In the early stages of glaucoma, it can be difficult to make a diagnosis. The presenting sign is usually an eye with some mild edema (fluid within the cornea, which shows up as a white or blue haze on the outside of the eye) and potentially mild pain. There are several other diseases that cause these same signs which are much more common than glaucoma. The only way to truly diagnose glaucoma is by measuring the intra-ocular pressure. Given the rarity of the condition, most equine vets do not carry the equipment required to do this. So for most field vets, glaucoma becomes a diagnosis of exclusion. We should say here that glaucoma is extremely difficult to control in horses and that the disease usually progresses even in the face of early aggressive treatment.
Glaucoma is not frequently diagnosed in horses, but we still must consider it in cases of a chronically inflamed eye which is not responding to normal treatments. Unfortunately, the disease process is not well understood in horses and most information is extrapolated from other species. As more becomes known, and more research is done, we hope that we may be able to develop better ways to combat this vision threatening disorder.