Repeatability of the Grating Acuity Test in Advanced Retinitis Pigmentosa (RP)

Abstract

Abstract: : Purpose: To determine the variability of the Grating Acuity Test developed by Optobionics Corporation for the evaluation of visual acuity (VA) among legally blind RP subjects. Methods: Pre–operative data were collected from 20 subjects across four centers. 144 black and white square–wave gratings were individually projected onto a screen and shown for 5–second intervals to test VA ranging from 20/6400 to 20/32, in 0.1 logMAR steps, with each VA level shown 8 times per test. Gratings were presented in a pseudo–random pattern of horizontal, vertical, diagonal left or right orientation, within a circular field spanning up to 74°. Tests were repeated across three visits within one month. Testing was performed with full cycloplegia and refractive correction for the test distance. The visual acuity threshold was the highest spatial frequency grating correctly identified in at least 5 of 8 trials. Results: Preliminary analysis of the results from 5 subjects (10 eyes) indicated a mean within–visit 95% coefficent of repeatabilty of 5.3 gratings (range 3.7–8.2). The mean between–visit 95% coefficent of repeatabilty was 12.7 gratings (range 3.0–32.2). The mean number of gratings identified was 76 (range 52–108). A wide range of vision loss was evaluated, with mean VA of 1.4 logMAR (range 1.0 – 1.8). For VA, the mean CR.95 across all subjects was 0.16 logMAR (range 0–0.4). Conclusions: The Grating Acuity Test is a repeatable measure of visual acuity in subjects with legal blindness due to advanced RP, including those with severe loss of vision and limited responses to the ETDRS chart series, and will be useful to monitor outcomes in clinical trials.

Keywords: low vision • retinal degenerations: hereditary • visual acuity