Unilateral vision loss associated with corneal opacity and posterior lens luxation in the right eye of a Thoroughbred gelding: Case report.

A 15-year-old Thoroughbred gelding was presented for examination due to chronic corneal opacity in the right eye, which had been noted for several years. An ophthalmic evaluation revealed dense, irregular corneal opacity; an absence of the direct pupillary light reflex; and a positive dazzle reflex. Fluorescein staining was negative and cytology of a corneal conjunctival swab identified nucleated squamous epithelial cells, but no inflammatory cells. Slit-lamp examination failed to visualize intraocular structure, and the lesion was deemed to be chronic and irreversible. An obstacle-avoidance test was performed under binocular conditions and with selective monocular masking. The horse avoided obstacles with binocular vision but consistently collided with them when relying solely on its right eye. Ultrasonographic examination revealed posterior luxation of the lens into the vitreous body, accompanied by retinal thickening. These findings were consistent with chronic traumatic ocular injury, which explained the unilateral loss of vision.