Crescentic cataracts in Alderley Park rats.

The ophthalmoscopic appearances and the clinical evolution of a previously poorly documented form of crescentic cataract was studied in over 2,000 untreated Alderley Park rats between 4 and 110 weeks of age. In addition, 401 ex-breeder females, 54 gonadectomized males, and 56 gonadectomized females of the same strain were studied. The light microscopic features of the lenticular changes were also examined in detail. The cataracts, crescentic in shape and originating dorsally at the lens equator, were mostly unilateral. They appeared from about 30 weeks of age and affected 4% of intact males and 14% of intact females by about 2 years of age. Fewer cataracts were found in ex-breeder females, and none were found in male or female gonadectomized rats up to 2 years of age. The cataracts developed rapidly and became fully formed in 3 months. Subsequently, most cataracts scarcely progressed. Only a few extended to involve the entire lens. Some appeared to regress completely. Histologically, affected lens fibers showed swelling, globular disintegration, and liquefaction, most marked in the cortex medial to the lens bow area and extending along the direction of the lens fibers in an anterior and posterior direction but only occasionally reaching the lens capsule. The cause of these age-related lenticular changes in the Alderley Park rat is uncertain, but these changes are important during the conduct of long-term studies with this strain because their incidence can be modulated by agents that alter sex hormone status.