A Novel Contact Lens Wettability Grading Scale Related to Changes in Visual Function

Abstract

Purpose: : The wettability of a soft contact lens (SCL) surface can be measured or graded by several methods, but none are linked to functional measures of vision. The purpose of this study was to develop a novel grading method to quantify SCL surface de-wetting related to changes in visual function.

Methods: : Ten habitual SCL wearers wore different hydrogel and silicone hydrogel SCLs during testing. Each subject kept the tested eye open for as long as possible while the tear film over the SCL was imaged via specular reflection and contrast sensitivity (CS) was simultaneously measured psychophysically through a beam splitter. The contact lens evaluation of wettability (CLEW) grading scale was developed based on disruption of the centrally located Purkinje image and texture in the specular reflection. Graded steps were related to changes in CS. To test the CLEW scale, 4 frames from each trial (spaced equally across the time of data capture) with associated CS measures were selected, randomized and graded by 2 experienced clinicians, masked to subject, trial and CS.

Results: : Grades 1 and 2 of the CLEW scale involved minor disruptions of the Purkinje image with the emergence of increasing fine surface texture, while Grades 3 and 4 showed increasing disruption of the Purkinje image. Half steps were included but are not presented here. The relative change in CS within each trial increased with CLEW grade (change in CS AVG±SD); Grade 1 (0.02±0.06), Grade 2 (0.14±0.14), Grade 3 (0.17±0.28), Grade 4 (0.45±0.35). There were significant differences in CS between grades (p<0.05, ANOVA with Bonferroni post hoc), except between Grades 2 and 3. The 2 graders showed substantial inter-rater agreement (Cohen’s kappa, 0.65).

Conclusions: : The CLEW grading scale uses images and text to describe each SCL wettability grade, relates significantly to a functional measure of vision and shows substantial reliability between clinical observers. The CLEW grading scale shows promise as an outcome measure for use in SCL clinical trials.

Keywords: contact lens • contrast sensitivity • cornea: tears/tear film/dry eye