Mechanisms initiating cataract formation. Proctor Lecture.

Osmotic swelling is a common feature of many cataracts. Sugar cataracts and hereditary mouse cataracts are two types in which osmotic changes play a prominent role. In sugar cataracts, the initial swelling brought about by polyol accumuation leads to an imbalance in the pump-leak equilibrium. The pump mechanism becomes unable to keep pace with the leaky membranes. The marked increases in Na and Cl eventually results in Donnan swelling. In the hereditary mouse cataract, the imbalance of the pump-leak system appears to be initiated by a deficiency of Na-K ATPase, a component of the cation pump mechanism. The inefficiency in the pump mechanism results in Na retention and osmotic swelling.