Horses have the largest eyes of all land mammals. They are prey animals and must be constantly aware of their surroundings. The position of their eyes enables them to see approximately 350 degrees. They have good day and night vision and can visualize blue, yellow, and green color patterns.
The cornea or clear part of the eye is one of the most sensitive tissues in a horse’s body. It is unique in that it lacks blood vessels and there is no pigment. It is composed of 4 layers with a combined total thickness of 1.0 to 1.5 mm. Damage to this portion of the eye is considered a medical emergency as the slightest abrasion (ulcer) to the cornea can rapidly threaten the future vision of that eye. Once the protective barrier of the cornea is compromised, bacteria and fungi invade and proliferate quickly due to the lack of blood vessels. Thus, early prevention is key!
Some of the more common medical conditions associated with an equine eye that can predispose it to a corneal ulcer include trauma, cancer, parasites, allergies, glaucoma, and uveitis.
Early corneal ulcers may not be visible without certain stains that adhere to the damaged portion of the cornea. However, there are outward signs that your horse will show to indicate a problem with an eye. These may include one or more of the following: tearing, excessive blinking, eyelid is held partially closed, cloudy cornea, abnormal head posture, or sudden face/head shyness. Due to the variable signs and sensitive nature of the cornea, it is important to seek early diagnosis and treatment if such a condition is suspected.