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

Unilateral vision loss in a Thoroughbred horse was linked to chronic corneal opacity and lens displacement in one eye, resulting from past traumatic injury.

Case Presentation

• A 15-year-old Thoroughbred gelding exhibited persistent corneal opacity in the right eye, which had been present for several years.
• Owners reported no recent changes, indicating a long-standing, chronic condition.

Clinical Examination Findings

• Ophthalmic evaluation showed:
  • Dense, irregular corneal opacity obscuring normal eye structures.
  • Absence of direct pupillary light reflex (no pupil constriction when light shined in the right eye).
  • Presence of a positive dazzle reflex (involuntary eyelid blink in response to bright light).
• Fluorescein staining test was negative, indicating no active corneal ulceration or surface damage.
• Cytology from a corneal conjunctival swab revealed nucleated squamous epithelial cells without signs of inflammation, suggesting no ongoing infection or inflammation.
• Slit-lamp examination could not visualize intraocular structures due to opacity, signifying a chronic irreversible lesion.

Functional Vision Testing

• An obstacle-avoidance test assessed the horse’s visual capability under two conditions:
  • Binocular vision (both eyes open) – the horse successfully avoided obstacles.
  • Monocular vision with right eye masked – the horse consistently collided with obstacles, confirming impaired vision in the right eye.

Ultrasonographic Findings and Diagnosis

• Ultrasound of the right eye demonstrated:
  • Posterior luxation of the lens – the lens was displaced backward into the vitreous body (the gel-like substance inside the eye).
  • Retinal thickening – indicative of retinal changes possibly secondary to trauma or chronic disease.
• These findings are consistent with chronic traumatic ocular injury, which likely caused the permanent vision loss in the affected eye.

Summary and Clinical Significance

• The case highlights the impact of long-term eye trauma in horses, resulting in corneal opacification and lens luxation leading to unilateral blindness.
• Diagnostic tools included clinical ophthalmic tests, cytology, functional vision testing, and ultrasonography.
• Understanding such chronic ocular conditions is important for managing equine patients with unilateral vision loss and informing prognosis and treatment options.