Short-Term Corneal Endothelial Response to Wear of Silicone-Hydrogel Contact Lenses in East Asian Eyes

Corneal Endothelial Blebs Induced in Scleral Lens Wearers

SIGNIFICANCE

In the bleb phenomenon, some endothelial cells transiently lose their specular reflection. This has been reported during contact lens wear and goggle-induced hypoxia or hypercapnia.

PURPOSE

The purposes of this study were to determine whether blebs appear after scleral lens wear and if their appearance is influenced by lens clearance and to compare bleb and cell sizes.

METHODS

Twenty-one subjects were fitted with two similar scleral lenses with different targeted clearances of 200 and 400 μm (the SL200 and SL400, respectively). Each lens was worn unilaterally for 25 minutes, whereas the other eye served as a control. Before and after lens wear, the endothelium was photographed using specular microscopy. The number of blebs and measurements of the areas of cells and blebs were analyzed. Paired t tests compared differences in the areas of cells and blebs. Differences in median bleb number were evaluated using the Wilcoxon test.

RESULTS

After wearing the SL200 and SL400 lenses, respectively, 9 and 14 subjects had at least one bleb. The median bleb number after wearing lenses was significantly different (SL200, 0.00; SL400, 1.00; P = .02). Bleb and cell areas were significantly different (blebs, 293 ± 28; cells, 370 ± 32 μm; P < .0001).

CONCLUSIONS

After 25 minutes of wearing scleral lenses with each of the two targeted clearances, SL400 induced significantly more blebs than did SL200, suggesting evidence of reduced oxygen and/or increased carbon dioxide levels under scleral lenses fitted with excessive clearance. Blebs may occur more in smaller cells.

Corneal Swelling with Cosmetic etafilcon A Lenses versus No Lens Wear

Purpose

To determine if the use of pigments or adding polyvinyl pyrrolidone during the fabrication of 1-DAY ACUVUE DEFINE (AD) brand contact lenses impacts open-eye corneal swelling compared with no lens wear (NLW).

Methods

A partial double-masked, randomized, bilateral crossover study was conducted in 24 Asian subjects using AD, 1-DAY ACUVUE DEFINE with Lacreon (ADL), NLW, and a control lens with no tint (1-DAY ACUVUE MOIST [AM]). Central corneal thickness was measured before insertion and immediately after removal after 8 ± 1 h of open-eye wear using an optical pachymeter in one eye. Corneal thickness along a 10-mm cord was measured in the contralateral eye using the Visante optical coherence tomographer (OCT). Corneal swelling was tested for noninferiority using a 5% margin. The endothelial bleb response was measured at baseline and 20 min after lens insertion using specular microscopy. Subjective grading of corneal staining and limbal/bulbar hyperemia were also monitored.

Results

After 8 ± 1 h of open-eye wear, central corneal swelling across the study lenses with either optical pachymeter or OCT methods was negligible. Peripheral corneal swelling least-square mean differences with OCT were −0.03% (95% confidence interval [95% CI], −0.65 to 0.58%) and −0.26% (95% CI, −0.87 to 0.36%) between AD and ADL and the control lens (AM), respectively, and 1.67% (95% CI, 1.06 to 2.29%) and 1.45% (95% CI, 0.84 to 2.06%) between AD and ADL and NLW, respectively. No endothelial blebs were observed. No clinically significant differences were distinguished between the lenses and NLW for corneal staining and limbal/bulbar hyperemia.

Conclusions

After 8 ± 1 h of open-eye wear, central and peripheral corneal swelling along the horizontal meridian with AD, ADL, AM, and NLW were equivalent. These results confirm that the addition of polyvinyl pyrrolidone or pigments to etafilcon A to obtain a limbal ring design have no impact on corneal swelling or limbal/bulbar hyperemia during normal open-eye wear.

A powerful test for Balaam's design

The crossover trial design (AB/BA design) is often used to compare the effects of two treatments in medical science because it performs within-subject comparisons, which increase the precision of a treatment effect (i.e., a between-treatment difference). However, the AB/BA design cannot be applied in the presence of carryover effects and/or treatments-by-period interaction. In such cases, Balaam's design is a more suitable choice. Unlike the AB/BA design, Balaam's design inflates the variance of an estimate of the treatment effect, thereby reducing the statistical power of tests. This is a serious drawback of the design. Although the variance of parameter estimators in Balaam's design has been extensively studied, the estimators of the treatment effect to improve the inference have received little attention. If the estimate of the treatment effect is obtained by solving the mixed model equations, the AA and BB sequences are excluded from the estimation process. In this study, we develop a new estimator of the treatment effect and a new test statistic using the estimator. The aim is to improve the statistical inference in Balaam's design. Simulation studies indicate that the type I error of the proposed test is well controlled, and that the test is more powerful and has more suitable characteristics than other existing tests when interactions are substantial. The proposed test is also applied to analyze a real dataset.