Objective: To quantify an apparent nasotemporal asymmetry in the location of retinopathy of prematurity with respect to the optic disc. Methods: Twenty-four-bit color images were captured using a contact digital fundus camera during routine screening. Semiautomated measurements were undertaken to determine the distance between the optic disc and retinopathy located in the nasal and temporal regions of the retina. Results: Forty-nine image pairs (17 right eye, 32 left eye) were captured from 10

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... nfants during a period of 32 to 40 weeks postmenstrual age. For right eyes, averaged across age, the mean (SD) distance between the optic disc and temporal retinopathy was 426 (26) pixels and that between the optic disc and nasal retinopathy was 330 (26) pixels. Corresponding measurements for the left eye were 428 (30) and 332 (24) pixels. This observed asymmetry was found to be statistically significant in both left and right eyes (Mann-Whitney U test, PϽ.01). While the distance between the optic disc and retinopathy increased with age by 10 to 17 pixels per week, the extent of the asymmetry did not vary systematically with age. Conclusion: The location of retinopathy of prematurity is asymmetric along the horizontal meridian with respect to the optic disc-an observation germane to retinal vascular development, the pathogenesis of retinopathy of prematurity, and current disease classification by circular (symmetric) zones.