The most common tumor on the horse’s eyelid is a squamous cell carcinoma; this is the same tumor than causes cancer eye in cattle. Predisposing factors that increase the chance of this tumor occurring are similar to those in cattle, as horses lacking pigmentation around the eye or that have light-colored faces are more susceptible to these tumors due to UV light exposure. The tumor can occur on the eyelids, cornea, or third eyelid and may initially appear as a small red inflamed area that will eventually enlarge and can cover the entire eye. For this reason, it is important to monitor your horse’s eyes, especially those with white around their eyes, for small bumps on the eyelids, or tearing in one eye more than another.
Many times, horses with small squamous cell carcinomas only have inflammation of the conjunctival tissue around the globe and the horse’s response may appear similar to dust allergies. If your horse has an eye that seems to be affected, call your vet so they can take a biopsy to determine if an infection, dust or a tumor could be involved. If a squamous cell carcinoma is diagnosed, multiple treatments are available including freezing the tumor, surgical removal, hyperthermia, radiotherapy, and injecting various chemotherapeutic agents. One chemotherapeutic agent that is inexpensive and can be injected in the tumor is the chemical 5 fu. A recent report out of Oklahoma State reveals this chemical can reduce the tumor size although it is unlikely to completely cure the tumor. However, reducing the tumor may eliminate clinical signs and allow surgical removal or other treatment. If your horse has inflamed areas in or around the eyes, a tumor could be involved so call your veterinarian.