Contour interaction in the presence of congenital nystagmus

Abstract

Using a computer-generated acuity task, the resolution of vertical and horizontal Landolt Cs was assessed at three levels of contrast, each for three different crowding conditions. Eighteen adults participated; six had congenital idiopathic nystagmus, six were oculocutaneous albinos and six served as controls. Contour interaction was evident when bars were placed 1 gap-width from the Landolt C and was more marked as contrast increased. When scaled to the individual resolution limit, the magnitude of contour interaction displayed by the albinos was not significantly different from the controls, however the idiopaths did exhibit a greater crowding effect than the controls. These results imply that fixation instability is a contributory factor in contour interaction, but only when retinal image velocity is above a certain threshold.

A systematic review on ‘Foveal Crowding’ in visually impaired children and perceptual learning as a method to reduce Crowding

“…Five of these were conducted in a population of children with NV [7,20-22] and two were conducted in a population of VI adults [8,9]. Often, the distances over which contour interaction occurs are expressed in steps of the Minimum Angle of Resolution (MAR).…”

“…There were two studies on contour interaction in VI adults [8,9] (see Figure 3). One study compared the full contour interaction area, the point of maximum contour interaction, and the peak magnitude of contour interaction between adults with NV and adults with congenital nystagmus (CN)[9].…”

“…One study compared the full contour interaction area, the point of maximum contour interaction, and the peak magnitude of contour interaction between adults with NV and adults with congenital nystagmus (CN)[9]. Another study focused on the area at which contours caused maximum interaction effects and compared between three subject groups: adults with NV, adults with albinism and adults with CN [8]. Both studies found an increased amount of contour interaction in adults with CN when compared to controls.…”

“…This overview focuses on three groups that show excessive degrees of foveal crowding when compared to adults with NV: (1) children with NV, in this group foveal crowding is present until at least 11 years of age [7], (2) VI children and adults [8-10] and (3) children with a cerebral visual impairment (CVI) [6,11]. In VI individuals, foveal crowding seems to persist much more and much longer than in individuals with NV [10].…”

Clinical Contrast Sensitivity Function in Patients with Infantile Nystagmus Syndrome Before and After Eye Muscle Surgery

“…Visual function in patients with INS is affected by unpredictable combinations of ocular motor (eccentric null zones, damping with convergence, monocular intensity changes, periodicity, strabismus, poor smooth pursuit, OKN and attentional changes) and sensory system defects (ammetropia, amblyopia, photosensitivity, loss of contrast sensitivity, poor motion perception, decreased temporal luminance, impaired contour interaction, light interference and pre-chiasmal, chiasmal, post-chiasmal and maldevelopment) [22][23][24][25][26][27]. Visual functions directly affected include high spatial acuity vision, contrast sensitivity, motion detection, visual recognition time, gaze and time dependent vision, depth, stereopsis, smooth pursuit, vestibular and proprioceptive functions [23,[28][29][30][31][32].…”