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Sarah Waugh, Denis Pelli, Leticia Álvaro, Monika Formankiewicz; Crowding distance in healthy children.. Journal of Vision 2018;18(10):855. doi: https://doi.org/10.1167/18.10.855.
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Clinically, visual acuity is measured under "crowded" conditions to enhance inter-ocular acuity differences, thereby improving detection of amblyopia. A new clinical test (Pelli, Waugh, Martelli et al, 2016) measures the crowding distance (aka "critical spacing") anywhere in the visual field, including the adult fovea, where it is smaller (0.05 deg) than a 0.0 logMAR Sloan letter. There is a need to find out how crowding distance changes with normal development, to allow screening children for abnormal development of this key property of object recognition. Crowding distance and visual acuity were measured in 200 primary school children (3-11 years) and 16 adult participants, using 9-optotype forced-choice trials and an adaptive staircase. Crowding distance was determined for trigram (AXA) and repeated arrangements (AXAXAXA…) of the Pelli font. The ratio of horizontal spacing:optotype width was maintained at 1.4x, so size and spacing co-varied. From age 3 years to young adult, crowding distance dropped four-fold, from 0.22±0.03 to 0.05±0.01 deg (mean±SE) with normal development; whereas isolated letter acuity changed only two-fold from 0.10±0.05 to -0.22±0.03 logMAR (i.e. log 2 = 0.3 = 0.1 to -0.2). Crowding distance reached adult levels at age 8 years, slightly later than the 6 years for visual acuity. In normal children, the repeated arrangement yielded a similar crowding distance to the trigram, and its immunity to eye position may help in estimating crowding distance in children and adults with poor fixation. These estimates of normal crowding distance may allow enhanced screening of children for vision problems including amblyopia.
Meeting abstract presented at VSS 2018
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