigate the clinical performance and ocular and subjective responses to the wear of scleral lenses having varying LC. METHODS: Lenses with varying LC with a difference of 50 µm were fitted on and compared among keratoconic participants. The lenses were worn during a 2-week period. Visual analog scales concerning subjective comfort were completed. Ocular surface findings including hyperemia, limbal staining, and corneal swelling were compared. RESULTS: Participants reported greater comfort achieved with high LC. No difference in limbal and bulbar hyperemia was found (P > .05). Corneal response to scleral lens wear with both low and high LCs seems to result in similar perilimbal staining and negative corneal staining. An increase in corneal pachymetric values was noted at the central and peripheral cornea, with no difference between low- and high-LC lenses (all, P < .05). Quadrant-specific analysis indicated that all meridians at both 6 and 8 mm were increased for the low-LC lenses (all, P < .05) and only the temporal region for the high-LC lenses (P = .02). CONCLUSIONS: Limbal clearance may play an important role in subjective performance in scleral lenses but does not impact the degree of hyperemia in either the limbal or bulbar region. Although low LC might result in more compression-related changes to ocular surface, high LC is associated with greater comfort and greater edematous changes. Limbal zone designs in scleral lenses might affect the integrity of the limbal epithelial tissue as a result of a combined hypoxic and compression-related etiology.

The Impact of Scleral Contact Lens Vault on Visual Acuity and Comfort.

PURPOSE: To assess how varying degrees of corneal clearance of scleral contact lenses (ScCL) impact visual acuity (VA) and comfort in patients with corneal ectasia. METHOD: Three ScCL were fitted to 20 subjects with previous diagnosis of either keratoconus (n=18) or pellucid marginal degeneration (n=2). Fitting of ScCL was based on corneal sagittal height (CSH) measured with Visante OCT at a 15-mm chord on the horizontal meridian. To select the ScCL from the diagnostic lens set, values of 325, 375, and 425 µm were randomly added in sequence to CSH. Subjects wore ScCL for 1 hr. Central corneal clearance (CCC) and topographic corneal clearance (TCC) along the vertical meridian were assessed using an ultralong optical coherence tomographer. High-contrast VA (HCVA) and low-contrast VA (LCVA) were measured using a logarithm of the minimum angle of resolution VA chart, and comfort ratings were obtained with a standard comfort scale (0-100). RESULTS: Mean CSH in the horizontal meridian was 3.78±0.53 (range: 3.33-4.17) mm at a 15-mm chord. Mean CCC was 190±100 µm (TCC: 160±94 µm at +3 mm and 180±94 µm at -3 mm), 360±120 µm (TCC: 260±100 µm at +3 mm and 330±110 µm at -3 mm), and 450±170 µm (TCC: 320±120 µm at +3 mm and 400±120 µm at -3 mm) for each lens (P=0.001). Mean HCVA for lenses 1, 2, and 3 were 0.05±0.12, 0.07±0.11, and 0.11±0.08 respectively, which were significantly different (P=0.02). Tukey post hoc analysis showed that this difference was only significant between lenses 1 and 3 (P=0.01). Similar findings were found for LCVA. Comfort ratings for lenses 1, 2, and 3 were 74.9±9.2, 79.7±11.6, and 78.6±10.8, respectively (P=0.24). CONCLUSION: The CSH is an effective method of determining the appropriate lens/cornea relationship. Lens 2 (+375 µm) gave the best combination of acuity and comfort ratings. Evaluation of the fluorescein pattern must be balanced with VA and comfort ratings for successful fitting in a clinical setting.

Multicenter Testing of a Risk Assessment Survey for Soft Contact Lens Wearers With Adverse Events: A Contact Lens Assessment in Youth Study.

PURPOSE: To test the ability of responses to the Contact Lens Assessment in Youth (CLAY) Contact Lens Risk Survey (CLRS) to differentiate behaviors among participants with serious and significant (S&S) contact lens-related corneal inflammatory events, those with other events (non-S&S), and healthy controls matched for age, gender, and soft contact lens (SCL) wear frequency. METHODS: The CLRS was self-administered electronically to SCL wearers presenting for acute clinical care at 11 clinical sites. Each participant completed the CLRS before their examination. The clinician, masked to CLRS responses, submitted a diagnosis for each participant that was used to classify the event as S&S or non-S&S. Multivariate logistic regression analyses were used to compare responses. RESULTS: Comparison of responses from 96 participants with S&S, 68 with non-S&S, and 207 controls showed that patients with S&S were more likely (always or fairly often) to report overnight wear versus patients with non-S&S (adjusted odds ratio [aOR], 5.2; 95% confidence interval [CI], 1.4-18.7) and versus controls (aOR, 5.8; CI, 2.2-15.2). Patients with S&S were more likely to purchase SCLs on the internet versus non-S&S (aOR, 4.9; CI, 1.6-15.1) and versus controls (aOR, 2.8; CI, 1.4-5.9). The use of two-week replacement lenses compared with daily disposables was significantly higher among patients with S&S than those with non-S&S (aOR, 4.3; CI, 1.5-12.0). Patients with S&S were less likely to regularly discard leftover solution compared with controls (aOR, 2.5; CI, 1.1-5.6). CONCLUSIONS: The CLRS is a clinical survey tool that can be used to identify risky behaviors and exposures directly associated with an increased risk of S&S events.

250 kHz, 1.5 µm resolution SD-OCT for in-vivo cellular imaging of the human cornea.

We present the first spectral domain optical coherence tomography (SD-OCT) system that combines an isotropic imaging resolution of ~1.5 µm in biological tissue with a 250 kHz image acquisition rate, for in vivo non-contact, volumetric imaging of the cellular structure of the human cornea. OCT images of the healthy human cornea acquired with this system reveal the cellular structure of the corneal epithelium, cellular debris and mucin clusters in the tear film, the shape, size and spatial distribution of the sub-basal corneal nerves and keratocytes in the corneal stroma, as well as reflections from endothelial nuclei. The corneal images presented here demonstrate the potential clinical value of the new high speed, high resolution OCT system for non-invasive diagnostics and monitoring the treatment of corneal diseases.

Scleral Lens Clearance Assessment with Biomicroscopy and Anterior Segment Optical Coherence Tomography.

SIGNIFICANCE: It is important to be able to accurately estimate the central corneal clearance when fitting scleral contact lenses. Tools available have intrinsic biases due to the angle of viewing, and therefore an idea of the amount of error in estimation will benefit the fitter. PURPOSE: To compare the accuracy of observers' ability to estimate scleral contact lens central corneal clearance (CCC) with biomicroscopy to measurements using slit-lamp imaging and anterior segment optical coherence tomography (AS-OCT). METHODS: In a Web-based survey with images of four scleral lens fits obtained with a slit-lamp video imaging system, participants were asked to estimate the CCC. Responses were compared with known values of CCC of these images determined with an image-processing program (digital CCC) and using the AS-OCT (AS-OCT CCC). Bland-Altman plots and concordance correlation coefficients were used to assess the agreement of CCC measured by the various methods. RESULTS: Sixty-six participants were categorized for analysis based on the amount of experience with scleral lens fitting into novice, intermediate, or advanced fitters. Comparing the estimated CCC to the digital CCC, all three groups overestimated by an average of +27.3 ± 67.3 µm. The estimated CCC was highly correlated to the digital CCC (0.79, 0.92, and 0.94 for each group, respectively). Compared with the CCC measurements using AS-OCT, the three groups of participants overestimated by +103.3 µm and had high correlations (0.79, 0.93, and 0.94 for each group). DISCUSSION: Results from this study validate the ability of contact lens practitioners to observe and estimate the CCC in scleral lens fittings through the use of biomicroscopic viewing. Increasing experience with scleral lens fitting does not improve the correlation with measured CCC from digital or the AS-OCT. However, the intermediate and advanced groups display significantly less inter-observer variability compared with the novice group.

Corneal, Conjunctival effects and blood flow changes related to silicone hydrogel lens wear and their correlations with end of day comfort.

PURPOSE: First, to examine how wearing high and low modulus lenses with two different base curves affected lens fit, and the corneal tissue and bulbar conjunctival vascular tissue (bulbar redness and blood velocity). Secondly, to quantify the associations between these baseline and outcome variables and the third purpose was to correlate these variables with end of day comfort. METHODS: Thirty participants wore higher (PureVision (PV) 8.3, 8.6) and lower (Acuvue Advance (AA) 8.3, 8.7) modulus silicone hydrogel lenses for two weeks on a daily wear basis. Lens fitting characteristics were examined. Corneal epithelial thickness was measured and the cornea and conjunctiva were assessed. RBC velocity was estimated from high magnification bulbar conjunctival images. Subjective comfort/dryness was reported by participants using visual analogue scales. RESULTS: AA lenses were rated the most comfortable (ANOVA, p=0.041). The least movement was while using the AA 8.3 base curve lens (Tukey p=0.028). Steep AA and PV lenses showed significantly higher conjunctival staining at the 2 week visit (ANOVA, p=0.029). There was a significant decrease in RBC velocity with both steeper AA lenses vs PV lenses (Tukey, p=0.001). Comparing baseline and 2 week visits, there was a significant negative correlation for the PV 8.3 between comfort and superior bulbar staining (r=-0.53). For both the PV 8.3 and AA 8.3 reduced RBC velocity was correlated with dryness (r=0.61 and r=0.91, respectively). CONCLUSIONS: Physical differences in contact lenses affect structural and vascular functional aspects of the ocular surface and these may be associated with symptoms of dryness.

In-vivo imaging of the palisades of Vogt and the limbal crypts with sub-micrometer axial resolution optical coherence tomography.

A research-grade OCT system was used to image in-vivo and without contact with the tissue, the cellular structure and microvasculature of the healthy human corneo-scleral limbus. The OCT system provided 0.95 µm axial and 4 µm (2 µm) lateral resolution in biological tissue depending on the magnification of the imaging objective. Cross-sectional OCT images acquired tangentially from the inferior limbus showed reflective, loop-like features that correspond to the fibrous folds of the palisades of Vogt (POV). The high OCT resolution allowed for visualization of individual cells inside the limbal crypts, capillaries extending from the inside of the POV's fibrous folds and connecting to a lateral grid of micro-vessels located in the connective tissue directly below the POV, as well as reflections from individual red blood cells inside the capillaries. Difference in the reflective properties of the POV was observed among subjects of various pigmentation levels of the POV. Morphological features observed in the high resolution OCT images correlated well with histology. The ability to visualize the limbal morphology and microvasculature in-vivo at cellular level can aid the diagnostics and treatment of limbal stem cell dysfunction and dystrophies.

Effect of Time on Scleral Lens Settling and Change in Corneal Clearance.

SIGNIFICANCE: With the increase in the use of scleral contact lenses among practitioners, questions regarding lens settling are gradually gaining attention. This is because current studies support the notion that scleral lenses settle back over time. More research is needed to understand the exact cause and the factors that underpin such phenomenon. PURPOSE: The present study aims to assess the effect of time on topographic corneal clearance of three scleral contact lenses of varying sagittal depths. METHODS: Three scleral contact lenses were fitted to 20 subjects with previous diagnosis of keratoconus (n = 18) or pellucid marginal degeneration (n = 2). The fit was based on corneal sagittal height measured with the Visante optical coherence tomographer (OCT) at 15 mm along the horizontal meridian. To select an appropriate lens from the diagnostic lens set, values of 325 µm (lens 1), 375 µm (lens 2), and 425 µm (lens 3) were randomly added in sequence to the corneal sagittal height. Subjects wore each lens for 1 hour. Corneal clearance was measured at 10-minute intervals for 1 hour using a custom ultra-long OCT. To assess change in clearance, central point and two mid-peripheral points (+3 mm and -3 mm) along an 8-mm chord were measured by taking differences at each time point up to 1 hour. Measurements were repeated for the two other lenses. RESULTS: Mean central corneal clearance loss for all three lenses was 33.83 ± 48.40 µm. This was 26 ± 27 µm (13 ± 14 µm, +3 mm; 34 ± 37 µm, -3 mm), lens 1; 35 ± 59 µm (38 ± 61 µm, +3 mm; 52 ± 69 µm, -3 mm), lens 2; and 41 ± 54 µm (33 ± 26 µm, +3 mm; 52 ± 48 µm, -3 mm), lens 3, respectively. There was no significant difference (P = 0.06) at central and other locations for lens 1 (location and over time). There were significant differences for both lenses 2 and 3 (P < .001, P = .01, respectively) for all three locations and over time. CONCLUSIONS: There is a likelihood of clearance loss after 1 hour of lens wear. This varies between subjects, initial lens-fit relationship, and over time.

Repeatability of topographic corneal thickness in keratoconus comparing Visante™ OCT and Oculus Pentacam HR® topographer.

PURPOSE: To assess the repeatability and reproducibility of Visante™ OCT and Oculus Pentacam HR® in measuring central (CCT) and topographic corneal thickness (TCT) along the principle meridians in keratoconus (KC) corneae. METHOD: Twenty participants diagnosed with KC were recruited. There were two study visits. On the first study visit, two repeated corneal thickness measurements were obtained with each instrument. Measurements were repeated at least 48hrs later in the same order. TCT were recorded in the 90, 180, 45 and 135 meridians at 1mm intervals across 8mm chord. RESULTS: Mean CCT for Visante™ OCT was 484.97±43.14µm (range: 484.84-486.09) and Oculus Pentacam HR® was 478.86±45.31µm (range: 477.20-480.53). No significant difference in TCT between the two visits (p=0.54) and measurements (p=0.63) for Visante™ OCT. For Oculus Pentacam HR®, no significant difference was found for each visit (p=0.18) but differences existed in the measurements outside of the central region (p=0.001). Tukey post-hoc analysis shows the differences (p˂0.05) were found in the +1 and +4 (supero-temporal) locations in the 135 meridian. Significant differences were found comparing the two instruments, (p<0.05). Bland Altman plots were used to demonstrate the differences between the two instruments and indicate their limits of agreement. CONCLUSION: Both instruments gave repeatable measurements as no significant differences were found in most locations in all meridians. Comparing the two instruments, they were not reproducible in all locations.

Change in over-refraction after scleral lens settling on average corneas.

PURPOSE: The purpose of this study was to determine the change in over-refraction, if any, after a scleral lens settled on the eye for 6-8 h. METHODS: Sixteen patients of varying refractive errors and normal corneal curvatures (measured with Pentacam™ Oculus) were fitted with trial Mini-Scleral Design (MSD) scleral lenses (15.8 mm diameter) in one eye. The sagittal depths of the scleral lenses were selected by adding 350 µm to the corneal sagittal heights measured at a chord length of 15 mm with the Visante™ optical coherence tomographer (OCT) anterior segment scans and picking the closest available trial lens in the set. Initial measurements were taken 30 min after lens insertion and included an auto-refraction, subjective refraction, and best sphere refraction over the contact lens. Visual acuities and Visante™ OCT anterior segment scans were also taken. These measurements were repeated after 6-8 h of lens wear. RESULTS: Over the trial wearing period, the average change in the spherical component of the over-refraction was +0.06 D (S.D. 0.17) (p = 0.16). The average change in cylinder was +0.04 D (S.D. 0.19) (p = 0.33). The average absolute change in axis was 1.06° (S.D. 12.11) (p = 0.74). The average change in best sphere was +0.13 ± 0.30 D (p = 0.12). There was no significant change in visual acuity with the best sphere over-refraction over the 6-8 h wearing period. There was a significant change in central corneal clearance over the wearing period of 83 µm (S.D. 22) (p < 0.0001). CONCLUSION: Despite a significant change in the central corneal clearance due to thinning of the fluid reservoir as the scleral lens settled (an average decrease of 83 µm after wearing the lenses for 6-8 h), there was not a statistically significant change in the subjective over-refraction (sphere, cylinder, and axis) or best sphere or visual acuity. This study has confirmed that there is no link between reduction in central corneal clearance and change in over-refraction for average corneas.

Water Exposure is a Common Risk Behavior Among Soft and Gas-Permeable Contact Lens Wearers.

PURPOSE: To understand soft contact lens (SCL) and gas-permeable (GP) lens wearers' behaviors and knowledge regarding exposure of lenses to water. METHODS: The Contact Lens Risk Survey (CLRS) and health behavior questions were completed online by a convenience sample of 1056 SCL and 85 GP lens wearers aged 20 to 76 years. Participants were asked about exposing their lenses to water and their understanding of risks associated with these behaviors. Chi-square analyses examined relationships between patient behaviors and perceptions. RESULTS: GP lens wearers were more likely than SCL wearers to ever rinse or store lenses in water (rinsing: 91% GP, 31% SCL, P < 0.001; storing: 33% GP, 15% SCL P < 0.001). Among SCL wearers, men were more likely to store (24% vs. 13%, P = 0.003) or rinse (41% vs. 29%, P = 0.012) their lenses in water. Showering while wearing lenses was more common in SCL wearers (86%) than GP lens wearers (67%) (P < 0.0001). Swimming while wearing lenses was reported by 62% of SCL wearers and 48% of GP lens wearers (P = 0.027). Wearers who rinsed (SCL; P < 0.0001, GP; P = 0.11) or stored lenses in water (SCL; P < 0.0001, GP P = 0.007) reported that this behavior had little or no effect on their infection risk, compared with those who did not. Both SCL (P < 0.0001) and GP lens wearers (P < 0.0001) perceived that distilled water was safer than tap water for storing or rinsing lenses. CONCLUSIONS: Despite previously published evidence of Acanthamoeba keratitis' association with water exposure, most SCL, and nearly all GP lens wearers, regularly expose their lenses to water, with many unaware of the risk.

Sub-micrometer axial resolution OCT for in-vivo imaging of the cellular structure of healthy and keratoconic human corneas.

Corneal degenerative conditions such as keratoconus (KC) cause progressive damage to the anterior corneal tissue and eventually severely compromise visual acuity. The ability to visualize corneal tissue damage in-vivo at cellular or sub-cellular level at different stages of development of KC and other corneal diseases, can aid the early diagnostics as well as the development of more effective treatment approaches for various corneal pathologies, including keratoconus. Here, we present the optical design of an optical coherence tomography system that can achieve 0.95 µm axial resolution in biological tissue and provide test results for the system's spatial resolution and sensitivity. Corneal images acquired in-vivo with this system from healthy and keratoconic human subjects reveal the cellular and sub-cellular structure of the corneal epithelium, as well as the normal and abnormal structure of the Bowman's membrane and the anterior corneal stroma.