The equine eye and how things can go wrong

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Eye diseases in horses can generally be managed with early recognition, assistance from your veterinarian in establishing a diagnosis, and effective treatment. Here are some of the most common issues. 

The horse has a uniquely developed eye suited to accommodate the lifestyle and needs of our equine companions. The location of the eyes being on the side of the head allows for a more panoramic view for protection. This is imperative to the fight or flight response as visual detection of a threat is necessary to alert the flight animals to flee.

An injured eyelid before suturing, pictured below.
An injured eyelid before suturing, pictured below.

There are a few common diseases of the equine eye that are worth having basic knowledge about. Early recognition and proper treatment is ideal to minimise damage to the eye. Eyelid cuts or lacerations can occur with contact of numerous objects, but most commonly occur with catching the eyelid on a metal S-ring on buckets or nails, or splits in the lid margin from blunt trauma. Eyelid lacerations are easily identified and repaired with primary closure or suturing.

Eyelid lacerations are easily identified and repaired with primary closure or suturing.
Eyelid lacerations are easily identified and repaired with primary closure or suturing.

The eyelids have an extensive blood supply and can bleed excessively. As long as the globe is not damaged, the eyelids have an excellent capacity to heal with minimal impact on ocular health. No matter how extensive the laceration appears, every attempt should be made to salvage as much eyelid margin as possible. Allowing the eyelids to heal without suturing can result in poor cosmetic appearance, enhanced scarring, and irregular eyelid margins. The scarring can result in hair or lashes contacting the cornea surface causing chronic irritation or discomfort.

Corneal injuries are one of the most common vision-threatening and painful eye diseases that occur in horses. The cornea is the front clear part of the eye that protects the delicate intraocular structures. Ulcers are generally due to abrasion or puncture with environmental objects (hay, branches, and sand). Clinical signs of a corneal ulcer include squinting, tearing, swelling around the eye, redness to the eye, and/or cloudiness to the eye. Corneal ulcers can be confirmed by careful examination of the eye and staining with a green dye (fluorescein).

Uncomplicated superficial corneal ulcers can heal without leaving any residual damage. Once an ulcer has occurred, the main concern is the risk of corneal infection. Topical therapy with antibiotics, as well as anti-fungal agents four times daily is recommended until the ulcer heals.

Corneal injuries are one of the most common vision-threatening and painful eye diseases that occur in horses.
Corneal injuries are one of the most common vision-threatening and painful eye diseases that occur in horses.

Bacterial and/or fungal corneal infections can be devastating and result in loss of vision and the eye.  These infections are more common in the southeastern United States with the heat and humidity supporting the growth of these organisms. If a corneal infection occurs, aggressive topical therapy up to every hour and in many cases, surgery, is necessary to save the eye.

Hourly medication can be quite difficult due to personal time constraints, and the horse will keep the eye forcefully closed because of the pain and light sensitivity. A subpalpebral lavage system can be placed for easier and more effective treatment.

This is a small tube or catheter inserted through the upper or lower eyelid with the injection port being attached to the mane near the withers. The lavage allows for medication to be injected through the catheter to reach the eye without coming near the horse’s head. Corneal infections in horses can take months to clear. Corneal ulcers can also be extremely painful, thus pain control with atropine and banamine will minimize discomfort and distress.

Equine recurrent uveitis or moon blindness is an inflammation of the iris that can be caused by trauma, infections in other parts of the body, the horse’s own immune system, or genetics, in the case of appaloosa and draft breeds.
Equine recurrent uveitis or moon blindness is an inflammation of the iris that can be caused by trauma, infections in other parts of the body, the horse’s own immune system, or genetics, in the case of appaloosa and draft breeds.

Equine recurrent uveitis or moon blindness affects horses worldwide. Uveitis is an inflammation of the iris (colored part of the eye) that can be caused by numerous issues. These include trauma, infections in other parts of the body, or can be generated by the horse’s own immune system, but there is also a genetic predisposition for Appaloosas and Draft breeds. Clinical symptoms of uveitis include a painful eye (squinting, tearing), cloudiness to the eye, and swelling around the eye. If uveitis is diagnosed, evaluation for infections or inflammations elsewhere in the body should be pursued. This may include bloodwork, titers for specific infections including Leptospirosis, abdominal ultrasound, chest radiographs, and sampling of fluid from inside the eye. If no underlying cause can be identified, the main goal is minimizing inflammation inside the eye to control pain and limit the impact on vision. Treatments that are used include topical steroids and nonsteroidal agents, oral steroids and nonsteroidal agents (banamine/bute), and atropine.

The frustrating part of this disease is the recurrent nature. The interval of flare-ups can range between days to years in patients. Management for horses affected with uveitis is to limit the frequency and severity of the episodes with lifelong treatment. This can be accomplished with daily maintenance medication (topical and/or oral) even when there is no active inflammation. If the eye is still having flare-ups, surgical implantation of a device impregnated with anti-inflammatory medication called cyclosporine allows for a constant release of drug into the eye to limit episodes. If the uveitis remains poorly controlled, further consequences including cataracts, glaucoma, and retinal detachment can result in loss of vision and a painful eye requiring removal of the eye.

Please contact your veterinarian if you notice any symptoms as soon as possible, as it may save your horse’s eyesight.

Article courtesy Palm Beach Equine Clinic 

Dr Susan M. Carastro

Susan M. Carastro DVM, MS, of the Animal Eye Specialty Clinic, is a Diplomate of the American College of Veterinary Ophthalmologists.

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