Eye conditions in the horse are extremely common, unfortunately, with many of them being traumatic in origin. The majority of equine eye or opthalmic conditions are considered emergencies not only due to potential loss of eye sight, but also due to potential secondary complications. Let’s review the most common conditions affecting the horse as well as some not so common situations, as well as discuss treatment options.
In order to know abnormal, we must first know normal anatomy. Vision in the horse is unique and the field of vision is often limited and restricted. It has been noted that a horse, due to eye positioning, cannot see directly 2-3 feet in front of them or behind them. This helps to explain why some horses become spooked at times when people or objects approach. The eyes are positioned on the side of the head and have both an upper, lower and third eyelid, which sweeps across the eye from the inside corner. The eye or globe itself is filled with fluid to maintain pressure and provide nutrients to the internal tissues. It can be viewed almost as a water balloon of sorts. When viewing the eye grossly, we see the white part or sclera which is covered by a transparent membrane or conjunctiva. The conjunctiva can be more pink on the undersides of the eyelids, but in general is clear. The sclera normally has a light pink or even yellow type of coloration to it and often it is common to see various blood vessels positioned about. The cornea is the clear part of the eye located centrally which when looking through this structure, we can see the iris or pupil area. The cornea is normally clear and has to be clear in order for vision to take place. Any coloration or cloudiness to the cornea is considered abnormal. At the top of the iris, we can often see what looks like is a darker lumpy growth, which is the corpora nigrans, and considered a normal structure. If we look through the dilated pupil with special instruments, we can then see the back of the eye which is the fundus, which contains the optic nerve ,the retina as well as several blood vessels. In general, both eyes should be open, minimal to no drainage and no obvious redness or swelling.
Corneal ulcerations are very common in the horse and are essentially a scratch across the cornea. The source of the scratch is often debris, pollen or foreign material picked up from the environment, but can sometimes be associated with trauma due to an external object or kick. When the scratch first occurs, pain is very common as well as squinting, contraction of the pupil due to pain and increased tearing or drainage from the eye. Usually, the owner notes the closed eye with increased tearing as the initial indications that there is a problem. The cornea is tissue paper thin and in these questions, the concern is how deep the scratch penetrates. In most situations, the scratch is superficial and can be managed readily. In other cases, the scratch penetrates deeper and creates concern about tissue integrating and potential rupture of the globe. Scratches or ulcerations can become infected not only with bacteria but also with fungi from the environment. General therapy for superficial ulcers is administration of anti-inflammatory medications to control pain, topical medications to dilate the pupil and relieve pain and topical antibiotics to prevent infection. In those scratches that go deeper, surgery is often employed to help provide a patch of sorts to cover the defect or to encourage healing. One of the biggest concerns with corneal ulcerations is fungal infections which can be very serious. These are not that common in general practice, but can be secondary to deep wounds or bacterial infections.
Here is an image of a simple corneal ulceration in a horse. What we see clinically is not only squinting with increased tearing, but upon evaluation of the eye, we see cloudiness to the cornea itself as well as migration of blood vessels across the surface, attempting to heal the defect. Remember again that the cornea is generally clear and discoloration and intrusion of blood vessels indicates that there is a problem. We often cannot see the defect or scratch grossly, but have to apply stains to the cornea to help highlight the problem.
Here is an image of a horse that developed a superficial corneal ulcer, but quickly became infected with a fungi. As the fungi develops and the ulcer progresses, it moves into a stage of ‘melting’ in which the tissue essentially degrades quickly and almost appears like slime on the surface of the cornea. This is a very serious situation and often results in enucleation or removal of the eye.
Eye Lid Lacerations
Eye lid lacerations are also fairly common in the horse due to running into objects or being kicked by another horse. The upper eyelid seems to be the most common location of injury in my experience and the most common source of injury is bucket hooks or cross ties in the barn. Any time we are dealing with a laceration, we have a golden period of time to repair that defect. In most instances the time period is 6 hours or less. The reason is due to bacterial contamination to the tissue and complications upon closure. The problem with eyelid lacerations is that they often occur overnight and the owner discovers in the morning, which creates a time issue in terms of closure, but also increases the risk for bacterial infection and tissue integrity. Closure of these defects is almost always performed primarily through the use of sutures and close approximation or restoration of normal anatomy is paramount due to the main function of the eyelids to cover and lubricate the eyes. After most wound closures, it is common to have the patients on topical and systemic antibiotics with anti-inflammatory medications as well as making sure the tetanus status is current.
Here is a photo of a young horse with an upper right eyelid laceration which was repaired successfully.
Conjunctivitis is by definition, inflammation of the conjunctiva or clear membrane covering the sclera. In most cases, the clinical signs include swelling of the eye and eyelids, squinting and discharge. When opening the eye, which can be difficult in some cases, we often see a red, irritated and swollen conjunctiva. It resembles ‘pink eye’ in people and pets. The cause of the irritation is generally a virus, bacteria, allergies or just foreign material from the environment such as dust. It can affect one eye or both. In most cases of conjunctivitis, it is common to evaluate the cornea as well to rule out a corneal ulceration as this can change the course of therapy. If there is no corneal ulceration, the standard treatment includes systemic anti-inflammatories, topical antibiotics, topical steroids and dilators if needed. If a corneal ulceration is present, steroids are not utilized due to potential interference with healing and the immune response, which could make a fungal infection more likely.
Here is a picture of conjunctivitis in a horse complicated by other problems.
Equine recurrent uveitis or moonblindness is also unfortunately a common problem in some horses, with paints and Appaloosas being more predominantly affected. What happens in these patients is an immune response or attack of the internal structures of the eye. This attack creates massive amounts of inflammation and pain, resulting in deterioration of tissue and deposition of inflammatory byproducts within the eye. Clinically, the presentation is very similar to other problems with squinting, possible swelling, discharge and pain. Nerve blocks are often employed in order to open the eyelids for further examination. The damage presented is really dependent on the severity of the uveitis and how long it has progressed. Often we will see conjunctivitis, cloudiness of the corneal, corneal ulcerations and blood vessel infiltration. In other cases, we just have evident pain with cloudiness inside of the cornea (flare) with no other evident issues. An examination of the back of the eye is often performed as is an ultrasound exam in order to determine the integrity of the fundic region, looking for debris floating around. The amount of damage can be extensive and result in complete blindness due to cataract formation, glaucoma and tissue deterioration. The condition can be very painful and hard to manage at times with frequent relapses. The exact cause of the condition is immune mediated and in some cases linked with bacterial infections such as leptospirosis or even strangles. Treatment of uveitis is through the use of systemic as well as topical anti-inflammatories, antibiotics as well as in some cases immunosuppressant type medications such as Cyclosporine. The prognosis is guarded with vision loss a reality in many cases. As a side note, we have noted a good response to our Cur-OST® Anti-inflammatory equine supplements in addition to our Immune formulas in these cases. I feel that the combination of these formulas often helps us to manage the inflammation at a much higher level, yielding more complete results in longer cases of remission.
Cancer of the eye is a not so common problem in the horse but seems to be more prevalent in Paints and Appaloosa breeds. The two main types of cancer that we see are melanomas and squamous cell carcinomas. Melanomas often appear as black growths appearing on or around the eye themselves, while squamous cell carcinoma lesions generally appear as a red, irritated ulcer type growth on the third eyelid, upper or lower lid or even on the cornea itself. Treatment of these types of conditions can be tricky and prognosis guarded, especially for squamous cell carcinomas. Surgery is often employed if the growth can be removed. In other cases, lasers have been employed for removal or topical chemotherapies applied. I have found that by approaching the conditions from an inflammation and immune dysfunction standpoint, we can often get better results with longer remissions in these cases. We have to remember that often in cases of cancer, inflammation is an underlying cause of cellular mutation and growth, but immune dysfunction also plays a major role.
Squamous cell lesions are not always presented on the surface of the eye and visually apparent. Here is a case in which the horse had a squamous cell carcinoma which was actually associated with the conjunctiva, but spread to the surrounding tissue and bone, resulting in severe facial swelling. The swelling actually inhibited proper movement of the eyelids, which then led to secondary problems such as ulceration and conjunctivitis, not to mention uveitis.
This is a general overview of ocular conditions that I have found to be most common in the horse. I feel that owners should be informed not only about clinical signs that a problem is evident, but also be exposed to the conditions themselves, as well as prognosis for each condition. Overall, ocular problems in the horse are of high importance and time is of essence often. If you believe there is a problem, call your veterinarian and seek attention.
All our best,
Tom Schell, D.V.M.
Nouvelle Research, Inc.