Phase separation and lens cell age.

Using laser light scattering spectroscopy, we are studying age-related changes in the microstructure of lens cytoplasm. We have established in animal models that one of the earliest identifiable stages in cataract development is the presence of a phase transition in the lens cytoplasm. As a result of the phase transition, the cytoplasm separates into microvolumes that differ in their protein concentration. These microvolumes scatter light and cause the lens to become opaque. This phase separation occurs in normal lens cells at a characteristic temperature, Tcat, which varies across the lens with the cell age. As the animal becomes older, the Tcat for the nuclear cells decreases to a value well below body temperature. In X-irradiated eyes, however, Tcat increases with animal age until the phase separation occurs at or near body temperature. At this point, a well-developed nuclear cataract appears. We are now attempting to understand the biochemical basis for the differences between Tcat of normal and Tcat of X-irradiated lens cells during the aging process.