Iris vasculopathy is a well-recognized clinical feature in pseudoexfoliation syndrome (PES). In the present study we examined the morphology of the iris vasculature in PES using electron microscopy and we tested whether these iris vascular changes were correlated with an impaired oxygen supply to the anterior chamber. In the affected vessels we found a gradual degeneration of vascular cells, progressing from adventitial to endothelial cells, associated with the production of excess extracellular material, including pseudoexfoliative fibers. Oxygen partial pressure (pO2) was measured in the anterior chamber during cataract surgery using a polarographic oxygen electrode in eyes with and without PES. The pO2 value measured in the anterior chamber of 10 eyes without PES was 45 +/- 11 mmHg (mean +/- SD) in the chamber angle, 33 +/- 12 mmHg in front of the pupillary margin, and 13 +/- 8 mmHg in the center of the pupil. This spatial distribution of pO2 indicates that aqueous humor oxygenation occurs along the anterior iris surface. The mean pO2 values obtained in 8 patients with PES were 19 +/- 6 mmHg in the chamber angle, 16 +/- 4 mmHg in front of the pupillary margin, and 8 +/- 3 mmHg in the center of the pupil. We conclude that anterior-chamber hypoxia due to iris vasculopathy may represent a complication of PES that could play a role in the pathogenesis of PES-associated alterations in the anterior segment of the eye.