Alternative Methods of Refraction: A Comparison of Three Techniques

Abstract

In the developing world, refractive error is a common untreated cause of visual impairment. Lay people may use portable tools to overcome this issue. This study compares three methods of measuring spherical refractive error (SE) performed by a lay technician to a subjective refraction (SR) in a controlled clinical setting and a field trial. Fifty subjects from Boston, MA (mean age, 24.3 y ± 1.5) and 50 from Nicaragua (mean age, 40 y ± 13.7) were recruited. Measures (performed on right eye only) included (1) AdSpecs, adjustable spectacles; (2) Focometer, focusable telescope; (3) Predetermined Lens Refraction (PLR), prescripted lens choices; (4) SR. Examiners were masked and techniques randomized. Student t-test compared mean SE determined by each method (95% confidence intervals). AdSpecs repeatability was evaluated by repeating measures of SE and visual acuity (VA). Mean (SD) SE for Boston subjects determined by SR was -2.46 D (3.2). Mean (SD) SE for AdSpecs, Focometer -2.41 D (2.69), -2.80 D (2.82). Among the 30 Boston subjects considered in analyses of PLR data (see Methods), PLR and SR obtained mean (SD) values of -0.65 D (1.36) and -0.41 D (1.67), respectively, a statistically significant difference of -0.24 D (p = 0.046, t = 2.09). Mean PLR SE had greatest deviation from SR, 0.67 D. 20/20 VA was achieved by SR, AdSpecs, Focometer, and PLR in 98, 88, 84, 96% of subjects. Mean (SD) SE for Nicaragua subjects determined by SR was +0.51 D (0.71). Mean (SD) SE for AdSpecs, Focometer, and PLR was +0.68 D (0.83), +0.42 D (1.13), +0.27 D (0.79). Mean PLR SE had the greatest deviation from the SR by 0.24 D, which was a statistically significant difference. 20/20 VA was achieved by SR, AdSpecs, Focometer, and PLR in 78, 66, 66, 88% of subjects. Repeated measures by AdSpecs were highly correlated. Although the mean value obtained by each technique may be similar to that obtained by SR, substantial and clinically meaningful differences may exist in some individuals; however, where SR is unavailable they could be a feasible alternative.