Objective: The case histories described each presented with a visual deficit, varying from permanent total blindness with ophthalmoscopic evidence of optic atrophy to variable and transient visual disturbances, including occasional blindness, but with absence of ophthalmoscopic or any other ocular abnormality.
Animals studied: Three horses of widely different age and type, but all with an original history of upper respiratory tract infection.
Procedure: All three cases were examined by a specialist veterinary ophthalmologist. In addition, magnetic resonance imaging (MRI) and, where possible, postmortem and histopathological examinations were performed.
Results: The common factor to all three cases proved to be infection of the spheno-palatine sinuses with subsequent distension and compression of adjacent optic nerve(s) and optic chiasm.
Conclusions: Specialist veterinary ophthalmological examination proved of extremely limited value. The importance of MRI (and CT) scans for accurate diagnosis, and therefore possible successful treatment, is emphasized. Our cases were compared with similar cases in man, where visual disturbances due to spheno-palatine sinus involvement are recognized, but rare, in similar situation.