Abstract
BACKGROUND: This explorative study investigated procedures for the self-assessment of spherocylindrical refractive errors. METHODS: Eighteen participants with a mean age of 34.0 ± 8.8 years were enrolled. Adjustable Alvarez lenses were mounted in a rotatable ring holder and two procedures were tested for the self-adjustment: (1) rotation of the lens in three meridians: 0°, 60° and 120° and (2) rotation of the optotypes in the same meridians. Starting from maximum positive power, the participants were required to decrease the power of the Alvarez lens until the optotypes (0.0 logMAR) appeared to be clear the first time. Best-corrected visual acuity (BVA) was measured using a psychophysical staircase procedure. Bland-Altmann analysis was carried out in order to calculate the limits of agreement between the self-refraction method and the standard subjective refraction. RESULTS: Using procedure 1, 77 per cent of the subjects achieved a VA ≥ 0.1 logMAR (6/7.5) and the same was true for 88 per cent of the subjects using procedure 2. Using procedure 1, a significantly worse BVA was found, when compared to subjective refraction (ΔVA = -0.15 logMAR, F(3,140) = 7.11, p = 0.046, median test). Analysis of variance (ANOVA) analysis showed a significant influence of the refraction method on the oblique astigmatism component J(45) but not for the spherical equivalent M and the straight astigmatism component J(0) (M: F(3,140) = 0.532, p = 0.661; J(0) : F(3,140) = 0.056, p = 0.983; J(45) : F(3,140) = 13.97, p < 0.001; ANOVA). The limits of agreement for the spherical equivalent error M were ± 1.10 D and ± 1.20 D and for the astigmatic components J(0) ± 0.78 D and ± 0.59 D and for J(45) ± 0.62 D and ± 0.54 D, for procedure 1 and procedure 2, respectively. CONCLUSIONS: Fixed adjustable Alvarez lenses and rotatable stimuli can provide a fast and precise self-assessment method to measure the spherocylindrical error of the eye.