Individual VA varies in AMD patients

Visual acuity (VA) in age-related macular degeneration (AMD) patients may vary significantly between measurement sessions, according to study results published in the October 2008 issue of Investigative Ophthalmology & Visual Sciences.

Praveen J. Patel, of Moorfields Eye Hospital, London, UK and colleagues used Early Treatment of Diabetic Retinopathy Study (ETDRS) charts to measure VA in non-treated AMD eyes (n=107) at four points over a 12-week period. Of the 90 eyes from which the team analysed data, 29 were early-stage AMD, displaying only small to intermediate drusen, and 25 were late-stage, demonstrating macular scars or geographic atrophy.

Among the early-stage eyes, the 95% coefficient of repeatability (CR) was nine letters on the ETDRS charts; for late-stage eyes, the CR was 17 letters. Overall CR was 12 letters. A reduction of ≥5 letters at visit one verses baseline was seen in 11% of eyes (n=10). The VA measurements of seven eyes were excluded due to independent factors affecting measurements, after which the revised CR was 10 letters for the cohort and 11 letters for the late-stage group.

Thus the team concluded that the variations in measurements they noted could have been caused by factors related either to the disease itself or to the measurement method employed, and that this could have implications for future AMD trial designs.