A nod is as good as a wink to a blind horse

News
Mar 25, 2011

In his forward to the 1943 edition of his book "Home Veterinarian’s Handbook," E. T. Baker, DVM, states: "An emergency has been defined as ‘a sudden condition requiring immediate action.’" His book listed over 700 subjects on what might ail a farm animal, including equine eye injuries. Baker definitely considered this malady an emergency. He outlined emergency first aid, while stressing the importance of calling a veterinarian at once whenever possible. Basically ... call the operator and have her get the vet on the line.

Almost 70 years later, Baker’s advice is still sage: Eye injuries in the horse are an emergency and need to be seen by a veterinarian. But unlike the outcome of many eye injuries in 1943, the 2011 message is: Most eye injuries once considered hopeless cases decades ago can heal with appropriate management available.

So why are eye injuries so common in horses?

Evolving as a vision-oriented species, good eyesight and the ability to run helped horses avoid predators. They developed unique features to suit their special visual needs as prey species, grazing animals, and animals dependent on daytime and nighttime vision. The large visual field and improved detection of motion evolved in the horse to help avoid predators.

Horses’ eyes sit on the sides of their heads, giving them tremendous peripheral vision. This anatomical eye position gives horses a total visual field of nearly 360 degrees. Horses can just about see their tails with their heads pointed forward. With a small 65 degrees binocular field of vision, horses use both eyes to view objects within three to four feet, then must turn or lower their heads to continue to observe an object as it approaches.

With extreme lateral placement of their eyes and their "fight or flight" response to threatening movements, horses can be more at risk to eye trauma than other large animals. And corneal ulceration is very common in horses.

So common that one renowned equine ophthalmologist professes: "With eye diseases in horses, there are corneal ulcers ... and everything else!"

The cornea is essentially the "windshield" of the eye and ulceration occurs when various amounts of the cornea are missing. Ulcers can be sight threatening, requiring early clinical diagnosis. There are multiple causes of corneal ulcers including functional, anatomic and traumatic.

Eyelids protect eyes, producing and distributing tear film over them to keep eyes from drying out. Proper shutting is essential, and previous eyelid lacerations can heal abnormally, exposing the cornea to inflammation and ulceration.

Prominence of equine eyes may predispose to traumatic corneal injury in which the outer layer is torn or punctured. Trauma occurs when horses rear, hitting stall ceilings, starting gates or trailer roofs. Ropes, boards, dirt, thorns, twitches, stickers, rasps, wheat beards and nails can all find their way to horses’ eyes. Plant material, trapped under an eyelid, will ulcerate the cornea. Ulcers range from simple superficial breaks or abrasions to full thickness tears.

Horses’ eyes are constantly exposed to bacteria and fungi. Defects in corneas allow organisms to adhere. Infection is a major concern for even the slightest corneal ulcerations. Compared with other species, pathogens attacking the equine eye are some of the strongest and most complicated.

The pathogens aren’t necessarily powerful because of the infections they cause, but the horse’s specific white blood cell response creates serious problems. Severe infections produce ‘corneal melting’ when enzymes destroy structures in the ulcer as it tries to heal.

One centimeter ulcers can heal in approximately six days, but if they become infected, healing can take several weeks or longer. While most corneal ulcers in the horse heal well in a week’s time with appropriate medical therapy, they are not to be underestimated in the horse. Superficial scratches can worsen quickly and progress into something deeper, penetrating the cornea and threatening vision. Deep ulcers and corneal abscesses need immediate attention as the eye risks corneal rupture.

While the cornea is dealing with its own issues of infection and destruction, inflammation of the inner structures such as the uvea can occur secondarily. Uveitis potentially exists in all horses with corneal ulcers and must be treated to prevent further damage.

Corneal ulcers are painful and many horses become reluctant to have their eyes or faces touched. They cannot always see what is touching their painful eye. Lid swelling, eyelid closure, squinting, spasm and discharge from corner of eye occur. Eyeballs suddenly turning cloudy or developing white, yellow or bluish areas suggest corneal disease in horses.

In the early stages, a sign of a painful eye is an eyelash pointing downwards. Normally, horses’ upper eyelashes are almost perpendicular to the corneal surface, but will point downward when painful. Opposite eyes are used for comparison. If one side of the face has horizontal eyelashes and the opposite eyelashes are at half-mast, this is often the sign of an eye problem.

Differentiating between a slightly irritated equine eye and a sore eye requiring immediate veterinary attention is important. If one or both eyes drain yet are wide open, a major injury is unlikely. Wind, dirt, plugged tear ducts and plant reactions can be culprits.

But horses with cloudy, red, painful or injured eyes need urgent veterinary examination for evaluation of corneal and other inflammatory diseases. To facilitate the best repair, eyelid lacerations should be seen the same day. Sedation and topical and regional anesthesia help visualize painful eyes more readily and remove foreign material if present.

A simple and common stall side procedure done by veterinarians uses fluorescein dye that confirms corneal ulcers. Dye colors exposed cornea but does not stain normal, non-ulcerated cornea. All red or painful eyes must be stained as some subtle corneal defects and ulcers are frequently not clearly visible. Cultures are warranted with slowly progressing, non-healing, deep or melting ulcers.

"On account of the delicate structure of the eye, the animal owner will do well to consult with a veterinarian before home doctoring is attempted," – E.T. Baker, DVM, 1943.

What’s going on with the eye determines treatment of corneal ulcers. Goals of medical treatment are preventing or stopping infection, minimizing inflammation, relieving pain and encouraging healing. Medical therapy based on the injury is the first line of defense in ulcer control with treatments every two to eight hours. Ulcers should be treated regardless of size or depth. Deep penetrating ulcers require aggressive and longer therapy. Sugar has no place in current treatment protocols!

Broad spectrum topical antibiotics halt bacterial growth in ulcers. Neomycin/polymixin/neosporin ophthalmic ointment without steroids is commonly used. Antifungal treatment kills fungus, which can be more difficult to treat. Rarely, long lasting eye medications are injected under eyelids in fractious horses that would be unfeasible to treat otherwise. With severe cases, anti-melting therapy can be administered frequently to eyes.

Treating uveitis prevents damage within the eye. Topical atropine minimizes ocular pain from spasm and reduces chances of disruption of structures within the eye. Systemic non-steroidal anti-inflammatory drugs such as Phenylbutazone or Banamine reduce ocular inflammation and treat pain while corneas heal.

Steroids interfere with the immune system of the eye and should not be used in equine corneal ulcers. Although topical steroids have been used in the past to reduce scarring, they could be disastrous if organisms remain in the ulcer.

Corneal ulcers hurt! Treating painful, head-shy horses isn’t easy. Eye irrigation systems are available for safety and treatment compliance. Tubing placed under the eyelid goes to a port that’s braided into the mane where drops are injected. Small discs that fit on the tubing that pump medication are available for cases needing constant treatment or scared young horses. Fly or hard cupped masks protect horses from rubbing their eyes.

Veterinarians can judiciously suture equine eyelids shut temporarily, supporting and protecting eyes. The disadvantage is inability to see the eye daily. Tissue grafts providing corneal support, enhancing healing and preventing rupture are used on deep ulcers and penetrating injuries. Many of these procedures are available in local practices.

Corneal ulceration might initially appear mild and unimportant, but serious and permanent complications can lead to corneal scarring, blindness or eye rupture. Removal of an eye is at times necessary but many saddle horses adapt well to blindness in one eye.

The horse eye has very powerful ocular healing capabilities but may need considerable help to speed the process. Equine veterinary ophthalmologists are finding new ways to treat corneal ulcers so we have fewer blind horses. A horse’s eye wants to heal. Veterinarians’ objectives are to learn how to help it heal.

In 1943, Baker had warm boric acid and mercuric oxides salve in his arsenal of eye medications. He admonished "Do not throw salt the eye, as this is not only painful, but may cause a mean animal."

But in 2011, veterinarians have immense understanding of corneal injuries and the availability of superior treatments. When injuries occur and are recognized and treated as emergencies, is there a chance for good healing? Yes ... The equine "eye"’ definitely has it. — Ginger Elliott, WLJ Correspondent

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