The superior cornea is continuously covered by the upper eyelid. Corneal oxygen uptake profile studies have presented inconclusive evidence on the question of whether the superior cornea adapts to this chronic hypoxia. We measured thickness profiles in the vertical corneal meridian on one eye of 19 male subjects between ages 24 and 41 y who were adapted to daily hydrogel lens wear. At an 8 mm chord diameter, the superior cornea was approximately 30 um thicker than the inferior cornea. This difference was highly significant (p .05). To examine the role of hypoxia in these differences, we measured corneal thickness profiles on 16 of the subjects following 2, 4 and 6 h of closed eye wear of a uniform thickness hydrogel lens (Dk/L = 17). Under these conditions of uniform oxygen deprivation, corneal swelling stabilized at 4 h, with the superior and inferior thickness differences consistently retained. This suggests that the greater thickness of the superior cornea is more likely to be anatomical than hypoxic in origin. Study funded by Bausch & Lomb.