Equine eyes are a complex and delicate structure, perfectly located on the side of the head to allow almost 360 degree vision. Unfortunately, this complexity means that there are a multitude of problems that can occur with the various structures that form the eye. These problems can start off relatively minor, but horses are extremely sensitive to injury and disease of the eye and so the situation can rapidly escalate into something much more serious. This is why it is always worthwhile seeking veterinary advice if your horse develops any issues with their eyes.
Below are some of the signs to watch out for that may indicate a problem with your horse’s eye:
• Blinking a lot or squinting
• Sensitivity to light
• Cloudiness in the eye
• Excessive tear production/watery eyes
• Swollen/red conjunctivae
• Discharge(which may be yellow, green or white)
• Constriction of the pupil
The following are some conditions frequently encountered affecting the equine eye.
Conjunctivitis is inflammation or infection of the conjunctiva, which becomes red and swollen, often with a thick sticky yellow/green discharge as well. Infection may be bacterial, viral, fungal or parasitic. Treatment depends of determining the causative agent and may consist of antibiotic or antifungal eye drops, steroid eye drops, deworming or even surgery. Whatever the cause, it is advisable to clean the eyes of discharge frequently with damp cotton wool and to turn out in a fly mask during warm weather.
The cornea is the very outermost layer of the front of the eye, making it the first line of defence against anything entering the eye and thus rendering it very susceptible to damage from trauma and foreign bodies. Any damage to the cornea is referred to as an ulcer and is often very painful, typically causing excessive watering and blinking of the eye, swelling and cloudiness.
A stain applied to the eye will help diagnose an ulcer as a normal eye will not take up the stain whilst a damaged cornea will stain an obvious green colour. Antibiotics and anti-inflammatories applied directly to the eye are the mainstay of treatment, though oral pain relief may be indicated if the condition is serious enough. The horse should wear a mask to protect the eye during turnout and frequent check ups may be required as some ulcers can take a long time to fully resolve with more intensive treatment occasionally necessary.
Equine Recurrent Uveitis
Often called Moon Blindness, this is a relatively common condition that has the potential to be very serious. Uveitis is inflammation of the uveal tract, which is composed of the iris, ciliary body (produces the fluid inside the eye) and choroid (outer part of eye containing blood vessels). It can occur secondary to a separate condition such as corneal ulcers, or it can be a primary disease process as is the case in equine recurrent uveitis.
The underlying cause of ERU is not known with various suggestions having been made, from bacterial or viral infection to trauma or auto-immune disease, but nothing conclusively proven. Genetics play a role with certain breeds (e.g. Appaloosas) showing an increased susceptibility.
Diagnosis involves detecting inflammation of the uveal tract without finding any other discernible cause after thorough examination of the eye. Signs consistent with ERU include constricted pupils, debris inside the eye and cloudy/blue corneas.
Treatment of an acute flare up can challenging with a combination of drugs often required. This can include steroid eye drops for the inflammation, atropine to dilute the pupil and relieve pain, antibiotics eye drops if infection is present and systemic anti-inflammatories such as flinixin to further help with pain and inflammation. Once again a mask to protect the eye and reduce irritation is helpful.
Unfortunately, the occurrence of this condition cannot be predicted. Some horses may suffer infrequent attacks that can be managed well with the treatment recommended above. However, some individuals can have such severe and frequent bouts that removing the eye may be the kindest option. ERU often results in increased pressure inside the eye which can also ultimately lead to blindness.
Blocked Tear Ducts
This problem is usually indicated by persistently watery eyes occurring especially during warmer weather. Normally tears drain from the eye into the nose via the nasolacrimal or tear ducts. However, these ducts are quite delicate and if damaged can become obstructed, preventing the tears from draining properly. Consequently the tears overflow from the eye causing wet patches and possible matting of the hair or even hair loss under the eye. This condition is not necessarily a great cause for concern, but the discharge from the eyes can attract flies which can introduce bacteria that may then result in infection of the eye.
Cleaning the eyes regularly with sterile damp cotton wool and using a fly mask may be sufficient to control this problem with antibiotic eye drops provided if secondary bacterial infection does occur. Many owners manage their horses this way. It is also possible to flush the tear ducts with sterile saline, a procedure that must be done under sedation as it does cause some degree of discomfort. Unfortunately, there is potential for the ducts to become blocked again in spite of flushing.
Cataracts are where opacity forms in the lens of the eye, which is located just behind the iris and is responsible for focusing light onto the retina. This opacity usually occurs as a result of disease (such as ERU) and is generally progressive over time causing increasing loss of vision. Some cataracts may be congenital or developmental, occurring in young foals. Tell tale signs of either kind of cataract include milky white pupils and poor eyesight. It is possible to surgically remove the lens of the eye, thus removing the visual impairment caused by the cataract. Without the lens to focus light, the horse will be permanently long sighted in the affected eye, but most individuals cope with this without any problems.
Squamous cell carcinomas are the most frequently seen tumours of the eye and can occur within the eyelid, on the surface of the eye or on the third eyelid. They are usually quite obvious as wart-like growths.
Treatment of a tumour on the surface of the eye typically requires referral to an ophthalmic specialist for removal followed up by cryotherapy (freezing) or radiation therapy. A tumour on the third eyelid usually requires removal of the entire third eyelid, a more straightforward procedure often done in general practice. Tumours within the eyelid are the trickiest to deal with, but again surgical removal followed by further treatment such as chemotherapy is the best option.
Sarcoids and melanomas are two other growths that can potentially affect the eye and surrounding structures.
If you have any questions about eye diseases in horses, or have any concerns about whether your own horse may be suffering from eye disease, contact your vet for advice.
If you have any questions about any aspects of your horses’s health, or indeed your pet, farm or smallholding animals, please do not hesitate to contact us on 01892 835456. Putlands Veterinary Surgery is based in Paddock Wood in Kent, and offers a friendly, proffessional and personal service for all species of animal. We have four dedicated large animal vets with a wealth of equine experience between us, and are always happy to help