Diagnostic Exercise: Retinal Lesions in a Mouse

Inherited retinal degeneration was identified in a Swiss-derived mouse strain. The histological lesions are described and the pathogenesis of the condition is discussed. A group of 16-22 g, female, ICR Swiss mice was obtained from a commercial supplier for a toxinology experiment. One mouse of this group was submitted for routine necropsy and histologic examination as part of the quality control program at the research institute. No abnormalities were noted clinically. Gross lesions were not seen at necropsy. Histologic lesions were limited to the eyes. Changes were present and similar in the retina of both eyes. The outer layers of the retina were characterized by attenuation and loss of the outer plexiform, outer nuclear, and photoreceptor layers. The outer nuclear layer was reduced to a discontinuous single row of nuclei. The photoreceptor layer was represented by an eosinophilic, granular coagulum or was absent altogether. An outer limiting membrane could not be defined by the use of special stains. The nonpigmented retinal pigment epithelium was unaffected.