Tumors of the eye itself are very rare in horses, but tumors of the structures around the eye are surprisingly common. | Photo: Courtesy Dr. Anna Hollis/Equine Disease Quarterly

Neoplasia is abnormal tissue growth which, if it forms a mass, is commonly known as a tumor. Neoplasia can be benign (these tend to be less destructive) or malignant (these tend to be invasive and can spread to other tissues, a process known as metastasis).

Tumors of the eye itself are very rare in horses, but tumors of the structures around the eye are surprisingly common. The most commonly diagnosed types of neoplasia in this area are sarcoids, melanomas, and squamous cell carcinomas (SCCs). Others such as lymphoma and mast cell tumors can also be found. Most tumors around the equine eye do not metastasize, but they can be locally aggressive and have serious effects on the horse’s welfare and use. Early treatment is therefore strongly recommended.

Sarcoids

Believed to be the most common equine skin tumor, sarcoids can take various forms. Those that develop around the eye are frequently aggressive in nature, invading into the eyelid musculature, especially those located on the upper eyelid. Horses will usually have additional sarcoids in other locations, so a thorough examination of the horse is recommended to identify any other lesions that need to be treated