Foveal crowding differs in children and adults.

We used custom-designed acuity tests to compare the magnitude and extent of crowded letter recognition in children and adults. Visual acuity (logMAR) was measured monocularly in children and adults using five custom-designed letter tests with varying degrees of crowding: single letter, single letter surrounded by four flanking bars, single letter surrounded by four flanking letters, line of five letters surrounded by flanking bars, and line of five letters surrounded by flanking letters. The tests were constructed using Sloan letters and presented on an iPad (Apple Incorporated, Cupertino, CA) at 4 m using a standardized endpoint and instructions. Crowded logMAR was normalized to unflanked logMAR and results were analyzed in three groups: younger children aged 4-6 (n = 32), older children, aged 7-9 (n = 30), and adults (n = 27). Both groups of children showed a greater extent of crowding than the adults. The adult participants showed no difference in performance between single or linear presentation and letter or bar flankers. Letter flankers and linear presentation individually resulted in poorer performance in the younger children p < 0.001 and p = 0.003, respectively (mean normalized logMAR 0.17 in each case) and together had an additive effect (mean 0.24), p < 0.001. Crowding in the older children was adult-like except in the linear presentation with letter flankers, p < 0.001. These results indicate that both target-flanker similarity and linear presentation contribute more to foveal crowding in young children than in adults.