Equine eyesight is particularly sensitive, with even the smallest injury quickly leading to disease and then blindness. It should therefore be of no surprise that at Equis Veterinary Practice we consider the successful treatment of equine eye conditions to be of the utmost importance.
Clinical signs of eye disease.
A horse showing any or a combination of the following signs should be examined by a veterinarian as a matter of urgency:
- Pain, which leads to partial of complete closure of the eyelids
- Excessive tear production
- Swelling of eyelid/s
- Redness
- Rubbing the eye
- Change in corneal appearance – a normal, healthy cornea is clear, while an unhealthy one may become blue/cloudy
- Differences in pupil size between eyes
- Flecks of material in the fluid of the eye.
Common conditions.
Corneal disease or injury.
Probably the most common eye condition associated with horses, corneal disease or injury is essentially damage to the surface of the eye. While the eyelids and lacrimal system work to protect the eye, it is the cornea that has the most important barrier function, protecting the deeper structures of the eye from micro-organisms. Damage to this area is, more often than not, due to the exposure of the equine cornea to harmful agents.
Corneal ulcerations
A corneal ulcer occurs when there is loss of corneal epithelium. Common causes of corneal ulceration including: direct trauma, foreign bodies, eyelid dysfunction, eyelid tumours, and abnormal or extra growth of eyelashes that may scratch the cornea. The most common cause, however, is a scratch to the surface of the eye.
Horses can scratch their eyes easily while grazing in tall grass or shrubbery. Another common method, particularly among race horses, occurs when dirt is thrown into the face and eye by another horse. The result is a superficial ulceration of the cornea.
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Simple, uncomplicated corneal ulcerations usually heal quickly, however, many ulcers are complicated by infection. The surface of a horse’s eye is typically rich in bacteria and fungi. Not to worry – under normal conditions these bacteria are harmless to the eye. In the case of corneal ulcers, however, the bacteria and fungi may enter the ulceration, causing it to extend through the full depth of the cornea, eventually rupturing the eye and blinding the horse. So, as you can see, an otherwise simple scratch can quickly become a vision-threatening condition. We therefore recommend that all corneal ulcers receive immediate veterinary attention.
When treating an simple and uncomplicated ulcer, we focus on the prevention of infection while we wait for the cornea to heal. In more complicated cases, when infection has already occurred, the infecting bacteria and fungi are aggressively attacked through treatment with anti-microbials. In the most severe cases, this treatment may involve treatment every two hours, around the clock.
Melting Ulcers
If left to run amok, the infection and severe inflammation typically associated with a deep complicated ulcer can quickly lead to a “melting ulcer”. A “melting ulcer” is an uncontrolled infection or inflammatory response in the stroma that leads to liquefaction of the cornea. Melting ulcers are not uncommon in horses and constitute a genuine ocular emergency because of how quickly the cornea may perforate.
Herpes keratitis
Herpes keratitis is the only recognised infectious cause of equine corneal ulcers. Infection of the eye with the Herpes virus can result in the development of pinprick ulcers in the cornea. These can easily be treated with topical antiviral medication.
Stromal abscesses
A stromal abscess occurs when a small pinprick ulcer becomes infected with bacteria and/or fungi. The ulcer heals quickly, trapping the infection within the deep layers of the cornea, a.k.a. the stroma. This type of ulcer differs from other infected ulcers because the epithelium of the cornea remains intact – which is also why treatment of stomal abscesses is difficult.
Treatment of stromal abscesses is challenging as many medications struggle to penetrate into the abscess. Medical treatment of stromal abscesses may take up to two to three months and a treatment tube should be inserted to ensure easy medication. Occasionally surgical intervention is indicated.
Habronema
Another important disease of the eye results from a Habronema infection. Such infections occur when flies lay eggs onto conjunctiva, which then develop into microscopic maggots. Initially the infected eye may appear like conjunctivitis, but examination by a veterinarian will confirm infection by maggot. Treatment includes the physical removal of the maggots, followed by application of specialised mediation.
Help prevent infection by regularly deworming your horse or pony with Ivermectin.
Conjunctivitis
Conjunctivitis is a common term that most people use to describe a red and irritated eye. It actually means inflammation of the conjunctiva and can be caused by bacterial, viral or parasitic infection, irritation from flies or even a dusty environment. An eye with conjunctivitis should not be painful. While it may appear that conjunctivitis is common and not an emergency, it is often a symptom of another underlying eye disease.
Eyelid lacerations
It is not uncommon for horses to injure their eyelids, but it is essential that all efforts are made to repair the damage as soon as possible. Failure to do so can lead to undue pain, corneal irritation, and chronic weepy eye.
Eyelid Tumours
Tumours that arise on, or near, the eyelids may encroach on the cornea resulting in chronic irritation and the possible ulceration of the cornea. Before these problems occur, it is recommended that the tomour be surgically removed and/or treated using chemotherapy. It is essential that treatment is sought as soon as a tumour is identified, as the attempted removal of a large tumour can result in the creation of defects that would impede the eyelids ability to protect the eye.
Squamous Cell Carcinoma
Squamous cell carcinoma is a common eyelid tumour in horses – especially in those less pigmented breeds like Paints and Appaloosas. Early in its development the disease resembles a low grade inflammation, with a slight mucous discharge and reddening often occurring. As it progresses, the carcinoma becomes more vegetative-like and may even begin to ulcerate. Lesions may also be found on the eyelids, including the third eyelid.
Lesions, particularly on the third eyelid, can be treated by the use of a topical atropine. Because even minor damage to the cornea can cause a reflex uveitis, dilating the pupil is an important part of this treatment. Surgery may be called for, should deeper corneal ulcers develop. This surgery will help to protect the cornea from damage, promote healing, and reduce the risk of perforation.
When it comes to squamous cell carcinoma related surgery, options include conjunctival graftin, and temporary tarsorraphy.
Performed under general anaesthesia, conjunctival grafting is a process whereby the conjunctiva is surgically transplanted onto the defective cornea. This is done by loosening a small flap of the conjunctiva and then pulling it to cover the entire cornea. The purpose of these grafts is to provide the cornea a direct blood supply, thereby promoting its healing. The grafts also provide structural support to areas with extremely thin cornea. Once the cornea has healed, the graft may be surgically trimmed to reduce the area of scarring.
A temporary tarsorraphy is a common procedure wherein the eyelids are temporarily sutured together to provide protection for the diseased eye. Although it may sound simple, this technique dramatically improves healing. That being said, it does however have its down side. Having the eyelids sutured together makes it difficult to apply any medication directly to the eye. You may therefore find that your vet will choose to insert a treatment tube through the eyelids so as to administer medication directly to the eye.
Bullous keratopathy
Bullous keratopathy is a non-specific diagnosis that describes the formation of severe corneal oedema that give the appearance of the cornea hanging over the lower eyelid margin. This condition results either from an extensive shallow ulcer that allows fluid to enter the corneal stroma from the tear film, or from the occurrence of a blunt trauma that damages the edothelium and causes fluid from inside the eye to penetrate the cornea. Although scary to look at, it is manageable if treated as an intensive medical condition.
Uveitis
Particularly prevalent among Appaloosas, who are genetically predisposed to the disease, Uveitis is the most common cause of blindness in horses. Uveitis is a technical term used to describe the inflammation of the internal structures of the eye. It is an extremely painful condition and, although more commonly known as a secondary condition associated with ocular injury or disease, it can sometimes be the primary reason behind the horse’s discomfort.
In caring for an eye afflicted with Uveitis is is essential that the underlying disease first be identified and treated. If no such primary infection is eivident, then symptomatic treatment of the Uveitis is necessary to relieve pain and reduce the chance to permanent damage to the eye. Should our vets be unable to prevent a loss of vision, then we will implement a treatment protocol that will include eliminating the pain, and minimising owner expense and effort. Often the best way to achieve this is the surgical removal of the eye. Enucleation – a surgical process that removes the eye, but leaves the affiliated muscles and orbital contents in tact – has very few patient side effects and, once surgery-related pain has subsided, leaves the horse comfortable and free to live a long, healthy life.
Treatment
When it comes to the treatment of equine eye conditions, the main hurdle to effective care is the horse itself. Eyes requiring intensive treatment are painful and so it can be very difficult, if not impossible to, effectively and consistently apply the required medication. That is why Equis Veterinary Practice is committed to providing you and your horse with a treatment regime that is not only effective, but also as painless as possible.
Equine eye diseases may be treated medicinally or surgically, depending on the condition with which the horse is affected. Treatment may, however, include:
- Resolution of the primary cause of disease e.g. foreign body removal.
- Administering broad spectrum antibiotic/ antifungal directly to affected eye to treat a microbial infection.
- Pain management through the use of pain killers and anti-inflammatories
- Surgery