Horses are prey animals and so their behaviour is certainly related to their vision. A horse’s eyesight is adapted so that it can survive in the wild where there are large numbers of dangerous predators. Thus, the horse has successfully evolved to spot these predators more rapidly.
What do horses see?
As opposed to humans, horses have eyes on the side of their heads thus making their vision different to our own. Unlike us, they can see approximately a massive 350° around themselves, 285° being monocular vision and 65° being binocular visions. Monocular vision is what can be seen using only one eye and binocular vision describes the vision seen by both eyes, where their sight overlaps. A horse’s depth perception is therefore less than that of our own.
Of course, the horse has blind spots where it cannot see. One such area is straight in front of the horse and behind its head. Because of this, if a horse wishes to see straight at an object it perceives as a threat, owners will notice that their horse arches its neck and lowers its head. In order to see objects further away from the horse, it will raise its head.
In terms of colour vision, horses are less able to distinguish between red and green than humans. In spite of having a better acuity in daylight than humans, they actually have better night vision than us due to the fact that they have more rod cells in their eyes. Rod cells allow for sight in lower light intensities, and rod cells in higher light intensities.
What should a healthy horse’s eyes look like?
A horse’s eye is one of the largest of all the mammals. There eye should be bright and alert, with no visible abrasions on its surface. There should be no discharge from the eye of foreign objects such as pieces of hay or straw. The eye should not be swollen and, of course, no ulcers are present on healthy eyes. The eye should not be cloudy or red in appearance.
What problems can horses’ eyes have?
A horse’s eye can be affected by a variety of problems although some horses can live a full life without experiencing any. Despite this, it is strongly encouraged that owners should at least be aware of any possible problems that can occur with the eyes of their horses and ponies.
Corneal Abrasion and Ulcer
A corneal abrasion is simply when the surface of the cornea is scratched or damaged. This can later lead to a corneal ulcer which is where a layer, or layers, of the cornea is damaged. The cornea can be described as the clear windshield of the eye. The horses may partially close its eye in pain, show signs of redness or cloudiness, rub the eye constantly with its leg, or the affected eye may produce excessive tears.
The condition of a corneal ulcer may be diagnosed by a veterinarian by observing the symptoms, followed by the use of a fluorescent dye which shows up the presence of any ulcer by turning it green. The pain and swelling can be reduced with the use of atropine ointments. An infection is prevented by being treated with an antibiotic, prescribed by the veterinarian.
Cataracts in horses occur when the lens becomes more cloudy or opaque. The size and cause of the cataracts can differ. A congenital cataract is where a horse may be born with the condition and a juvenile cataract is where it can develop in young horses. More commonly, mature horses become affected with this condition, usually due to trauma or as a secondary problem. Although treatment depends on the type of cataracts and variety of other factor, surgery has proved to be successful in many cases. Despite this, their vision will not be as good as it was before they had the condition.
When the conjunctiva of the eye, which is the lining of the inside of the eyelids, becomes inflamed, this is known as conjunctivitis. The eye may become red and swollen and pussy discharge may be visible. Behavioural symptoms include rubbing the eye. There are many causes of this condition including trauma, allergies, tumours, and infections from bacteria, viruses, fungi or parasites.
Equine Recurrent Uveitis
Simplified as (ERU), this occurs when the uveal tract becomes inflamed. It is very painful and lasts for a very long time. This can be caused by a combination of factors, as a horse with uveitis does not necessarily have Equine Recurrent Uveitis. These factors include traumas or bacterial infections.
This can occur as a tumour found around the affected horse’s eye, although other parts of the body may also be affected. If diagnosed, these should be removed as quickly as possible by a veterinarian. The tumours can appear like warts and occur singularly or in clusters. Sarcoids can be easily mistaken and even misdiagnosed for other skin problems.
Obstructed Tear Duct.
The tear duct runs down to the nostril from the eye of a horse. If this becomes obstructed then a pussy discharge will become visible from the eyes as a result of an infection. Additionally, inflammation can be the cause as well as tumours, and trauma. The duct can be flushed by a veterinarian which is often a successful procedure.
How do I keep my horse’s eyes healthy?
Clearly, it is very important for horses to maintain healthy eyes. The horse should ideally be kept in an area with as little dust as possible as these can lead to, sometimes severe, irritations of the eye. Checking a horse’s eye is vital to ensuring it is healthy. Check the eye for discharge, swelling, cloudiness, or foreign debris.
If owners suspect that their horse or pony has an eye infection or problem then the vet should be contacted in order to ensure that the problem, if there is any, does not worsen. Catching an eye infection in its early stages can protect the horse from devastating problems such as blindness.