To a horse, vision is essential
They must be able to see danger and react quickly using monocular vision on each side to constantly scan the environment for possible threats, and the binocular vision to focus on an object in front of them such as an upcoming jump. This gives them an almost 360o
field of vision.
Any injury to an eye can be devastating
to a horse as they lose awareness of their surroundings. Eye conditions can deteriorate rapidly in horses going from mild to severe within hours. They are also incredibly painful as anyone who has ever scratched their eye can vow. Signs of pain in a horses’ eye include holding the eye shut, producing a lot of tears and swelling around the eye. It is critical to call your veterinarian as soon as you see any of these signs.
Corneal ulcers are the most common eye problem we see and often the result of direct trauma or from objects stuck in or on the eye. The following horse was floated for several hours and arrived at the new property with a painful eye. On examination, a piece of hay was found stuck to the cornea (Figure 1)
After the piece of hay was removed, fluorescein stain was applied. This will only stick to an area of the cornea that are damaged and is the best way to detect ulcers. If you look closely at Figure 2
, there is a faint green outline where the piece of hay was. If this had been left much longer then it is likely the entire area where the hay was would be ulcerated, significantly prolonging healing time and cost of treatment. We can see in the pictures that already the pupil was small from pressure build up due to inflammation.
This next horse spooked and caught his eye on a piece of spouting. This caused an ulcer across his entire eye (Figure 3). This is a much more significant ulcer than the previous case so required a more intensive treatment regime but due to quick identification of an injury by the owner and early treatment by a vet, it healed completely within a couple of weeks. The two main treatments for any eye ulcer are an antibiotic ointment
and Atropine, which reduces inflammation in the eye but also causes the pupil to remain dilated. A dilated pupil in sunlight is very painful for the horse – imagine if the feeling of turning the light on first thing in the morning stayed all day! For this reason, and to prevent the horse further damaging the eye, we use eye masks which the horse can wear in the paddock (Figure 4)
It is important to note that these ulcers were caught very quickly and had good outcomes.
Corneal ulcers are at very high risk of infection and the main bacteria produce enzymes that cause the surface of the eye to literally melt away, known as a “melting ulcer”. This condition requires intensive treatment and may even require surgery. At the end of treatment, the eye will be left with a permanent defect which will hinder vision.
Uveitis is another condition of horse eyes. Uveitis is inflammation within the eye and causes the muscles that control pupil size to go into spasm, leading to a painful constricted pupil. Uveitis will usually respond well to atropine, which relaxes the muscles and allows the pupils to dilate, and topical steroids. Some horses are predisposed to uveitis and it will continue to occur in them.
Any damage to a horse’s eyelid is a serious condition (Figure 5). Horses require the eyelids to remain intact in order for normal blinking and tear production. If this is compromised then the horse can permanently suffer irritated dry eyes which predispose it to the above conditions and may also result in eventual blindness. If the eyelid is damaged in any way, even if you don’t think it is significant, then it is important to get veterinary attention.
Remember that the injury could have also damaged the eye.
In summary, eye injuries in horses are considered emergencies and need to be seen by a veterinarian as soon as possible. It is essential that the eye has been properly examined before anything is put onto the surface of the eye, as the wrong treatment can cause severe deterioration and worsening of the condition. Always consult your veterinarian if you are concerned and never self-treat an eye condition.