Common Equine Eye Complaints

How a Vet Examines a Horse’s Eye

In a darkened stable, an ophthalmoscope enables the vet to visualise the interior of the eye. An assessment of the following structures is performed:

• Cornea
• Anterior chamber
• Lens
• Iris
• Vitreous body
• Retina
• Optic disc

A normal, healthy eye will be open, clear and bright with no discharge. The conjunctivae will be pink and there will be no swelling present. A painful eye will present with some or all of the following signs:

• Blepharospasm (eye clamped shut)
• Lacrimation (tear overflow)
• Chemosis (swollen conjunctivae)
• Discharge (yellow, white or green)
• Photosensitivity (sensitivity to light)
• Corneal oedema (cloudy eye)
• Miosis (Constriction of the pupil)

If your horse presents any of the above clinical signs you should phone your vet immediately.

Common Eye Problems in Horses

Corneal Ulcers

This is a very common condition seen in all types of horses or ponies and is extremely painful. Your horse’s eye may be swollen, clamped shut, watering profusely and may have a cloudy appearance. Due to the pain he is experiencing, your horse will not allow you to open his eye manually and may strongly resist attempts to touch or open the eye.

A corneal ulcer is where the surface of the eye is damaged, usually caused by some kind of trauma or foreign body. Your vet will stain the eye to check for damage. An intact, undamaged cornea will not take up the stain whereas most corneal ulcers will stain green quite clearly.

Treatment may consist of frequent application of serum, antibiotics and pain relief direct to the eye. Oral pain relief medication may also be administered if required. Turn out is permitted only with a fly mask to prevent damage to the back of the eye from the sun and secondary infection from flies or dirt.

Some corneal ulcers can be very persistent so prompt veterinary attention is essential.

Equine Recurrent Uveitis

Also known as “moon blindness”, this condition is an important condition in that it can recur throughout the horse’s life causing significant painful episodes which, in extreme circumstances, can lead to the removal of the eye.

This condition is often mistaken for a traumatic injury due to the amount of pain the horse is in and the swelling around the eye. ERU’s primary cause can be a virus, systemic disease or trauma. It is thought to be an immune-mediated disease where the structures inside the eye are inflamed. Often debris can be seen in the front of the eye, the cornea may be cloudy and the pupil constricted. Examination with the ophthalmoscope is often resented due to increased sensitivity to light and the eye does not take up the stain.

Treatment consists of pain relief, topical steroids, antibiotics, serum and atropine (to dilate the pupil). This condition can be frustrating due to random repeat episodes causing significant pain and requiring aggressive treatment. It is thought that sunlight and wind can aggravate an episode so turn out is permitted only with adequate eye protection such as a fly mask with an eye patch sewn in.

Conjunctivitis

Also a common but not so painful a condition, conjunctivitis is a bacterial infection of the eye. As an owner you will find your horse has an ocular discharge which is usually yellow or green in colour. The conjunctivae will be inflamed and there may be some swelling but in general the horse is not too worried.

Your vet will stain the eye to check for corneal damage and may dispense antibiotic eye drops if they've ruled out any other problems such as corneal damage. It is recommended that sterile water / saline soaked cotton wool swabs are used to clean the discharge away twice daily. In the summer months, ocular discharge will attract flies which exacerbate the condition, therefore it is recommended the horse is turned out at night, or otherwise in a fly mask.

Blocked Tear Ducts

This condition tends to worry the owner more than the horse. It presents as a persistent, watery, ocular discharge which despite regular cleaning does not settle down. It usually occurs in the warmer months and is very obvious when the horse is brought in from the field.

There is no pain or swelling with this condition unless a secondary bacterial infection has occurred. There can be hair loss in the area where the watery discharge lies or just matting of the hair in this area. Normally tears produced by the eye, flow down the nasolacrimal duct and drains into the nose. However the tear ducts are very fragile structures which are lined with a soft membrane. If damaged, this lining can stick to itself and block the duct, resulting in an overflow of tears from the eye. Although not a serious condition, the ocular discharge does attract flies which in turn can cause a bacterial infection.

Two treatment options exist, the first is management rather than treatment. The eyes can be wiped clean twice daily with sterile, soaked swabs and a fly mask used whenever the horse is turned out. Antibiotic eye drops may be prescribed.

The second option requires the horse to be sedated so that the tear ducts can be flushed with sterile saline. This is not a painful procedure but the horse does feel some discomfort. Steroid / antibiotic eye drops are then dispensed to reduce any inflammation within the ducts.

Many horse owners feel happy managing this condition and tend to keep the flushing procedure as a back up plan. Flushing the tear ducts is obviously more costly and can be disappointing in that there may be a recurrence in the ducts becoming blocked.