7 Eye Disorders that Affect Horses

7 Disorders of the Equine Eye

The Eyes Have It

There are so many illnesses and diseases that can affect the health of a horse. Today’s post is the beginning of a series of posts that are going to discuss the different health issues that horses can develop and how each part of the horses body is affected.

“When a horse greets you with a nicker and regards you with a large and liquid eye,
the question of where you want to be has been answered.”

~ Author Unknown

Today’s post is going to focus on the those beautiful eyes that we love.

Diagnosis of a vision problem begins with a complete eye exam. In some cases referral to a veterinary eye specialist (ophthalmologist) is necessary. Ophthalmologists have expertise in the diagnosis and treatment of eye diseases. If the cause of the visual disturbance is not evident on examination alone, an electrical test of retinal function (electroretinogram or ERG) may be required. Refraction to look for near-or far-sightedness is also done if necessary.

Common Disorders of the Equine Eye

7 Disorders of the Equine Eye #horses #peachwood #eyedisorders

Corneal Ulcers

Corneal ulcers are one of the most common acquired ocular diseases in the horse. A corneal ulcer is a break in the surface layer of the cornea. Ulcers usually develop secondary to trauma, often from plant material; for example: tree branches, straw scratching the eye.

Early detection and appropriate therapy of a corneal ulcer will reduce the chances of a serious complication such as loss of the eye.


Signs of a corneal ulcer include:

  • redness of the eye
  • tearing
  • squinting
  • opacities in the cornea
  • and roughened or irregular areas on the corneal surface.


Veterinarians diagnose corneal ulcers using fluorescein staining.


Uveitis is inflammation of the uveal tissue inside the eye.


The clinical signs of uveitis include:

  • redness of the eye
  • squinting
  • tearing
  • cloudiness of the cornea or ocular fluid
  • a small or constricted pupil
  • iris color changes (e.g. yellowing of a normally blue iris or darkening of a brown iris).

Uveitis is treated with topical and oral anti-inflammatory medications and drops to dilate the pupil.

Equine Recurrent Uveitis

Equine recurrent uveitis (ERU) is uveitis that reappears over and over with new episodes triggered by the immune system. In some horses, rather than recurring episodes of overt inflammation, there is ongoing, low-grade inflammation that is never resolved. With this ongoing or recurring inflammation, permanent damage is done to structures inside the eye. This includes the iris becoming stuck down to the lens, cataract formation in the lens, corneal scarring, retinal detachments, retinal scarring, and retinal and optic nerve degeneration. Eventually, these changes lead to permanent blindness.

ERU is the most common cause of blindness in the horse and it is a painful condition.


This is a condition in which the fluid in the eye cannot drain properly and builds up causing increased pressure inside the eye. This leads to permanent damage to the retina and optic nerve and eventual blindness. Glaucoma may occur on its own, but is most commonly a secondary effect of chronic or recurrent uveitis in the horse.


Some of the most common clinical signs of glaucoma include:

  • redness
  • tearing
  • a cloudy cornea
  • a dilated or enlarged pupil
  • an enlarged globe
  • vision loss


Cataracts are opacities within the lens. They may be small and cause very little visual disturbance, or they may involve more of the lens and cause blindness.


The clinical signs of cataracts include:

  • a white lens or
  • white discoloration in the pupil opening.

Cataracts may be inherited or occur secondary to trauma, or chronic inflammation (such as a consequence of ERU). Some foals are born with cataracts (congenital cataracts) and these may be inherited but may also occur related to maternal or environmental influences (maternal fever, poor nutrition, toxin exposure during pregnancy etc.).

Squamous Cell Carcinoma

This is the most common cancer of the equine eye region.

It occurs commonly on:

  • the third eyelid
  • conjunctiva
  • cornea
  • eyelids and may spread to involve the orbit.

Older horses, those with white skin around the eyelids, and those exposed to ultraviolet light are most at risk. The tumor may appear as a pink, raised, roughened mass. It may also appear as erosive sores when involving the eyelids. It is common for this tumor to spread into local tissues, and it may spread to distant sites as well. Treatment depends on the location and size of the tumor.

To see pictures of these conditions, click here.

Corneal Lacerations

Most often lacerations are due to a blow, like a kick or running into a fixed object. This is an immediate emergency and is most often referred to an ophthalmologist or a surgeon to achieve the best results.

Clinical signs include:

  • a prolapsed iris
  • hyphema (blood inside of the globe)
  • hypopyon (pus in the eye)
  • photophobia – extreme sensitivity to light.
  • epiphoria – a watering of the eyes due to excessive secretion of tears or to obstruction of the lacrimal passages.
  • swollen eyelids
  • squinting
  • and most often there is a defect on the cornea.

Treatment is focused on decreasing further damage to the intraocular structures of the eye and repairing the integrity and pressure of the globe.

It is interesting that horses can have the same eye disorders that we can. Let’s keep an eye on our horse’s eye and keep them healthy!