Field measures of refractive error: A comparative study

In the developing world, refractive error (RE) is a common and treatable cause of visual disability. Portable field technologies to be used by lay technicians offer the potential to overcome the problem of inaccessible eye care. Three field methods of measuring RE performed by a lay technician were compared to a gold standard procedure, subjective refraction (SR) performed by a trained eye care professional, in a randomized clinical study. 50 subjects were recruited (ages 18-29). Field measures included: (1)AdSpecs, adjustable fluid filled lenses; (2)Focometer, a self adjusted focusable telescope; (3)Predetermined Lens Refraction (PLR), a pre-scripted series of spherical lens choices. Matched Student's t-tests was used to compare mean RE determined by each method. Mean (SD) age was 24.3y (1.5). Mean RE determined by SR was -2.50 (3.2). Ten (20%) subjects were hyperopic (>0.25 D), three (6%) were emmetropic, and 37 (74%) were myopic (>-0.25D). Mean (SD) RE for AdSpecs, Focometer and PLR was -2.42 (2.68), -2.80 (2.816), -1.79 (1.76) respectively. Mean PLR RE had the greatest absolute deviation from the gold standard, 0.77D on average (p=.004). Visual acuity was corrected to 20/20 by SR, AdSpecs, Focometer and PLR in 98%, 88%, 84%, and 66% of subjects respectively. Both the AdSpecs and Focometer were able to determine RE within 0.30D when compared to the gold standard subjective refraction and thus held a statistically and clinically significant advantage over the PLR in determining RE. The AdSpecs and Focometer also held an advantage over the PLR in their ability to achieve 20/20 VA.