Injuries to the eye and surrounding tissues are common and should always be treated as potentially serious. Injury can result from direct trauma i.e. kicks or blows, grass seeds or thorns which can abrade or puncture the surface of the eye or from infection by parasites, bacteria or viruses. Owners should not be tempted leave a condition to ‘self-resolve’.
Some diseases are not an emergency but may be indistinguishable from potentially dangerous conditions or can progress over time to become much more serious if not appropriately treated. Veterinary attention should always be sought. An accurate diagnosis is critical to the successful management of eye disease.
NB Eye drops prescribed for one horse may not be appropriate for another horse showing similar signs.
Corneal ulcers are defects in the surface of the eye (cornea) often caused by infection, they cause inflammation, pain and irritation. Initial presentation is a closed, swollen eye, often running with tears. Your vet will diagnose corneal ulceration by putting a fluorescent dye into the horse’s eye. Affected areas will take up the dye and appear green. Infection may have started by a piece of grit or other direct injury such as a thorn.
Moon Blindness (Equine Recurrent Uveitis)
Moon Blindness is characterised by periodic bouts of acute pain and inflammation of the eye. When fluorescent dye is placed in the eye, there is no area of corneal ulceration even though the presenting signs may be very similar to corneal ulceration. Treatment with anti-inflammatory eye drops brings about apparent complete recovery but the condition may reoccur in the same or opposite eye in a few weeks or a few years.
There is no one particular cause of Moon Blindness. It is thought that there may be some inherited component to its occurrence but mild infection or allergy may also play a part.
Any change in the clarity of the lens is termed a cataract. Any opacity will interfere with the passage of light through the lens to the retina. Therefore, a horse with a cataract may experience anything from slightly impaired eyesight or complete blindness in that eye.
Cataracts can occur at an early age, known as developmental, or in older horses, known as degenerative. Developmental cataracts occur due to defects in the lens in the young animals and do not tend to get worse with time. Degenerative cataracts are a result of disease and tend to result, ultimately, in total blindness in that eye.
There is no treatment for cataracts in horses.
The conjunctiva is the outermost covering of the eye and inflammation can be caused by infection or direct injury. Typically, with conjunctivitis, the eye is swollen, painful and the surface looks red and sore. The eye may be running tears or, occasionally, pus. Presenting signs are similar to moon blindness or corneal ulceration. It is very important that an inciting cause be properly looked for and this must be done by a veterinary surgeon who may have to sedate the horse.
Entropion is seen in newborn foals and describes a condition where the eyelid and eyelashes turn in on the eyeball and cause irritation and sometimes ulceration. Treatment of the ulcer is by routine antibiotic eye-drops but the eyelid may need to be stapled in position or its shape corrected by surgery. Sometimes, simply correcting the abnormal position of the eyelid is sufficient to stop it reoccurring.
The ability to see relies on the proper functioning of multiple organs in the pathway to the brain. Any injury or malfunction of any of these steps may result in blindness. For example, cataracts prevent light reaching the retina, the retina may detach from the back of the eyeball or the optic nerve may be damaged or diseased. Only a veterinary specialist with the appropriate equipment may be able to diagnose the exact cause.
If you suspect that your horse may be blind, you can gauge its eyesight practically in a number of ways:
Menace response: When a hand is brought up sharply towards the eye the normal horse should flinch or display a blink response.
Obstacle course: animals can adapt to a loss of sight remarkably well and a horse that spends all of its time in the same surroundings may not show overt signs of blindness immediately. By leading the horse through a number of strange obstacles, defective eyesight will become obvious.
General behaviour will change. As the horse’s eyesight deteriorates, it will become less confident during exercise and may trip or fall more frequently