50 Sudden acquired retinal degeneration
Owners will present the patient because the animal has suddenly gone blind. This may have occurred literally overnight, or may have progressed over a few days. The patient is likely to be distressed and slightly disoriented, and might be depressed or clinically unwell – with the owners reporting increased appetite and thirst. However, the patient might be totally normal except that they are bumping into things. The owners might have also noticed a change in the appearance of the eyes – shiny, glassy or perhaps just looking different. Small breed, overweight female dogs are most frequently presented. The condition has not been described in cats.
In most cases there is no previous history of ocular disease or relevant systemic disease. However, the patient might have recently gained weight and might show signs of polydipsia and polyuria. A few cases will have a history of low grade hyperadrenocorticism which is either not being treated or not controlled with treatment.
General clinical examination will reveal a lethargic, slightly overweight or even obese patient but no other specific abnormalities. The patient will be obviously totally blind – reluctant to walk, bumping into objects, head down smelling the floor and with a high stepping gait. There will be a ‘starey’ appearance to the eyes, due to the presence of dilated pupils. Menace responses will be absent. Pupils will be dilated in room light and in the dark, and will be symmetrically so. Pupillary light reflexes are usually totally absent, although slight pupil constriction might occur with a very bright light source. Dazzle reflexes will be absent.
Intraocular examination will be normal – one would expect fundus abnormalities but this is not the case – the retina and optic nerve look normal initially. However, if the patient is not presented for several weeks the early signs of retinal degeneration, with tapetal hyper-reflectivity and blood vessel attenuation, might have developed.
Possible causes of central blindness include: