Retinopathy of Great Pyrenees dogs: fluorescein angiography, light microscopy and transmitting and scanning electron microscopy

Objective Investigation of the pathogenesis of Great Pyrenees retinopathy. Animals One male and two female puppies of parents who were affected with Great Pyrenees retinopathy and one 4‐year‐old affected adult male Great Pyrenees dog. Procedure The puppies were examined daily from 7 weeks of age by indirect ophthalmoscopy and their fundi were photographed until the lesions were static. Fluorescein angiography was completed at 7 weeks of age, within 24 h of detection of ophthalmoscopic lesions, and then weekly. The eyes of a 4‐year‐old and two 20‐week‐old puppies were examined with light microscopy, and transmitting and scanning electron microscopy. Results Blocked choroidal fluorescence was detected at 7 weeks of age. The blocked fluorescence enlarged, when the characteristic serous retinal detachments developed at 11 weeks of age. The detachments enlarged in size and number until the puppies were approximately 20 weeks old. Fluorescein pooling confirmed the presence of transient retinal pigment epithelial detachments. Leakage of dye into serous retinal detachments was not detected in this study. Light microscopy and transmitting and scanning electron microscopy confirmed the presence of multifocal serous retinal detachments with focal retinal degeneration that extended to the inner nuclear layer in a 4‐year‐old dog. The retinal detachments were accompanied by hypertrophy, hyperplasia, increased pigmentation, and vacuolation of the retinal pigment epithelium. Conclusions and clinical relevance Great Pyrenees retinopathy is manifested by multifocal serous retinal and retinal pigment epithelial detachments. These detachments are similar to those noted with central serous retinopathy of humans. The sudden development of multifocal retinal and retinal pigment epithelial detachments, and the serous nature of these detachments, supports a theory that they develop secondary to focal secretion and absorption defects in retinal pigment epithelial cells. Given the age of the puppies when the blocked choroidal fluorescence was noted and maturation of the dog retina at 8 weeks postpartum, this retinopathy is considered to be a retinal pigment epithelial dysplasia. This unique inherited retinopathy offers an opportunity to study retinal pigment epithelial secretion.