Comparison between optical and digital blur using near visual acuity

Abstract

In a low-cost laboratory setup, we compared visual acuity (VA) for stimuli rendered with Zernike aberrations to an equivalent optical dioptric defocus in emmetropic individuals using a relatively short observing distance of 60 cm. The equivalent spherical refractive error of + 1, + 2 or + 4 D, was applied in the rendering of Landolt Rings. Separately, the refractive error was introduced dioptrically in: (1) unchanged Landolt Rings with an added external lens (+ 1, + 2 or + 4 D) at the subject's eye; (2) same as (1) but with an added accommodation and a vertex distance adjustment. To compare all three approaches, we examined VA in 10 healthy men. Stimuli were observed on a PC CRT screen. For all three levels of refractive error, the pairwise comparison did not show a statistically significant difference between digital blur and accommodation-plus-vertex-distance-adjusted dioptric blur (p < 0.204). The best agreement, determined by Bland–Altman analysis, was measured for + 4 D and was in line with test–retest limits for examination in the clinical population. Our results show that even for a near observing distance, it is possible to use digitally rendered defocus to replicate dioptric blur without a significant change in VA in emmetropic subjects.

Effects of Perceptual Learning on Deprivation Amblyopia in Children with Limbal Dermoid: A Randomized Controlled Trial

“…LD patients after keratoplasty exhibited obvious VA and CSF deficits compared with the normal children, and these conditions may have been caused by astigmatism and surgical alterations. Hussein et al have identified that a preoperative and postoperative astigmatism that is greater than 1.5 D is a risk factor for amblyopia, which may be caused by media opacities, corneal suture, or corneal rejection action [ 14 ]. The mean spherical and astigmatic refractive errors in our participants were −3.8 ± 3.7 D and −4.9 ± 2.9 D, respectively, which were deemed to be associated with a high risk of amblyopia; thus, our patients might develop amblyopia.…”

“…The patients in the LD group underwent monocular and binocular VA assessments and a quick CSF (qCSF) assessment at full optical correction after a routine ophthalmic examination. In the N group, the children were subjected to VA and CSF assessments under two conditions, that is, full refractive correction and full refractive correction plus optical defocus (+1.00 D to +6.00 D positive spherical lens) on the right eye, with the vision of the left eye unaltered [ 14 , 15 , 16 , 17 ]. Specifically, optical defocusing was used to simulate monocular blurred BCVA in the LD group.…”

Can motion onset VEPs see through the blur?

“…In our study, the simulation of second-order aberration ("defocus" -𝑍 2 0 ) was induced as described in a study by Kordek et al 2021 13 . Thus, the resulting defocused checkerboards (of both angular sizes) were produced by computer convolution of the defocused checkerboards and the point spread function (PSF) described in [14][15][16] , which for the case of 𝑍 2 0 aberration is given by equation ( 1) 13 ,…”

“…51-BL, M.S.D. in front of the eye under examination, analogous to the methodology used in our previous study 13 .…”

Rendering algorithms for aberrated human vision simulation

“…Despite the existence of physical devices that carry out such tasks, as noted by Kordek et al [69], computer-based acuity simulations provide some important advantages over clinical approaches. Simulations are not hampered by optical setup limitations, requiring only a comparatively inexpensive desktop computer, reducing the impact of eyelid squinting.…”