Examination of the eye in experiments designed to test the toxicity of drugs or chemicals is of considerable importance and the investigator must have a clear idea of the spontaneous eye changes he can expect in the test species. We have attempted to review the literature relating to commonly used laboratory animals--the rat, mouse, and dog as well as the hamster--but as there is still only a handful of workers that publish their findings, the literature is not fully comprehensive. Our own unpublished data have been used to try and provide a more complete account. There is, therefore, a considerable need for further work in this area and, in the future, newer techniques such as electron microscopy and histochemistry can help us in the understanding of the pathogenesis of age-related changes in laboratory animals.

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Ocular abnormalities, consisting of retinal atrophy, optic neuriris, cataract, and microphthalmia with retinal dysplasia occurred in calves born to Cows artificially infected with BVD-MD virus. Retinal lesions were also seen in the calves from a naturally-infected herd. The degree of retinal atrophy varied from back of formation of normal layers to focal loss of the rod and cone layer with pigmentary migration. Cataracts were primarily cortical. There were acute and chronic optic neuritis.