In how far depends our finest sense of visual space - like visual acuity and hyperacuity - on the quality of the retinal image and the sampling by the photoreceptor mosaic?
Is hyperacute vision affected by optical constraints set by the imperfections of our eyes? We tested this by measuring ocular wavefront aberrations and visual acuity thresholds in 32 young adults. Behavioral testing was performed under natural viewing conditions, while subjects wore their habitual correction (spectacle or contact lenses).
Optical measurements (ocular/corneal aberrations and axial length) were performed in a cooperation with the Eye Research Institute, Maastricht (ERIM), visual acuity and hyperacuity thresholds were obtained with a modified version of the Freiburg Visual Acuity and Contrast Test (FrACT). Wavefront errors had to be re-scaled according to the actual pupil sizes during behavioral measurements. Therefore, pupil size was constantly monitored by a custom made video-pupillometry system, based on Frank Schaeffel's 'Black Pupil Tracker' (see photo on the right).
Ocular aberrations vs. visual acuity and hyperacuity
Reiniger JL, Lobecke AC, Sabesan R, Bach M, Verbakel F, de Brabander J, Holz FG, Berendschot TTJM, Harmening WM (2019) Habitual higher order aberrations affect Landolt but not Vernier acuity. Journal of Vision, 19(5): 1-15 [doi:10.1167/19.5.11]
We find that Landolt acuity thresholds were significantly better in eyes with low higher order aberrations and high visual Strehl ratios, and significantly positively correlated with axial length. A retinal image quality metric, calculated as two-dimensional correlation between perfect and actual retinal image, was also correlated with Landolt acuity thresholds. No such correlations were found with Vernier acuity performance. Based on these results, hyperacuity thresholds are, contrary to resolution acuity, not affected by higher order aberrations of the eye.