Distribution of Intraocular Pressure

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Abstract
Objective: To provide data on the distribution of intraocular pressure (IOP) in a predominantly black population, which has a high prevalence of open-angle glaucoma. Design: Population-based prevalence study. Setting and Participants: Participants (N=4601) (age range, 40-84 years) who had undergone applanation tonometry measurements in the Barbados Eye Study. Self-reported race was 93% black, 4% mixed (black and white), and 3% white or other. Data Collection: A standardized protocol included applanation tonometry and other ocular measurements, fundus photography, demographic data, and an interview. Main Outcome Measures: The average of 3 IOP measurements at the Barbados Eye Study visit was used to compare IOP by self-reported race. Descriptive data on IOP by age, sex, glaucoma status, and cup-disc ratio were examined in the black population. Results: The IOP was highest in the population of African origin. The mean (±SD) IOP values for black, mixed, and white participants were 18.7±5.2, 18.2±3.8, and 16.5±3.0 mm Hg, respectively. An IOP greater than 21 mm Hg was present in 18.4%, 13.6%, and 4.6% of the black, mixed, and white participants, respectively. In analyses that were adjusted for age, sex, and glaucoma status, such values were 5 times as likely in black than white participants and 3.5 times as likely in mixed race participants (P<.01). Among the black participants, the mean IOP increased approximately 1 mm Hg for every increase in 10 years of age. After excluding persons with any type of glaucoma, suspected glaucoma, or a history of glaucoma treatment, women had significantly (P<.01) higher IOP values; however, no significant IOP trends by sex were evident in the group with glaucoma. The IOP was also positively associated (P<.05) with vertical cup-disc ratios. After 2 visits, the IOP remained 21 mm Hg or less in 21% of the persons with glaucoma vs 64% of those without glaucoma. Conclusions: In the black participants, the IOP was higher than in the white participants. The IOP was also associated with age and cup-disc ratios. The results showed that open-angle glaucoma and a high IOP alone have a different distribution by sex; although open-angle glaucoma was more frequent in men, ocular hypertension was more frequent in women. These data have implications for the detection and causation of open-angle glaucoma in this high-risk population.