Horse’s eyes are large and located on the sides of their heads for a reason; it gives them good peripheral vision. The ability to see all around them, even while grazing is important because they are prey animals, their best chance of survival is being on the move before a predator is anywhere near them. The location of their eyes also makes them prone to injury and disease, which can be devastating for the horse if left untreated. As horse owners, being aware of signs of pain, injury or disease is the best way make sure your horse’s eyes stay healthy.
Here are some things to be aware of:
• Are your horse’s eyes symmetrical? Do they look the same size? Shape? Are they both wide open and bright? The horse below has healthy eyes.
• Blephorospasm (squinting)? When a horse’s eye hurts, they squint and close the lid. The horse below has a painful eye.
Looking at the angle of the upper lashes of each eye is a great way to tell if they are squinting. If the lashes are pointing down, more than 45 degrees, it is a sign of pain. The horse above shows this in the right eye.
• Discharge of any kind? White, yellow, or green thick discharge should always be investigated, as should a lot of clear discharge from one eye.
• Loss of vision; is your horse suddenly spooking at more objects? Bumping into things? Cautious about entering a dark barn?
• Obvious trauma? An object in the eye or torn lids should always be seen immediately. It is important to carefully repair eyelid lacerations because the lids are important for distributing tears over the cornea and protecting the eye.
• Lumps or masses on the cornea or the tissue around the eye? Any horse can get them but horses with white around the eye and pink skin can be more prone to cancer.
• Excessive rubbing of the face or eyes?
If you see any of these signs, it is important to call your veterinarian right away. They will want to examine your horse because different eye problems are treated in very different ways.
Your veterinarian will first examine your horse’s eyes for symmetry, lumps or bumps, squinting or discharge. They will test reflexes to determine vision. Your vet might test your horse’s ability to produce tears. They may scrape or culture your horse’s cornea for bacteria or fungus. Next they will put a green/yellow dye called flourescein in the eye to look for abrasions or ulcers. Your veterinarian might dilate your horses pupil, this will allow them to see into the back of the eye and relieve some of the pain your horse may be experiencing. They will use a bright light to look at the anterior chamber of the eye, the lens and the back of the eye to see the retina and optic nerve. A lot of horses will require sedation and/or a nerve block or topical anesthesia to fully examine the eye.
Common Eye Disease
Entropion: Foals occasionally have the lower lid rolled inwards, this may cause the eyelashes to rub the cornea and cause an ulcer.
Traumatic Eyelid Laceration: It is important for your vet to see this injury immediately, to check for an ulcer and repair the lid , to ensure that tears are distributed evenly over the cornea. If not, your horse may experience dry eyes and be prone to ulcers. This is especially important in the upper eyelid.
Ulcers: Ulcers are scratches or defects in the horse’s cornea that can become infected with bacteria or fungus. They are very common in horses, causing severe pain and can be extremely serious . Prompt and appropriate treatment is necessary to save the horse’s vision and maybe even the eye. Minor ulcers can be treated topically multiple times a day. More serious ulcers may require a subpalpebral lavage system or a conjunctical flap to provide continuous treatment.
Squamous Cell Carcinoma: The most common tumor associated with the eye. The highest prevalence is in Belgians, Clydesdales and other draft horses, followed by appaloosas and paints. White, grey, and palomino hair coats are the most commonly affected. If your horse has small pink raised lumps on the lids or conjunctiva you should have them investigated. Multiple treatment options are available.
Equine Recurrent Uveitis (ERU): A diagnosis of ERU is made when a horse has multiple cases of uveitis. Uvetis is inflammation of the eye. The exact cause is usually unknown but the pathogenesis of this disease is immune mediated. Viruses, bacterial infections, trauma and intestinal parasites have all been linked to uveitis but it is very hard to isolate the organism from an affected horse. Most cases will only be in one eye but 20% of horses may have uveitis in both eyes. ERU is the most common cause of blindness in horses. Miosis aka a contracted pupil is a prominent sign, it is important to make sure that the miosis is not from an ulcer and that it is uveitis. Miosis can lead to a misshapen pupil and/or synechiae and/or cataracts. Secondary glaucoma can also occur. The most important thing about ERU is that it is a disease to manage carefully as it cannot be cured. Prompt treatment is the best way to preserve the structures of the eye and to preserve vision. Treatment may continue for weeks or months and should not be stopped abruptly just because the horse seems more comfortable.
Cataracts: Cataracts are opacities of the lenses that obstruct vision minimally or can be the cause of complete blindness in that eye. They can be inherited, traumatic, or secondary to nutritional problems or ERU. Cataracts from old age do not occur until a horse is at least 20 years old, they do affect vision. This is in comparison to nuclear sclerosis which causes cloudiness but does not affect vision.
Most Common Eye Diseases by Breed:
Equine Recurrent Uveitis (ERU)
Congenital Stationary Night BlindnessArabian
Congenital CataractsBelgian Draft
Squamous Cell CarcinomaMiniature Horses
Aggressive Sarcoid (of the eyelid)
Aniridia (absence of the iris)Paso Fino
Congenital Stationary Night Blindness
Rocky Mountain Horse
Cataract, lens luxation
Retinal Dysplasia, retinal detach-ment
Anterior Segment Dysgenesis*
Progressive Retinal Atrophy