Racial differences in ocular oxidative metabolism: implications for ocular disease

Abstract

Objective: To compare the Po(2) distribution in different regions in the eyes of patients undergoing intraocular surgery.

Methods: Before initiation of intraocular cataract and/or glaucoma surgery, an optical oxygen sensor was introduced into the anterior chamber via a peripheral corneal paracentesis. The tip of the flexible fiberoptic probe was positioned by the surgeon for 3 measurements in all patients: (1) near the central corneal endothelium, (2) in the mid-anterior chamber, and (3) in the anterior chamber angle. In patients scheduled to undergo cataract extraction, Po(2) was also measured (4) at the anterior lens surface and (5) in the posterior chamber just behind the iris. Oxygen measurements at the 5 locations were compared using a 2-tailed unpaired t test and multivariate regression.

Results: The Po(2) value was significantly higher in African American patients at all 5 locations compared with Caucasian patients. Adjusting for age increased the significance of this association. Adjusting for race revealed that age was associated with increased Po(2) beneath the central cornea.

Conclusions: Racial differences in oxygen levels in the human eye reflect an important difference in oxidative metabolism in the cornea and lens and may reflect differences in systemic physiologic function. Increased oxygen or oxygen metabolites may increase oxidative stress, cell damage, intraocular pressure, and the risk of developing glaucoma. Oxygen use by the cornea decreases with age.

Figure 1

Instrument and technique of PO₂ measurement in the human eye in vivo. A, Optical oxygen sensor shown next to a standard 30-gauge tuberculin syringe needle. B, The locations in the eye where PO₂ was measured: (1) beneath the central corneal endothelium, (2) mid–anterior chamber, (3) anterior chamber angle, (4) anterior lens surface, and (5) posterior chamber.

Figure 2

Diagram of PO₂ at 5 location in the eye (see Figure 1). Measured values are shown next to those locations in the illustration. The table provides the mean (SE) and statistical significance of the differences in PO₂ between Caucasian and African American (AA) participants, unadjusted for race or age. All differences were statistically significant. AC indicates anterior chamber.

Figure 3

Scatterplots of PO₂ in Caucasian and African American (AA) patients at each of 5 intraocular locations. Solid black bars identify the mean value of the distribution. AC indicates anterior chamber.