Abstract
Purpose :
To study the refractive error measurement with the Direct Subjective Refraction (DSR) method by simulating the images projected on the retina. In DSR, a bichromatic image is presented and a rapid alternating defocus of ±0.25D is induced. The task of the subject is to minimize the flicker of the images perceived so that all colors flicker the same amount. The method has shown to be faster and more repetitive than traditional refraction but the reason for this has not been fully determined.
Methods :
Eye wavefront aberrations and the defocus caused by the average longitudinal chromatic aberration were used to generate the polychromatic point spread function (PSF) at the stimulus wavelengths (450 and 700nm) for a 6-mm pupil. The retinal image was obtained convolving the stimulus at each wavelength with its corresponding PSF. The root mean square contrast was used as image quality metric, IQ. In the monochromatic flicker minimization task, we assumed that the perceived IQ was the average, IQavg, that the image similarity was related to the IQ difference, ΔIQ, and that the metric maximized by the subject was a linear combination of the two FM=IQavg+(1-ΔIQ). In the polychromatic flicker minimization task, the cue that all colors flicker equally was calculated with the increase in FM, PFM=ΔFM. The through-focus metric with a monochromatic image and a static defocus, similar to the blur minimization task of the traditional refraction, and with mono and polychromatic images with alternating defocus of ±0.25D were compared through the peak width at 90% value.
Results :
The through foucs IQ, FM and PFS metrics were maximum at the nominal refraction. The image similarity metric was maximum at the nominal refractive error and decreased to increase again after 2 D, as expected due to the similarity between the PSFs at ±0.25D of those values. Peak width was 0.60 D in the blur minimization task, 0.40 D in the mono, and 0.32 D in the polychromatic flicker minimization task. The model was extended to astigmatism with a different stimulus and pupil dependence resulted smaller for FM and PFM.
Conclusions :
Despite the simplifications, the peakwidth found with the developed models is comparable to the repeatability reported in previous studies with both the traditional and the DSR method. The model explains the improvement in repeatability found experimentally and can help to identify the influence of other design parameters.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.