Equine Eye Disease at a Glance
Horses rely heavily on vision β eye problems are emergencies that require prompt veterinary attention.
Equine Eye Disease Frequency
Eye Conditions & Treatment Guide
| Condition | Signs | Urgency | Treatment |
|---|---|---|---|
| ERU (Uveitis) | Squinting, tearing, cloudiness | Emergency: 24-48 hrs | Atropine, steroids, NSAIDs |
| Corneal ulcer | Pain, holding eye closed, discharge | Emergency: same day | Antibiotic drops, stain check |
| Cataract | White/opaque lens no pain | Routine (non-emergency) | Surgery if vision impaired |
| Glaucoma | Cloudy, enlarged globe | Emergency: immediate | Pressure-lowering meds |
| SCC (cancer) | Pink/red mass on third eyelid | Urgent: 1-2 weeks | Surgical excision, cryotherapy |
Eye Emergency Timeline
Eye Emergency Response
| Call your vet immediately if a horse is squinting with tearing | |
| Keep the horse in a dark stall to reduce light sensitivity | |
| Apply fly mask to protect the eye from debris and light | |
| Note whether the pupil is constricted or irregular | |
| Flush the eye with sterile saline if debris is visible | |
| Apply any ointment without veterinary diagnosis β some worsen ulcers | |
| Assume squinting is 'just an irritation' β it's almost always painful | |
| Rub the eye β this can rupture a weakened cornea | |
| Delay treatment β uveitis can cause permanent damage in 24-48 hours |
Equine Recurrent Uveitis (ERU) β also called 'moon blindness' β is the leading cause of blindness in horses worldwide. Appaloosa and draft breeds are genetically predisposed.
A horse holding an eye partially or fully closed ALWAYS indicates pain. Never dismiss this as 'just a little irritation' β it warrants an immediate vet call.
Horses have the largest eyes of any land mammal and are disproportionately prone to serious ocular disease. Equine Recurrent Uveitis (ERU) -- the leading cause of blindness in horses worldwide -- affects an estimated 8--25% of horses in some populations. Eye problems in horses are emergencies: delays of even 12--24 hours can convert a treatable condition into permanent vision loss. Any horse showing a closed eye, excessive tearing, cloudiness, or visible injury requires same-day veterinary examination.
| Condition | Key Signs | Urgency |
|---|---|---|
| Equine Recurrent Uveitis | Cloudy eye, photophobia, pain | Same-day vet at first flare |
| Corneal Ulcer | Tearing, blepharospasm, fluorescein uptake | Emergency β hourly topicals required |
| Simple Conjunctivitis | Mild discharge, redness β no cloudiness | Urgent; not an emergency |
Anatomy and Why Horses Are Vulnerable
A horse's eye is positioned laterally on the skull, giving nearly 350-degree monocular visual field but a blind spot directly in front of the nose and behind the hindquarters. The eye itself is large (35--40 mm diameter vs. 24 mm in humans), with a horizontally elongated pupil that dilates slowly. This slow dilation means horses are more vulnerable to retinal damage in bright light transitions. The large eye also means any corneal injury covers a larger tissue area, increasing risk of rapid progression.
Equine Recurrent Uveitis (Moon Blindness)
ERU is a periodic, immune-mediated inflammation of the uveal tract (iris, ciliary body, choroid). Attacks cause painful, red, light-sensitive eyes with a cloudy anterior chamber. Without treatment, repeated attacks lead to cataracts, retinal detachment, and blindness. Appaloosas are 8x more likely than other breeds to develop ERU due to a genetic predisposition. Leptospirosis infection is a documented trigger. Treatment during flares: topical atropine (1% solution, 2--4 times daily to dilate pupil and reduce synechiae), topical corticosteroids or NSAIDs, and systemic flunixin meglumine for pain. Long-term management: cyclosporine intravitreal implants show 80--90% success in reducing flare frequency in surgical candidates. Call your vet at the first sign of squinting or tearing.
Corneal Ulcers
The most common ocular emergency in horses. Caused by trauma, foreign bodies, bacterial or fungal infection. Fungal keratitis is particularly severe and common in warm, humid climates -- Aspergillus and Fusarium spp. penetrate corneal stroma rapidly. Treatment: hourly topical antifungals (natamycin or voriconazole) for fungal cases; broad-spectrum antibiotics for bacterial ulcers. Subpalpebral lavage systems allow frequent medication delivery without repeated eye manipulation. Never use topical corticosteroids on an ulcerated cornea -- they dramatically worsen fungal infections and can cause globe rupture.
Periodic Ophthalmia vs. Acute Conjunctivitis
Simple conjunctivitis (discharge, mild redness without corneal cloudiness) responds to topical antibiotics and fly control. It does not cause the severe pain response of uveitis or ulcers. If a horse shows photophobia (keeping the eye shut in normal light), blepharospasm (eyelid spasm), or excessive lacrimation, assume a serious condition until ruled out by exam. Fluorescein dye staining and slit lamp examination differentiate diagnoses.
Routine Eye Care
Fly masks with UV protection reduce debris, insect irritation, and UV exposure (a risk factor for squamous cell carcinoma of the third eyelid in horses with light-colored periorbital skin). Clean any ocular discharge daily with saline-moistened gauze. Annual equine wellness exams should include basic ophthalmic assessment.
Sources: Merck Veterinary Manual -- equine uveitis; ACVO (American College of Veterinary Ophthalmologists) ERU clinical guidelines; peer-reviewed research on Appaloosa ERU genetics (Equine Veterinary Journal 2019); AAEP equine eye disease proceedings.