The purpose of this study was twofold: to verify a fast, clinically applicable method for determining off-axis refraction and to assess the impact of objectively obtained off-axis refractive correction on peripheral low-contrast visual acuity.
We measured peripheral low-contrast resolution acuity with Gabor patches both with and without off-axis correction at 20 degrees in the nasal visual field of 10 emmetropic subjects; the correction was obtained using a commercial open-field Hartmann-Shack wavefront sensor, the COAS-HD VR aberrometer. Off-axis refractive errors were calculated for a 5-mm circular pupil inscribed within the elliptical wavefront by COAS using the instruments’ inbuilt “Seidel sphere” method.
Most of the subjects had simple myopic astigmatism, at 20 degrees in the nasal visual field ranging from −1.00 to −2.00 DC, with axis orientations generally near 90 degrees. The mean uncorrected and corrected low-contrast resolution acuities for all subjects were 0.92 and 0.86 logMAR, respectively (an improvement of 0.06 logMAR). For subjects with a scalar power refractive error of 1.00 diopters or more, the average improvement was 0.1 logMAR. The observed changes in low-contrast resolution acuity were strongly correlated with off-axis astigmatism (Pearson r = 0.95; p < 0.0001), the J 180 cross-cylinder component (Pearson r = 0.82; p = 0.0034), and power scalar (Pearson r = −0.75; p = 0.0126).
The results suggest that there are definite benefits in correcting even moderate amounts of off-axis refractive errors; in this study, as little as −1.50 DC of off-axis astigmatism gave improvements of up to a line in visual acuity. It may be even more pertinent for people who rely on optimal peripheral visual function, specifically those with central visual field loss; the use of open-field aberrometers could be clinically useful in rapidly determining off-axis refractive errors specifically for this patient group who are generally more challenging to refract.
Department of Medicine and Optometry, Linnæus University, Kalmar, Sweden (PL, KB, JG); and Biomedical and X-Ray Physics, KTH, Royal Institute of Technology, Stockholm, Sweden (RR, LL, PU).
Peter Lewis Department of Optometry and Medicine SE-39182 Kalmar Sweden e-mail: email@example.com