Crowding changes appearance systematically in peripheral, amblyopic, and developing vision

Visual crowding is the disruptive effect of clutter on object recognition. Although most prominent in adult peripheral vision, crowding also disrupts foveal vision in typically-developing children and those with strabismic amblyopia. Do these crowding effects share the same mechanism? Here we exploit observations that crowded errors in peripheral vision are not random: target objects appear either averaged with the flankers (assimilation), or replaced by them (substitution). If amblyopic and developmental crowding share the same mechanism then their errors should be similarly systematic. We tested foveal vision in children aged 3-9 years with typical vision or strabismic amblyopia, and peripheral vision in adults. The perceptual effects of crowding were measured by requiring observers to adjust a reference stimulus to match the perceived orientation of a target ‘Vac-Man’ element. When the target was surrounded by flankers that differed by ±30°, adults and children reported orientations between the target and flankers (assimilation). Errors were reduced with ±90° differences, but primarily matched the flanker orientation (substitution) when they did occur. A population pooling model of crowding successfully simulated this pattern of errors in all three groups. We conclude that the perceptual effects of amblyopic and developing crowding are systematic and resemble the near periphery in adults, suggesting a common underlying mechanism.

Retinal Thickness and P-ERG Changes in Adult Patients With Anisometropic and Strabismic Amblyopia

Objective To investigate the changes of retinal thickness and P-ERG signals in adult patients with anisometropic and strabismic amblyopia. Methods Sixty patients with monocular adult amblyopia, including 30 anisometropic amblyopes (AA group) and 30 strabismic amblyopes (SA group), were enrolled in our study at the outpatient clinic of The Hefei First People’s Hospital Hospital of Anhui medical University from June 2019 to November 2020. Retinal nerve fiber layer (RNFL) thickness was measured within 3.4 mm diameter range surrounding the optic nerve, and ganglion cell complex (GCC) layer thickness within 6 mm diameter range surrounding the fovea by an Optovue RTVue OCT in both amblyopic and fellow eyes. The amplitude and latency of P50 and N95 in P-ERG were recorded by a Roland electrophysiology instrument under two stimulation conditions with different temporal and spatial frequencies that were designed to bias the parvocellular and magnocellular pathways respectively. Data between amblyopic and fellow eyes was statistically analyzed by paired t test. The correlation between axial length and parameters of OCT and P-ERG was examined by Pearson correlation test. Results (1) Changes in RNFL thickness: In the AA group, RNFL thickness in temporal sector was significantly thinner (p = 0.033), while that in the nasal, superior and inferior sectors increased (p < 0.05) compared with fellow eyes. In SA group, no significant difference (each sector p > 0.05) was found between amblyopic eyes and fellow eyes. (2) Changes in GCC thickness: Compared with fellow eyes, in the AA group, GCC layer thickness of amblyopic eyes was significantly increased (p = 0.039), whereas in the SA group, we did not find a significant difference between amblyopic eyes and fellow eyes (p > 0.05). (3) P-ERG stimulated mode biased the parvocellular pathway: When compared with fellow eyes (n = 15), in the AA group, the amplitudes of P50 (p = 0.004) and N95 (p = 0.038) were significantly decreased in amblyopic eyes, but no significant latent time difference (p > 0.05) was found. In the same stimulus pattern, no statistically significant difference (n = 15, p > 0.05) between amblyopic eyes and fellow eyes was found in the amplitude and latency of P50 and N95 in the SA group. (4) P-ERG stimulated mode biased the magnocellular pathway: The amplitude and latency of P50 and N95 showed no statistically significant difference (p > 0.05) in either the AA group or the SA group. (5) We found no significant correlation between axial length and OCT, P-ERG parameters (p > 0.05) in either group. Conclusion Our results showed that the alterations in structure and function of retina that could be seen in adult anisometropic amblyopia were not found in adult strabismic amblyopia group. The functional loss in anisometropic amblyopia was found to bias to a damage of partial ganglion cells by the parvocellular pathway. These findings indicated that the pathological mechanisms were different between anisometropic and strabismic amblyopia.

A Multi-Modality Treatment Approach in Vision Therapy for a Patient with Form Deprivation Adult Strabismic Amblyopia and Nystagmus: A Case Report

Background: Amblyopia is characterised by visual impairment along with compromised binocular visual function. Form deprivation amblyopia is a result of opaque media which results in obstruction of light. This obstruction of light prevents visual development. It is has traditionally been managed at early stage of life through occlusion therapy. Case Summary: A 29-year old male presented to us, diagnosed with form deprivation adult strabismic amblyopia and nystagmus. Anterior segment evaluation showed pseudophakia in both eyes, and posterior segment was within normal limits. Stereopsis was absent. In-office vision therapy and homebased vision therapy was undertaken, which included optometric syntonic phototherapy, biofeedback mechanisms to improve nystagmus along with oculomotor skills, monocular fixation in a binocular field (MFBF) and binocular therapies in-office, and Amb-iNet at home. Conclusion: A multi-modality treatment approach in vision therapy is presented, which resulted in improvement of visual acuity, stereopsis and other components of vision for an adult with form deprivation strabismic amblyopia and nystagmus.