Intraocular melanoma in a horse.

This article presents the findings of a study into a rare case of intraocular melanoma in a seven-year-old gray gelding Quarterhorse that suffered from sudden unilateral blindness.

Description of the Case

• The clinical symptoms began with the unexpected onset of blindness in one eye of the horse.
• Upon conducting an ophthalmoscopic examination, a pigmented mass was detected. This mass originated from the nasal ciliary body of the right eye, subsequently wrapping itself around the posterior surface of the lens. Moreover, pigmented particles were found present in the vitreous, the clear gel that fills the space between the lens and the retina.

Post-Examination Observations

• After enucleation, the removal of the eye leaving the eye muscles and remaining orbital contents intact, a further examination took place. This investigation revealed the presence of a defined and symmetrically ovoid mass within the outer layer of the eyeball.
• The mass was black and dense, with a sessile attachment to the nasal ciliary region and had spread to the posterior lens capsule and vitreous. Additionally, it extended along the vitreal face of the detached retina towards the optic papilla, the area where the optic nerve enters the eyeball.

Cellular Composition of the Mass

• The mass was comprised of heavily pigmented, rounded, and multi-sided cells. These cells had infiltrated the vitreous and the inner limiting membrane of the peripapillary retina (the area surrounding the optic disk) and the optic papilla.

Final Diagnosis

• Based on the observed characteristics and comparisons to existing medical knowledge, the mass was identified as a primary, malignant, intraocular melanoma that had likely resulted from a large uveal nevus (a harmless, pigmented growth or mole usually found on the white part of the eye).