Exploring standard and low luminance visual acuity and the Moorfields Acuity Chart as outcome measures in inherited retinal disease.

INTRODUCTION

Standard visual acuity (VA) is often insensitive to subtle changes in vision that result from inherited retinal disease. Low luminance VA (LLVA) has grown in popularity as an alternative acuity measure. A new test, the Moorfields Acuity Chart (MAC) has been designed as a more sensitive and repeatable test for use in patients with age-related macular degeneration. The study explores the utility and repeatability of standard VA, LLVA and the MAC in a mixed cohort of patients with inherited retinal disease.

METHODS

Participants were recruited as part of the visual function in retinal degeneration study (Ethics Reference 20/WM/0283). Standard VA was obtained using the Early Treatment of Diabetic Retinopathy study (ETDRS) chart placed at 4 m. LLVA was obtained using the same ETDRS chart with the addition of a 2.0-log unit neutral density filter. MAC VA was obtained using standard clinic room lighting. All participants completed repeated testing.

RESULTS

Thirty-five patient participants and 36 healthy controls, with logMAR 1.00 (6/60) or better, completed testing. Both LLVA and MAC VA were reduced compared to standard VA in patient participants and healthy controls (linear mixed model: p < 0.001). All three acuity tests show comparable sensitivity, specificity and repeatability. A subset of participants (patient participants n = 34, healthy controls n = 35) completed microperimetry. Post hoc analysis of microperimetry volume sensitivity correlated significantly with all of the acuity tests and showed no significant difference in the gradient of the slopes. This suggests that VA, LLVA and MAC VA decline at a consistent rate with disease progression.

CONCLUSION

All three acuity tests could be considered viable outcome measures for clinical trials. For patients with early to moderate inherited retinal disease (logMAR 1.00 (6/60) or better), no single acuity chart appeared significantly beneficial.