Oxygen in the anterior chamber of the human eye

Oxygen partial pressure (pO2) was measured in the anterior chamber of the human eye during routine cataract surgery using a polarographic oxygen electrode. We found a reproducible spatial distribution of oxygen in the aqueous humor. The pO2 (n = 8) was 44.9 +/- 9.1 mmHg in the chamber angle, 35.0 +/- 10.9 mmHg above the pupillary margin, and 13.5 +/- 8.0 mmHg in front of the center of the pupil. Pretreatment of the eye with the alpha-adrenergic agonist phenylephrine (5%) resulted in a marked reduction in pO2 to 19.8 +/- 5.8 mmHg in the chamber angle, 13.4 +/- 4.7 mmHg above the pupillary margin, and 7.4 +/- 3.3 mmHg in front of the center of the pupil (n = 8). The pO2 in the anterior lens was very low (2.5 +/- 0.6 mmHg, n = 7). We conclude that oxygen is supplied at the anterior iris surface to the aqueous humor. The lens is an extremely low oxygen compartment. Topical phenylephrine causes anterior-segment hypoxia, probably by the constriction of iris vessels.