This twenty year old Hanoverian cross horse was presented with a history of gradually worsening night vision but otherwise no ophthalmioc abnormalities. Pupillary light reflex was somewhat slow and the retina appeared as shown here. What might be occuring here?
There is an unusual ‘lunar landscape’ appearance to the retina in the left eye, which may be a normal variant in an older horse, but in the right eye, shown here, there is mild tapetal hyper-reflectivity with focal areas of markedly increased reflectivity suggestive of retinal degeneration. In one study by Chadler et al (Ophthalmic lesions in 83 geriatric horses and ponies.
Vet Rec. 2003 153:319-22.) 35 of 83 older horses had senile retinal degeneration but this was generally manifest as pigmentary changes and not hyper-reflectivity with photoreceptor degeneration. The retinal appearance here ties in with the clinical signs but quite what the prognosis is for future retention or loss of vision is unclear.