It’s not uncommon for horses to experience eye problems. Several conditions and diseases can affect vision and eye health in horses, including uveitis, cataracts, and conjunctivitis.

Horses experiencing eye issues may have symptoms such as swelling, tearing, drainage, discoloration, cloudiness, or sensitivity to light. Some conditions may not affect the eye, but instead, the eyelid or area around the eye. 

If your horse is affected by vision problems, this may result in poor performance, reluctance to move, nervous behavior, stumbling or clumsiness and an increased risk of injuries.

If your horse shows signs of any eye problems, have him evaluated by your veterinarian as soon as possible. With many eye conditions, early diagnosis and treatment will improve your horse’s prognosis and decrease recovery time and financial burden for the horse owner. [1]

The Horse’s Eye

The eye enables visual perception, so the horse’s brain can interpret its surroundings.

Horses have large eyes and horizontally elongated pupils to allow for maximum light capture.

Equine vision is adapted for peripheral motion detection and low light conditions.

This is attributed to their evolution as a prey species and their need to constantly monitor their environment while grazing. [3]

Anatomy

Damage to any one of the eye’s intricate structures can affect the rest of the eye and how it functions. [2]

The wall of the horse’s eye is composed of three layers: [3]

  1. An outer, fibrous tissue layer made up of the sclera (the whites of the eye) and the cornea (clear dome in the front of the eye);
  2. A vascular tissue layer called the uvea which is made up of the iris (colored part of eye), the ciliary body behind the iris, as well as the choroid which sits underneath the retina; 
  3. An inner layer of nervous tissue that makes up the retina

Parts of the Eye

Other important parts of the eye that can be affected by eye conditions include:

  • The pupil, the hole in the center of the iris through which light passes; 
  • The lens, a disc-like structure that sits behind the iris and pupil and is held by ligaments attached to the ciliary body;
  • A space in front of the lens filled with a clear, watery fluid called the aqueous humor. This fluid bathes the lens and cornea, bringing oxygen and nutrients to these structures and removing their wastes;
  • A large space behind the lens filled with a clear, gel-like fluid called the vitreous humor, which holds the retina in place;
  • The conjunctiva, a protective layer of tissue that covers the sclera and lines the inside of the eyelids as well as the third eyelid;
  • The lacrimal glands, which produce tears to keep the surface of the eye lubricated.
  • The orbits are the bony structures in the skull that house the eyeball, extra-ocular muscles, nerves, blood vessels, lacrimal glands, and fatty tissue. 

Understanding Equine Vision

Light enters the horse’s eye by passing through the cornea, aqueous humor, lens, and vitreous humor which are all clear. These structures also focus light on the retina by bending it.

Light then passes through the retina and gets converted into an electrical impulse. This signal travels through the optic nerve to the brain where it is interpreted into vision. [3]

Signs of Vision Problems

If a horse is experiencing vision problems, it may affect their performance as well as their overall well-being.

Signs of an eye condition affecting a horse’s sight may include:

  • Clumsy behavior
  • Self-trauma
  • Reluctance to move (especially from a lighted area to a dark one)
  • Spooky behavior
  • Head shaking

Additionally, horses with vision problems may be bullied by more dominant horses in their grouping. [3]

Mad About Horses
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