Unsteady aspects of corneal thickness control

Abstract

Unsteady-state calculations of rabbit corneal thickness dynamics show that the stromal hydration changes slowly in response to the normal sleep/wake variations in tear osmotic pressure. Consequently, the corneal thickness never varies very far from thatthickness which it would attain were the tear tonicity held constant at a value between those characteristic of the open eye and the closed eye. This intermediate “time-average” tonicity exceeds that of the stromal fluid, and it is shown that, in the normal eye, the consequent osmotic driving force across the epithelium, averaged over time, can generate sufficient flow out across this cell layer to balance completely stromal imbibition across the endothelium. The implications of this result as regards the role of active deturgescent transport are discussed, and some directions for synthesizing current hydration control concepts are indicated.