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22-12-2011 | Article

Autorefraction ‘no substitute’ for manual VA test


Free abstract

MedWire News: Measurement of visual acuity (VA) in patients with Type 2 diabetes tends to be slightly worse with autorefraction than with manual refraction, a test-retest variability study shows.

"The results suggest that, with current instruments, autorefraction is not an acceptable substitute for manual refraction for most clinical trials with primary outcomes dependent on best-corrected VA," say study co-author Haijing Qin (Jaeb Center for Health Research, Tampa, Florida, USA) and colleagues.

For many years, clinical research studies have used the Early Treatment Diabetic Retinopathy Study (ETDRS) testing method for standardizing refraction and subsequent measurement of VA - an outcome measure in clinical research for diabetic eye disease.

An alternative method is autorefraction, which uses a computer-controlled device to provide an objective measure of an individual's refractive error without the need for a skilled refractionist.

In this multicenter study, Qin et al compared VA scores obtained after autorefraction with those obtained after manual refraction (MR-EVA) in patients with and without center-involved diabetic macular edema (DME) across a diverse range of clinical sites, autorefractors, and certified refractionists with varying levels of experience.

Testing order was randomized, study participants and VA examiners were masked to refraction source, and a second test using an identical supplemental manual refraction (MR-EVAsuppl score) was performed to determine test-retest variability.

Qin et al report that in 878 eyes of 456 study participants, the median MR-EVA score was 74 (Snellen equivalent, approximately 20/32). The spherical equivalent was often similar for manual refraction and autorefraction (median difference, 0.00; 5th-95th percentile range, -1.75 to 1.13 diopters).

However, on average, the MR-EVA scores were slightly better than the AR-EVA scores, across the entire VA range. Furthermore, the variability between the AREVA scores and the MR-EVA scores was substantially greater than the test-retest variability of the MR-EVA scores.

"Although, in general, autorefraction may not be an acceptable substitute for manual refraction, specific elements of the study design, including increased sample size and nonreliance of treatment algorithm on small differences in VA, may allow limited substitution of autorefraction for manual refraction in some studies," Qin et al conclude in the Archives of Ophthalmology.

By Andrew Czyzewski