Abstract
Background: to describe the clinical, diagnostic imaging and histopathological findings of two visually impaired closely related horses and to identify a possible cause.
Case description: two Warmblood horses, with a common dam and sire, were presented to our ophthalmology department for investigation of impaired vision. Information collected included physical and ophthalmic examination findings, results of ocular ultrasound, electroretinogram, magnetic resonance, histopathology and genetic testing for multiple congenital ocular anomalies (MCOA). Ophthalmologic examination of the two horses revealed a complete retinal detachment in the left eye and vitreous synaeresis in both eyes of both horses. Ocular ultrasound and magnetic resonance imaging confirmed those findings. Electroretinograms showed a normal response in both right eyes but a total loss of the retinal response in their left eyes. Histopathologic examination revealed multifocal retinal dysplasia in both left eyes. The most affected horse tested negative for the PMEL17 gene, responsible for MCOA.
Conclusion: in these two horses, retinal detachment has likely been caused by the congenital posterior segment abnormalities of the vitreous and the retina. A vitreoretinopathy is highly suspected and is possibly hereditary in these closely related siblings.

Key words: Horse, Retinal detachment, Retinal dysplasia, Synaeresis, Vitreoretinopathy