Objective: To determine intraocular pressure (IOP)-related differences in the neural rim area among urban Americans without known optic nerve disease.
Design: Population-based prevalence study conducted in 16 cluster areas in East Baltimore, Md.
Participants: A population-based sample of 1521 black and 1851 white individuals aged 40 years and older without evidence of optic nerve disease.
Main outcome measure: Intraocular pressure-related differences in neural rim area, neural rim area-to-disc area ratio, and cup-to-disc ratio.
Results: We analyzed optic disc photographs using the Imagenet system (Topcon Instrument Corp of America, Paramus, NJ). After adjusting for age and disc area, white Americans had a 6% decrease in neural rim area for every 10-mm Hg increase in IOP (P = .0001). In black Americans, there was a quadratic relationship between neural rim area and IOP, with little decline with IOP up to approximately 17 mm Hg, after which neural rim area declined significantly with higher IOP (P = .001). Similarly, the neural rim area-to-disc area ratio decreased and the vertical cup-to-disc ratio increased with increasing IOP in both black and white Americans.
Conclusions: The higher the level of IOP, the smaller was the amount of neural rim tissue in the optic disc for both black and white Americans. However, the relationship between IOP and neural rim area was different in whites and blacks.