Histopathological and immunohistochemical features of vitreoretinopathy in Shih Tzu dogs.

Fifty cases of Shih Tzu ocular vitreoretinopathy were selected from the database of the Comparative Ocular Pathology Laboratory of Wisconsin. Cases with severe coexisting conditions (e.g. corneal disease, uveitis or endophthalmitis) were excluded. Microscopical changes were evaluated and immunohistochemistry was used to define spindle cells, gliosis and the presence of basement membranes in the vitreous. Expression of glial fibrillary acidic protein, vimentin and smooth muscle actin was also performed. The mean age of the 50 cases was 10.1 years (range 2.5-15 years). The most characteristic microscopical abnormalities (50/50 cases) were retinal detachment and extensive retinal tear. Additionally, extracellular, eosinophilic matrix material admixed with few spindle cells, and pre-iridal fibrovascular membrane, goniodysgenesis, secondary glaucoma, hypermature and subcapsular cataract were detected. The spindle cells within the collagen matrix were strongly labelled for expression of vimentin, with weaker expression of smooth muscle actin.