Elevated Visual Crowding in CRB1-Associated Retinopathies: Understanding Functional Visual Deficits Using Child-Friendly Computerized Testing

PURPOSE: Mutations affecting the CRB1 gene produce retinal dystrophies including early onset severe retinal dystrophy/Leber congenital amaurosis (EOSRD/LCA), retinitis pigmentosa (RP), cone-rod dystrophy (CORD), and macular dystrophy (MD). As treatment strategies advance toward clinical translation, there is a need to establish reliable outcome metrics and to better understand the visual deficits associated with CRB1 retinopathies. To this end, we measured visual acuity (VA) and crowding (the disruptive effect of clutter on object recognition), both key functions in spatial vision, using child-friendly computer-based tests, and gold-standard clinical measures. METHODS: Patients with molecularly confirmed biallelic CRB1 pathogenic variants were compared with age-matched controls (n = 20 in each). Best-corrected visual acuity (BCVA) was measured with both Early Treatment Diabetic Retinopathy Study (ETDRS) and the computerized VacMan procedures (using an unflanked/isolated VacMan target), which also allowed measurement of crowding when surrounding flanker elements were added. RESULTS: Both acuity and crowding were significantly elevated in individuals with CRB1 retinopathy compared with controls. ETDRS acuity correlated with both the unflanked (r = 0.868, P < 0.001) and flanked VacMan thresholds (r = 0.748, P < 0.001). No statistically significant changes in crowding were observed with respect to CRB1 phenotype (EOSRD/LCA, CORD, or MD) or age of onset. CONCLUSIONS: This study demonstrates for the first time that individuals with CRB1 retinopathy exhibit elevated crowding in their foveal vision compared with controls. Measuring crowding offers valuable insights into understanding functional visual deficits in CRB1 retinopathy and could be a useful metric for monitoring disease progression and treatment outcomes in inherited retinal diseases.