Persistent hyaloid vascular system in age-related cataract in a SAM strain of mouse.

The cataractogenesis of age-related cataract in a strain of Senescence-Accelerated Mouse; SAM-P/9 was investigated. In the mature cataract, funnel-shaped tissue of the persistent hyaloid vascular system extended from the retinal papilla and covered the extremely protruding posterior pole of the cataractous lens, as seen using a stereomicroscope. Longitudinal examination of the eyes with transparent lenses using an ophthalmoscope revealed that the hyaloid vascular system persisted in about 90% of the 5-week-old mice, at least unilaterally. The eyes with transparent lenses in some old mice retained this tissue and a retrospective study revealed that cataract never occurred in eyes without this tissue. Microphthalmos was not observed. Histologically, in the eyes with transparent lenses, the posterior lens capsule covered with a hyaloid vascular system became very thin but only a few lens fibre cells just inside the capsule had swelled. In the lens of the mature cataract or even with initial changes, the lens capsules ruptured. Electron microscopic examination showed that the persistent hyaloid vascular system was tissue consisting of capillary and mesenchymal cells. These observations suggest that the persistent hyaloid vascular system is a necessary but not sole factor for age-related cataract formation in SAM-P/9, and that other age-related factors probably have a role.