Other refraction systems such as retinoscopy, autorefraction, wavefront refraction, and automated subjective refraction have also been previously compared with the gold standard refraction. For noncycloplegic retinoscopy, Jorge et al.
35 found 95% limits of agreement of ±0.65 D (interval of 1.30 D) in a sample of 192 healthy adults; similarly, Ciuffreda and Rosenfield
14 obtained 95% limits of agreement of ±0.84 D (interval of 1.64 D) in a sample of 50 participants. For autorefraction, there exist many comparison studies
3,7,12,14,25–27,29,31,35–37 because there are many different commercial autorefractometers. The 95% limits of agreement ranged from ±0.31 D (interval of 0.62 D)
25 to ±1.47 D (interval of 2.94 D).
14 The wide range of limits of agreement found in all these studies can be explained because of the differences in optical principles (e.g., Scheiner, retinosocopy, image size, and best focus, among others
10) as well as the differences in study design (e.g., an average of three consecutive readings or just one reading) and sample sizes (from 12 up to 192 participants). Analogously to autorefraction, for wavefront sensor refractometers there are many validation studies
7,12,14,37,38 and the 95% limits of agreement ranged from ±0.56 D (interval of 1.12 D)
14 to ±1.04 D (interval of 2.08 D).
12 Finally, automated subjective refraction is not as popular as objective refraction systems; however, there exist a few studies,
25,27,29,36,38,39 each with a completely different automated algorithm, that found 95% limits of agreement between ±0.52 D (interval of 1.04 D)
38 to ±1.20 D (interval of 2.40 D).
39 Our results (and others) indicate that automated refraction techniques with devices such as the VAO are promising areas for applying artificial intelligence and algorithms for improving prediction of visual outcomes.