Development of a New Scale for Ocular Surface Staining Based on Psychophysical Principles

Abstract

Purpose : Many scales have been developed to assess staining by vital dyes in dry eye (DE) and other ocular surface conditions. The attributes of these scales have typically been assigned using scientific and clinical expertise. In this study, we apply psychophysical scaling principles to develop photographic scales for the assessment of ocular surface staining for DE and related conditions.

Methods : Subjects with non-infectious ocular surface staining were enrolled at 5 clinical sites. They completed the Dry Eye Questionnaire (DEQ-5). Following instillation of 5µl of 2% fluorescein, photographs of corneal staining were taken every 30 sec for at least 5 mins. The same procedure was followed for conjunctival staining after instillation of 2µl of 1% lissamine green. Photographs were collected from 142 subjects (81% female), with an average age of 58±17 years; 89% were diagnosed with a DE. Two investigators selected a subset of the best bulbar and corneal staining images (~100) that were anonymized and a spectroradiometer was used to measure photometric measures (luminance, chromaticity). The representative cornea and conjunctival images were scaled psyschophysically by 5 clinical dry eye experts, so that the physical separation of photographs (maximum being 2m) represented staining intensity, and when completed, the position of each photograph was read off to the nearest 5mm.

Results : There was a monotonic relationship between physical measurements and psychophysically scaled staining intensity of both corneal (fluorescein) and bulbar (lissamine green) staining. Michelson contrast and u’ (chromaticity) accounted for 66% and 64% % of the variability in the psychophysically scaled images of fluorescein corneal and lissamine green conjunctival staining, respectively. These monotonic functions were used to select exemplar images of a 0 to 5 point scale by a focus group with clinical expertise. There were statistically significant correlations (r=0.36-.47, p<0.0087; Pearson’s) between corneal staining measured by the 0-5 point scale and DEQ-5 individual symptoms and total score.

Conclusions : We developed photographic grading scales of ocular surface staining based on psychophysical and photometric measures. It is the first physical and psychophysical scale to be developed for the grading of ocular surface staining, for which there remains no “gold standard” scale.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.