Your horse’s eyes are beautiful and expressive, but many conditions can affect equine eyes, potentially threatening their vision. Our team at Leatherstocking Veterinary Hospital wants to provide information about some common eye conditions diagnosed in horses, to ensure you know when your horse needs veterinary attention.

Corneal ulcers in horses

A corneal ulcer is any disruption in the corneal integrity, and, regardless whether these lesions are shallow or deep, a corneal ulcer is always a veterinary emergency. Pathogens, such as bacteria and fungi, can invade the smallest defect in the cornea, resulting in serious complications. In addition, inflammation develops inside the horse’s eye when a corneal ulcer is present, and this inflammation can lead to long-term consequences if left untreated. Causes of corneal ulcers include trauma, foreign objects, eyelid abnormalities, and corneal tissue infections. The earliest signs that your horse may have a corneal ulcer include tearing, squinting, and a sensitivity to light, and you should contact Leatherstocking Veterinary Services if your horse is exhibiting any of these signs, so we can evaluate their eye. As the ulcer progresses, your horse’s eyelids may swell shut, and the cornea may become cloudy or blue. 

Sedation is often required to appropriately examine your horse’s eye, since the condition is so painful. A bright light source will be used to evaluate your horse’s cornea, and an ophthalmoscope will be used to examine the back of your horse’s eye, looking for evidence of inflammation. Your horse’s eye will be stained using fluorescein stain that adheres to the deeper layers of the cornea, but not the outermost layer. Any defect will turn a bright green color after staining. In some cases, samples may be taken from your horse’s eye to perform cytology or culture. A treatment protocol will be determined based on the type and severity of your horse’s corneal ulcer. 

• Simple superficial ulcers — If your horse’s ulcer is superficial and shows no infection signs, you will likely be asked to administer an antibiotic ointment to your horse’s eye several times a day. Your horse will also need a nonsteroidal anti-inflammatory drug (NSAID) to improve their comfort level, and decrease inflammation inside the eye.
• Indolent ulcers — These ulcers typically affect older horses and occur when the ulcer fails to heal appropriately, because the new cells don’t adhere to the underlying corneal tissue. The ulcer typically needs debriding to get healthy tissue to grow.
• Equine ulcerative keratomycosis — This occurs when the ulcer is infected by fungi. Fungal infections can be difficult to manage, and can quickly progress. Your horse will likely need antibiotic and antifungal drops administered frequently throughout the day and night, and NSAIDs to help control their pain and inflammation.
• Melting ulcers — Certain bacteria can cause your horse’s white blood cells to release enzymes that digest the corneal stroma. These ulcers require around-the-clock medication every two hours, and in some cases, surgery is necessary to remove the infected tissue.
• Descemetocele — These ulcers are extremely deep, involving all but the deepest corneal layer, and need immediate veterinary intervention to help prevent corneal rupture. These lesions often require surgery, such as a corneal graft or a conjunctival flap, to help support the damaged tissue.

Uveitis in horses

Uveitis refers to inflammation inside the eye, and any time your horse’s eye is injured, uveitis can occur. Horses are also susceptible to equine recurrent uveitis (ERU), a condition that is likely a complex autoimmune disease influenced by genetic and environmental factors. Appaloosas are eight times more likely to develop ERU than other breeds, and more than half of affected horses will eventually lose their vision. Other breeds at higher risk include quarter horses, thoroughbreds, warmbloods, and paint horses. Infectious organisms, such as Leptospira spp., have also been associated with ERU. Signs include recurrent squinting, tearing, and light sensitivity episodes. The affected eye may turn colors, and become red, cloudy, or blue. ERU treatment options include:

• Medical treatment — Topical NSAIDs and corticosteroids can be used to reduce inflammation. Systemic NSAIDs are also necessary to alleviate pain and further decrease inflammation inside the eye.
• Suprachoroidal cyclosporine implant — A sustained-release cyclosporine implant can be surgically placed, providing relief for some horses for up to three years.
• Core vitrectomy — This surgical procedure removes the inflamed vitreous. This approach has been shown to successfully control inflammation and reduce recurrence.
• Enucleation — Removal of the affected eye is necessary, if the pain can’t be controlled.

Cataracts in horses

Cataracts occur when proteins in the horse’s lens break down, causing the lens to become cloudy. Some breeds, including thoroughbreds, Morgans, and Belgian horses, are at higher risk for developing congenital cataracts. Other causes include senile cataracts, thought to be caused by repeated boughts of uveitis, nutritional deficiencies, and trauma. Since the lens is deep inside the eye, you may not realize your horse has a cataract. Signs include pupil cloudiness, unexplained shying, and jumpiness.

Cataracts are diagnosed through visualization on an ophthalmic examination. Incipient cataracts involve only a small lens portion, and usually do not affect your horse’s vision. Immature cataracts progress with age, causing a gradual reduction in vision, and mature cataracts involve the whole lens, leading to blindness. Surgical removal is the only effective cataract treatment. The procedure, called phacoemulsification, involves breaking up the cataract using ultrasonic waves, and removing the material via a vacuum. Horses who undergo the surgery require topical and systemic medications for about three months post-surgery.

Any changes you notice in your horse’s eyes should be evaluated by a veterinary professional to ensure their vision is not affected. If your horse is exhibiting any abnormalities related to their eyes, contact our team at Leatherstocking Veterinary Services, so we can provide the care they need and protect their vision.