Race-, Age-, Gender-, and Refractive Error—Related Differences in the Normal Optic Disc

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Abstract
Objective: To determine race-, age-, gender-, and refractive error—related differences in the size and topography of the optic disc in healthy Americans. Design: Population-based study. Setting: Eastern and southeastern health districts of Baltimore, Md. Participants: A population-based sample of 4877 noninstitutionalized black and white individuals aged 40 years or older without evidence of optic nerve disease. Main Outcome Measure: Race-, age-, gender-, and refractive error—related differences in optic disc measurements: disc area, neural rim area, cup area, cup-to-disc ratio, and neural rim area—to—disc area ratio. Results: We analyzed simultaneous stereoscopic optic disc photographs from 3387 (1534 black and 1853 white) of the 4877 healthy individuals using an image analyzer (Topcon Image Analyzer, Topcon Instrument Corporation, Paramus, NJ). A total of 1490 individuals were excluded owing to the absence of good-quality images from either eye. The image analyzer defined the cup margin 150 μm below the surface of the disc margin. On average, blacks had significantly larger disc areas (blacks, 2.94 mm2; whites, 2.63 mm2), larger cup areas (blacks, 1.04 mm2; whites, 0.71 mm2), larger cup-to-disc ratios (blacks, 0.56; whites, 0.49), similar neural rim areas (blacks, 1.90 mm2; whites, 1.92 mm2), and smaller neural rim area-to—disc area ratios (blacks, 0.66; whites, 0.74) compared with whites. There were no age-related differences in any of the disc measurements. Male subjects had 2% to 3% larger optic discs compared with female subjects. No association between refractive error and any of the optic disc mesurements studied was detected. Conclusions: Racial differences in the normal optic disc are present among urban Americans, and these differences must be considered in evaluation of the optic disc for glaucoma and other optic neuropathies. Among the individuals in our study, all of whom were 40 years of age or older, no progressive age-related decline in neural rim area was detectable. Neither gender nor refractive error were associated with any significant differences in the size and topography of the normal optic disc.

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