![]() None of these studies found a clinically significant difference between the two methods, suggesting that digital and dioptric blur can be used interchangeably for clinical measures of VA.Ĭontrary to other experiments of this kind we intended to test the digital blur in a short observing distance (e.g. found comparable measurements of VA for digital and dioptric blur but, on the contrary, with a tendency for dioptric blur to result in slightly lower VA 11. found no significant difference between digital and dioptric blur, with a tendency for digital blur to result in a slightly lower VA for all but one participant 10. They also found a slight tendency for the same VA to result from a smaller amount of simulated defocus than optical defocus, although this only reached significance for one amplitude of defocus that was tested. used a similar approach to compare VA measured using real and simulated refractive errors, including spherical refractive error and astigmatism, and found that there was a high correlation between VA measured by the two methods 9. compared VA measured using source (digital) versus observer (dioptric) blur and found a high correlation between the two methods, although digital blur resulted in a lower VA, which was statistically, but not clinically, significant 8. Here, instead, we ask whether digital blurring results in the same VA as dioptric blurring by the same amount. These include a model of visual processing to estimate visual acuity based on image quality and they show good agreement with the corresponding clinical acuity measurements 3, 4, 5, 6, 7. Moreover, digital blur brings several advantages over the dioptric approach, including a low sensitivity to eyelid squinting, removal of optical setup limitations, such as the variability of the lens-to-eye distance and alignment, and overcoming the restricted set of lens powers available.Ī number of authors have described the use of simulation for predicting an individual’s visual acuity (VA) from a wavefront measurement. The advantage of our digital approach is an easy implementation using a standard office PC. While more expensive, such systems have the ability to manipulating higher-order as well as lower-order aberrations. These systems are complex, but a commercial device exists (VAO, Voptica). There are alternative and more sophisticated methods to generate the defocus at the observer side, such as using a deformable mirror or liquid crystal spatial light modulator in an adaptive optics system 1, 2. As an alternative approach, a visual image can be degraded at the position of an observer, e.g. We were interested in an approach, sometimes called a source modification, which transforms an original image at the level of generation (e.g. The aim of our study was to design an image modification procedure to simulate visual defocus. 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. 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. ![]() 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). ![]() Stimuli were observed on a PC CRT screen. To compare all three approaches, we examined VA in 10 healthy men. 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. The equivalent spherical refractive error of + 1, + 2 or + 4 D, was applied in the rendering of Landolt Rings. ![]() 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.
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