Extraocular lymphoma in the horse

To describe the clinical findings and prognosis for extraocular lymphoma in the horse.

Retrospective medical records study of horses diagnosed with third eyelid, corneoscleral, conjunctival, and/or eyelid lymphoma from multiple academic and private veterinary institutions. Data collected from the medical records included signalment, clinical descriptions of the extraocular lesions, treatment, and treatment outcomes. Nonparametric statistical analysis was performed with Fischer's exact tests.

Extraocular lymphoma involving the eyelid, third eyelid, cornea, sclera, and/or conjunctiva was diagnosed in 26 horses. Differences in signalment, unilateral vs. bilateral extraocular involvement, and single vs. multiple extraocular lesion locations held no significance in terms of outcome.

Horses with lesions localized to the eyelid or other nonextraocular cutaneous locations had a significantly higher chance of negative outcome when compared to the horses with no eyelid or cutaneous involvement (P = 0.019). Lesions to the third eyelid, corneosclera, and conjunctiva were either nodular or diffuse in nature. Nodular lesions when compared to diffuse lesions were associated with a higher chance of a positive outcome (P = 0.007). Surgical resection of the extraocular lesions as part of the treatment produced a statistically higher chance of a positive outcome when compared to horses where resection was not performed (P = 0.03).

The prognosis for clinical remission in horses with extraocular lymphoma is generally fair to good, as long as the affected tissues are completely excised, and there is no eyelid or cutaneous involvement. Horses diagnosed with the nodular form of extraocular lymphoma seem to have the best prognosis with complete excision.