Page 16 - New Mexico Fall 2020
P. 16

 Eye problems are one of the most common health issues found in the horse. While there are entire textbooks devoted to conditions of the equine eye, this article will focus on a few of the most common ones you are likely to encounter as a horse owner or equine professional. Specific attention will be paid to those conditions that present as acute problems that should be treated as emergencies.
The clinical presentation of the conditions that will be discussed can be quite similar. The primary symptom is eye pain; however, this can manifest itself in a handful of ways. Usually
eye pain presents as tearing, holding the eye shut or being reluctant to open the eye in light, swelling of the eyelids, and a very constricted pupil. Additionally, you may notice a cloudy
or blue appearance of the eye. If any of these symptoms are encountered, a phone call to your veterinarian is warranted. Eye pain symptoms are similar to colic symptoms in that all they tell you is that something is amiss with the eye, not specifically what the problem is. Further investigation is required to know what direction treatment needs to take.
The diagnostic process for an abnormal eye is generally the same for any eye pain complaint, just as the diagnostic process is quite similar at the start of any colic case. Typically, your veterinarian will find the darkest stall available or request you bring the horse into the clinic if there is not an appropriately dark location on the farm. Darkness makes evaluation of all of the structures of the eye much easier. Next, sedation may be administered and a local block of the nerves that control the upper eyelid will be performed to facilitate full visualization of the eye. Examination of the deep and superficial structures of the eye will be performed using an ophthalmoscope. A stain will then be placed on
the surface of the eye to determine if a corneal defect is present. This fluorescein stain adheres to the cells in the cornea that have been exposed and will “glow” bright neon green, allowing any defect to be readily visible. Treatment decisions are often made once the eye has been stained, as treatments are vastly different if a corneal defect is present.
The following conditions are among the most common eye problems seen at our clinic:
Ulcerative keratitis, more commonly known as a corneal ulcer, can range in severity from
a slight abrasion of the cornea penetrating
just through the most superficial layer, to a stromal abscess which penetrates to the very deepest layer of corneal tissue. The cornea
itself is the outermost layer of the eyeball. Its primary purpose is to provide a physical barrier to prevent the invasion of pathogens into the eye and to prevent too much fluid uptake into the stroma (middle layer of corneal cells). The cornea is only about as thick as 10 sheets of printer paper stacked together, and the outer layer of cells is as thick as 2 sheets. The cornea has a very poor blood supply, making healing of any defect a more complicated process than an abrasion in a location such as the skin. More diagnostic steps, such as culture and cytology, may be taken in severe cases to better help plan the needed treatment.
Typical corneal ulcer treatment involves the use of ophthalmic grade topical antibiotics, antifungals, or both, along with topical atropine. Systemic anti-inflammatories such as flunixin or firocoxib are often implemented as well. The topical medications may be delivered in the form of an ointment or solution. Most superficial ulcers can be treated with an ointment a few times a day.
More severe cases, however, often require
a more extensive treatment protocol, and therefore may necessitate the use of a sub palpebral lavage system to administer the medication as a constant flow. Adjunctive treatment may also involve the use of serum or medications known as antiproteases to lessen the formation of fibrin within the anterior chamber of the eye. Atropine is used in most all eye pain cases to dilate of the pupil. Pupillary constriction occurs secondary to pain and is itself painful, and prolonged pain and constriction can lead to other ophthalmic conditions. Atropine is a mainstay in the treatment of any ophthalmic case.
Uveitis, or inflammation of the uveal
tract, can occur secondary to even superficial corneal ulcers or may be seen as its own primary acquired eye condition. The uveal tract is composed of the iris, which is readily identifiable as the structure that gives the
eye its color, as well as the ciliary body. The ciliary body is responsible for production of the aqueous humor of the eye and muscular control of the lens. Uveitis often presents
as a blueish or cloudy appearance of the eye (corneal edema), is exquisitely painful, and
will lead to many of the eye pain symptoms listed above with a few other distinctive characteristics of its own. Specifically, it is common to see blood, pus, or fibrin within the anterior chamber of the eye and engorged blood vessels within the sclera. Sometimes, however, the symptoms may be as subtle as the eyelashes of the affected eye pointing down, rather than straight out. Uveitis is the number 1 cause of blindness in the horse and while prevalence of some manifestation of uveitis is thought to be between 8-25% only 1-2% of affected horses have symptoms severe enough to lead to vision impairment.
Common Equine
Eye Abnormalities
by Megan Petty, DVM
 14 New Mexico Horse Breeder












































































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