Abstract
Purpose :
Subjective refraction (SR) is a routine procedure in eye care practice that has not evolved much in decades and is still cumbersome for patients and practitioners. Here we present a quick method to obtain a more accurate estimation of the optimal spherical equivalent, valid in presence of astigmatism, unsupervised and without paralyzing accommodation
Methods :
We use SimVis Gekko (2EyesVision, Madrid), that projects an optotunable lens onto the pupil’s eye, to generate defocus waves (periodic variations of optical power causing periodic variations in retinal blur) with frequency 15Hz, amplitude 0.75D and variable offset (-1 to +1D). Subject’s task is to adjust the offset (staircase with coarse -0.25D- and fine -0.1D- steps) until flicker in the retinal image through SimVis is minimum, happening when the blur is symmetric at both sides of the best SR. Due to interactions of the wave with the chromatic aberration of the eye, color artifacts appear outside the best SR: bluish halos on the myopic side, and reddish on the hyperopic, providing a strong cue for the direction of focus. Using a specific stimulus of black dots pattern on a magenta (blue+red) background chromatic effects are highlighted. Both flicker and chromatic cues are intuitive for the subject and minimum in the best SR, providing an easy task barely affected by astigmatism and accommodation (disrupted by the defocus wave, without cyclopegic).
4subjects (26 to 46 yo) with free accommodation provided their best SR, with staircases starting from 20 random myopic or hyperopic power offsets. They also performed traditional SR from blur detection, without defocus wave, with an equivalent black-on-white target using similar staircases in the same conditions and set-up. Measurements were performed with glasses, with and without astigmatism
Results :
The new method provided convergence of the staircases, high sensitivity and high accuracy to capture and estimate best SR: average SD of 0.11D without astigmatism, 0.14D with astigmatism. The number of staircase steps was 9±4 (each step lasting 1-5s). Traditional SR showed high uncertainty: average SD of 0.44D without astigmatism, 0.52D with astigmatism
Conclusions :
Direct subjective refraction with defocus waves shows a 4-fold improvement in the accuracy of SR in accommodating subjects. Quick (<1min) and easy for the patient, it can be directly applied to clinical practice. The procedure can be extended to the measurement of astigmatism
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.