Conditions or ailments that are the cause of a problem that you see - your observation.

Your vet may diagnose

Squamous Cell Carcinoma of Eye, Eyelid or Third Eyelid


Squamous cell carcinoma is the most common cancer of the equine eye, and has a higher incidence at high elevations where the UV light index is high.

It often appears as red or pink looking growth or change in appearance of the eyelid, the third eyelid (at the inside corner of the eye), or on the eye itself on the limbus (where the cornea and conjunctiva that cover the white of the eye meet).

Appaloosa, pinto and paint breeds tend to develop SCC due to the lack of pigment around their eyes. SCC is also more prevalent in some draft breeds including Haflingers, and may have a genetic component.

If this cancer is identified early, local chemotherapy, cryotherapy, and surgery may eliminate it and save the eye. Surgical removal of the third eyelid can be curative and is a relatively simple procedure if performed early in the course of diseae.

However, once SCC is advanced, eye removal (enucleation) becomes the treatment of choice. Without appropriate treatment, spread to other local structures and distant organs is possible.

my vet's role


Prognosis depends on whether or not the tumor has invaded the tissues behind the eyeball, and how aggressive the particular tumor is, which is often gauged by how rapidly it is changing and growing.

Prognosis is fair to good with early treatment, but poor if allowed adequate time to spread.

Prognosis is comparatively more guarded if a significant portion of the eyelid tissue is involved, and eyelid reconstruction is necessary.

my role


I might observe

You might make these observations when a horse has this condition.

Very Common
Less Common
more observations

Questions To Ask Your Vet:
  • What are the chances of recurrence after treatment?
  • What is the likelihood that this will occur in the other eye?
  • Is removal of the third eyelid the best choice, any complications associated with this procedure?

Monitor your horse's eyes carefully, paying special attention to the margin of the third eyelid.

Be especially vigilant with older horses, horses that live at high altitudes, and Appaloosas, American Paint and other horses that have poorly pigmented areas around their eyes. Use good quality fly masks with UV protection and reduce turnout in direct sunlight.

further reading & resources

Related References:

Higgins AJ, Snyder JR eds. The Equine Manual. 2nd Ed. Edinburgh: Elsevier Saunders 2006.

Author: Doug Thal DVM Dipl. ABVP