The purpose of the study was to investigate whether removal of the lens would change the physiology of oxygen supply to the anterior segment of the eye. Oxygen partial pressure in the anterior chamber was measured using oxygen-sensitive electrodes during cataract surgery or removal of after-cataracts in aphacic and pseudophacic eyes. We found significantly reduced oxygen tension in the anterior chamber of aphacic or pseudophacic eyes compared to cataractous eyes. These results could be explained either by a reduced barrier between aqueous humor and vitreous or by atrophic changes of the iris vasculature after cataract surgery. These changes in oxygen supply to the anterior chamber after cataract surgery could be clinically relevant in the eyes with ischemic diseases.