Eye Problems in Horses

Horses have the largest eye of any land mammal and injuries can impact training and quality of life.

Some performance organisations have set standards into the amount of vision present to protect both horse and rider welfare making eye examinations an important consideration not only when purchasing a new horse but also in preventing vision loss. A normal eye is open and clear. If you spy something wrong with your horse’s eye such as discharge, cloudiness or squinting, contact your vet for advice.

Eye Ulcers

Ulcers or scratches to the surface of the eye are common and may be caused by scratches from grass seeds or rubbing. If the ulcer is shallow, it may heal with little to no scar with minimal treatment in several days. If the ulcer is deeper, it may become inflamed and make the eye look blue. Eye ulcers can quickly become an emergency forming a melting ulcer, descemetocele, or the eye rupturing if left untreated. A melting ulcer is a serious condition and forms when bacteria or fungi attack the normal outer layer of the eye. The eye tries to fight the infection by getting rid of the diseased tissue. This self- destruction of the delicate surface of the eye leads to the eye melting like candle wax and a ‘tear drop’ forming on the surface of the eye. These ulcers can perforate (rupture) in less than 24 hours and are an emergency.

A descemetocele is a deep ulcer that is very close to rupturing. It is often not painful as there are not many nerves located deep within the eye and may be missed or seen as the eye is improving. These eye injuries require intensive medical treatment or surgical intervention to save the eye and may result in a scar on the surface or deeper within the eye. Treatment of eye ulcers can vary from topical ointment to minimise infection and provide pain relief to surgical corneal grafts. Deep ulcers like wounds on other parts of the body need to be kept free from infection and have adequate blood supply to heal. Medical support often involves topical ointments installed onto the eye every few hours through a subpalpebral lavage (SPL).

Equine Recurrent Uveitis (ERU)

ERU is an autoimmune condition that may start with an eye injury and lead to recurrent episodes of inflammation within the eye. Appaloosa and Warmblood breeds tend to be prone to the development of ERU but the underlying trigger factor is largely unknown. One or both eyes may be affected, with the eye appearing painful (closed or squinting) and a discharge may be present. On examination of the eye the eye appears blue due to inflammation and typically an ulcer is not present. The lens inside the eye may move (luxate) or form a cataract due to the repeated episodes of pain and inflammation. Medication to control uveitis are different from that of an eye ulcer and it is important to not put ointments into an eye without prior veterinarian assessment. Surgical implants have been used to minimise recurrent episodes of ERU and allow horses to compete within FEI guidelines for medication withdrawals.

Cataract

A cataract is a cloudiness of the lens affecting the amount of light that can pass through the eye, limiting vision. A horse may be born with a cataract (juvenile cataract), or a cataract may form in an adult horse due to inflammation or trauma. The size and type of cataract along with the horses intended performance determines if any treatment is required. No medication will fix a cataract or cause it to dissolve, but topical medication may be used to prevent ongoing inflammation and pain within the eye. Some cataracts can be removed, and the lens replaced similar, to what is performed in humans. Cataracts may be hereditary and should be discussed with your Equine Veterinarian if you are considering breeding.

Eye Trauma

Trauma to the eyelids or lumps near the eye may affect vision. The eye lids are important for normal vision providing protection and helping tears being spread across the surface of the eye. Eyelid lacerations may occur when horses rub their head on a bucket or fence. If seen to promptly by a veterinarian, lacerations can heal with minimal scar formation. If the eyelids are too damaged to put back together it may lead to long term damage to the eye itself due to an inability to protect the eye from dust or other objects. Small lumps near the eye may at first appear harmless. Sarcoids are a common equine tumour and can be located anywhere on the horse, initially appearing as a small, raised lump. Sarcoids around the eye (periocular) may grow so large to obscure vision and are typically harder to treat than sarcoids in other regions.

What to do if your horse has a sore eye

If you are concerned about your horse’s eye contact your Equine Veterinarian. Whilst waiting for your vet, avoid putting any creams or drops in the eye. The area around the eye can be cleaned but it is important to use non-irritant substances such as distilled water or very dilute iodine. A fly mask is also advised to minimise fly irritation until your vet can thoroughly examine the eye.