Aging and the optical quality of the rat crystalline lens.

Split laser beams of varying separation were directed through the crystalline lenses of rats of young, old, and intermediate age. The variation in back vertex distance was determined from photographs of the focal effects of each lens. The results indicate that negative spherical aberration of the rat lens increases with age. In addition, local reversals in the slopes of the negative spherical aberration curves are larger and more frequent in the older lenses. The increase in negative spherical aberration is likely due to tighter packing of central lens fibers and a consequent increase in central refractive index although change in lens shape may contribute as well.