Earlier this year, an Italian racehorse called Laghat hit the headlines all over the world when he topped €100,000 in winnings, despite being blind.
Blinded by a fungal infection as a young foal, the nine-year-old thoroughbred clocked up wins in 19 races, even though he can see only shadows.
Eye problems in horses can be caused by injury and disease, and even small eye problems can develop into much bigger issues.
The University of Davis in California, USA, is one of many research institutes worldwide that study and treat eye problems.
Some of the most common eye problems in horses its staff have found are traumatic injuries, corneal disorders, uveitis (inflammation inside the eye), cancer and cataracts.
Traumatic injuries can vary in severity from simple abrasions of the eyelids to full thickness lacerations of the eyelids or cornea. Abrasions of the eyelids can be treated with first aid, followed by veterinary treatment.
Lacerations of the eyelid or cornea will result in the horse squinting, with discharge from the eye, ranging from excess tears, mucus or blood. All of these should be considered an emergency and require the immediate attention of a vet. The long-term prognosis depends on the structures injured.
Eyelid lacerations are usually very obvious, with the torn lid hanging loose and blood on the face around the eyelid. Immediate attention from the vet is essential to repair the eyelid and protect the cornea.
Corneal lacerations are often less obvious because the only clinical sign may be intense squinting. The vet may need to use sedation and/or nerve blocks to examine the damage.
Foreign objects such as grass seeds, dust, sand or ash can get lodged under a horse's eyelids. Flushing with saline solution might help, but the vet should still examine the eye for any further damage.
If a foreign object such as a thorn has pierced an eyelid and become embedded, you can remove it, but follow up with a full eye examination with a vet to determine whether further damage has occurred.
If the eyeball itself has a foreign object embedded in it, do not attempt to remove it: seek immediate veterinary attention because surgery may be required.
Corneal ulceration is the most common problem that occurs with the cornea of the eye. In this condition, the most superficial cells of the cornea are abraded away.
Like most eye problems, corneal ulceration is most often seen as a suddenly painful eye, with excessive tears forming.
Corneal ulcers require immediate care by a vet because they can get worse very quickly. The cornea does not have blood vessels running through it to help clear an infection, so the eye is more susceptible to infection from bacteria and fungus.
Sometimes a minor wound to the cornea may occur and appear to have healed, but an infection in the deeper layers of the eye can lead to corneal infection. Again, this requires immediate treatment by a vet.
Uveitis or inflammation inside the eye is a common cause of blindness in horses. Equine recurrent uveitis (ERU) is when a horse suffers recurrent bouts of eye inflammation, seen as squinting, redness, cloudiness and tearing in the eye.
The severity of the signs and the frequency of the ERU attacks vary between horses, but blindness results as a consequence of cataracts, glaucoma and retinal degeneration caused by repeat episodes.
The most common eye cancer seen in horses is squamous cell carcinoma. These tumours typically occur in one of three locations: on the surface of the eye, on the third eyelid, or within the eyelid. These masses are often readily visible and have a wart-like appearance.
It can be treated using surgery to remove the mass, freezing or radiation treatment.
Other types of cancer such as sarcoids and melanomas, which are common throughout the body, can also affect the eyes. In most cases, the tumour can begin as a small area of roughened eyelid or a small bump. If diagnosed early, a number of treatments can be used.
The lens of the horse's eye is a flattened, transparent, flexible disc consisting of layers of lens fibres. The lens sits behind the iris and helps focus the images on to the retina. A diseased lens usually responds by becoming opaque or cloudy. This cloudiness can be seen in part or all of the eye. Cataracts are often progressive in nature and result in serious visual loss over time.
Horses can be born with cataracts through developmental or heritable causes.