Yixiu Zhou

Diurnal Pattern of Tear Osmolarity and Its Relationship to Corneal Thickness and Deswelling

Purpose: To identify the diurnal variations of tear osmolarity (TO) and its relationship with central corneal thickness (CCT) and corneal deswelling over a 14-hour period. Methods: TO and CCT were measured using the TearLab Osmometer and Bioptigen spectral domain optical coherence tomography, respectively, on 38 healthy neophytes (mean age, 21.5 ± 2.2 years). TO and CCT were measured at bedtime (baseline), upon awakening, 20 minutes, 40 minutes, 1 hour, 2 hours, 4 hours, and 8 hours after awakening. Deswelling rate was estimated and expressed as percent recovery per hour (PRPH). Mixed-effect linear regression models describe the relationships among TO, CCT, and PRPH. Results: The tear film upon wakening (264 ± 14 mOsm/L) was hypoosmotic compared with baseline (297 ± 15 mOsm/L, P < 0.001). TO (in mOsm/L) at 20 minutes, 40 minutes, 1 hour, 2 hours, 4 hours, and 8 hours were 287 ± 10, 292 ± 16, 293 ± 12, 292 ± 10, 289 ± 10, and 286 ± 10, respectively. CCT (mean ± SD) at baseline was 552.2 ± 35.9 µm and increased to 572.0 ± 38.7 µm after sleep. CCT returned to baseline thickness 4 hours after awakening (P < 0.000) and remained stable throughout the day. A small but statistically significant association was found between higher TO and lower CCT (P < 0.0001) and between lower baseline TO and higher PRPH (faster deswelling; P < 0.0001). Conclusions: The diurnal pattern of TO has been established. The association of TO with corneal thickness and deswelling suggests that the tear film tonicity may be partly responsible for corneal hydration control; however, the effect may not be of clinical significance in a normal study cohort.

Short-Term Effects of Overnight Orthokeratology on Corneal Epithelial Permeability and Biomechanical Properties

PURPOSE To investigate the effects of 30 nights of overnight orthokeratology (OOK) on corneal epithelial permeability (Pdc) and corneal biomechanical properties. METHODS BE Retainer and Paragon CRT lenses were used. Visits were scheduled approximately 4 hours after awakening at baseline and after 1, 5, 10, 14, and 30 days of treatment. Pdc was measured at baseline and at day 30, whereas corneal biomechanical properties and visual acuities (VAs) were measured at all visits. RESULTS Thirty-nine neophytes and soft contact lens wearers completed the study. There was no difference in Pdc between baseline (ln[Pdc] [95% confidence interval (CI)] = -2.65 [-2.80 to -2.50]) and day 30 (ln[Pdc][CI] = -2.68 [-2.85 to -2.50]) (P = 0.88). Corneal hysteresis (CH) and corneal resistance factor (CRF) reduced significantly from baseline (CH [CI] = 10.89 [10.59-11.19] mm Hg and CRF [CI] = 10.35 [9.99-10.72] mm Hg) to day 30 (CH [CI] = 10.59 [10.31-10.87] mm Hg and CRF [CI] = 9.58 [9.26-9.89] mm Hg) (P = 0.001 for CH and P < 0.001 for CRF). Posttreatment VA did not reach baseline targets, and the difference was worse with low-contrast letters. Asian individuals (n = 18) had significantly worse VA than non-Asian individuals (n = 21) under most conditions through day 5, and the difference extended through day 14 with low-contrast letters under mesopic conditions. The percentage of participants who achieved 20/20 uncorrected was 17% Asian and 40% non-Asian individuals after day 1 and reached 69% Asian and 83% non-Asian individuals at day 30. CONCLUSIONS Thirty nights of OOK did not alter Pdc when measured 4 hours after awakening. OOK caused CH and CRF to decrease, but the changes were not clinically significant compared with diseased and postsurgical cases. Asian individuals, who had lower baseline CH in this study, responded slower to OOK based on early uncorrected VA and overrefraction measurements.

Objective Quantification of Fluorescence Intensity on the Corneal Surface Using a Modified Slit-lamp Technique

Objectives: To improve the digital quantification of fluorescence intensity of sodium fluorescein instilled on corneal surface by modifying a slit lamp hardware and performing computerized processing of captured digital images. Methods: The optics of a slit lamp were modified to remove corneal Purkinje reflection and to expand the illuminated area on the cornea, followed by postexperiment image processing to minimize the influence of uneven illumination. To demonstrate the feasibility and reliability of this new technique, we applied it to objective grading of corneal staining with sodium fluorescein. The results of computerized grading were compared with the results obtained using standard subjective grading of corneal staining. Objective digital grades, staining area, and staining pixel with manually and automatically defined threshold (SP-M and SP-A) were calculated for both original and processed images. Standard subjective grades of the original images were performed by 13 trained observers using National Eye Institute (NEI), Efron, and CCLRU grading scales. A series of linear regression analyses were performed to investigate the correlation between objective and subjective grades. Results: Digital grades of the captured images were correlated significantly with subjective grades. After minimization of the artifact caused by the nonuniform illumination, correlations between digital and subjective grading were mostly strengthened. In some cases, digital grading of corneal staining was more sensitive than subjective grading methods when differentiating subtle differences of corneal staining. Conclusions: Modifications performed on commercial slit-lamp hardware and the proposed digital image–processing technique have improved the quality of captured images for semiautomated quantification of fluorescein intensity on the cornea.

Effects of Lens-Care Solutions on Hydrogel Lens Performance

SIGNIFICANCE Lens care multipurpose solutions (MPSs) can have varying effects on contact lens (CL) surface properties and the corneal epithelium. PURPOSE The aim of this study was to investigate the short-term effects of newer MPS on CL comfort and dryness, prelens tear-film stability, and ocular-surface health. In vitro study was also performed to assess the effect of MPSs on CL surface properties. METHODS Acuvue 2 CLs were soaked in control solution, Clear Care (CC), or test solutions: PureMoist, Biotrue, RevitaLens (RL), or saline solution (SS). Over four visits, subjects were exposed to control solution in one eye and to test solution in the contralateral eye for 2 hours using presoaked CLs. Contact lens comfort and dryness, ocular-surface health assessment, prelens noninvasive tear breakup time, and corneal epithelial permeability measured with fluorometry were assessed. Captive-sessile bubble technique evaluated CL wettability and viscous drag in vitro. RESULTS At 10 minutes, mean comfort ± SD with PureMoist (76 ± 22) was lower than CC (86 ± 15, P = .02), Biotrue (92 ± 9, P < .005), RL (90 ± 13, P < .005), and SS (90 ± 14, P < .005). No other difference in comfort or dryness was noted. RevitaLens was associated with greater corneal epithelial permeability than CC (P = .020) and increased corneal staining compared with all MPSs (P < .005 for all). RevitaLens was also associated with longer prelens noninvasive tear breakup than CC (P < .005). In vitro results agreed with clinical findings of tear-film stability as RL reduced viscous drag. Contact lens surface wettability was enhanced by all MPSs in comparison to SS. CONCLUSIONS Differences of MPSs on the ocular surface were found in vivo and in vitro. RL caused the greatest corneal epithelium disruption but also associated with higher tear-film stability. The effect of MPSs on CL surface properties in vitro seems to reflect how MPSs altered prelens tear stability.

Effects of corneoscleral topography on soft contact lens performance: A pilot study

To quantify corneoscleral junction (CSJ) topography in soft contact lens (SCL) wearers, and assess the association between the CSJ and SCL performance and subjective comfort, forty-four adapted SCL wearers (16 Asians, 16 Caucasians, 12 Latinos) were recruited for the present study. Corneal topography was taken with a Medmont E300 (Medmont International, Pty Ltd.). CSJ images were taken with a commercial OCT (Bioptigen, Inc.). Our published CSJ image analysis technique was used to describe the geometric properties of the CSJ using the sum of squared orthogonalized residuals (SSRo). Multivariable mixed effects models were employed to examine associations between SSRo and subject demographics, ocular characteristics, SCL fit and performance, and comfort. The SSRo was significantly related to quadrant (p < 0.001), ethnicity (p = 0.014), and horizontal corneal shape factor (p = 0.044). The nasal quadrant had the largest SSRo, indicating the steepest CSJ profile and/or the most irregular CSJ surface, followed by the inferior quadrant. The superior and temporal quadrants had the smallest SSRo, indicating relatively flat and even CSJ topography. Caucasians had the steepest and/or most irregular CSJ compared with Latinos and Asians. Less inferior-superior heterogeneity in the SSRo was associated with greater comfort after 6 h of lens wear. The SSRo was proved to be a useful tool to quantify CSJ geometry in SCL wearers. Significant differences in the SSRo were found among quadrants and ethnic groups. Better subjective comfort after 6 h of SCL wear was associated with a smaller difference in the SSRo between the superior and inferior quadrants.