Abstract
Visual scenes encompass multiple depth planes forcing the visual system to constantly process defocus in the retinal image. Defocus can be useful to drive accommodation or contribute to depth perception, but it is also the most prevalent contributor to poor spatial vision. In addition to accommodation, sensory processes may also seek to reduce the overall perception of blur, especially if defocus is mismatched between the eyes (anisometropia). This experiment aimed to determine blur detection thresholds and supra-threshold perception of blur in simulated anisometropia. It also investigated how higher order aberrations interact with defocus perceptually. Simulated retinal images were presented binocularly to optically-corrected and visually normal observers with a dual-screen mirror haploscope. Image simulations were independently generated for each eye with Fourier optics software (pupil diameter of 5 mm, Stiles-Crawford apodization). Using through-focus peak image quality as a reference image, subjects adjusted the spherical defocus in one or both eyes until the image was “just noticeably blurry”. This was repeated 10 times in each condition (left eye defocus, right eye defocus or bilateral defocus). Anisometropic defocus thresholds (mean (+/− SD) = 0.472D ± 0.183D) were more than twice the bilateral defocus thresholds (0.219D ± 0.104D). In the presence of opposite-signed spherical aberration (0.2 microns), subjects tolerated nearly twice as much defocus (mean ratio = 1.87 ± 0.45) though peak image quality was considerably lower. This increase in blur tolerance will be discussed in the context of monocular and binocular neural blur suppression and also the effect it may have in targeted therapeutic anisometropia, such as monovision.