Managing the blue eye blues: Equine corneal disease - DVM
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Managing the blue eye blues: Equine corneal disease
Corneal disease and damage resulting in cloudy, blue eyes has many causes.


DVM360 MAGAZINE


Treatment


Photo 4: This horse showed a case of severe diffuse corneal edema but without any signs of trauma or pain.
Treatment for a blue or cloudy eye should be aggressive and started immediately. Staining the eye surface with a fluorescent dye and rose bengal dye is generally the first step in diagnosing corneal damage. The normal cornea is impermeable to dust, debris and stains. If some damage to this outer layer has occurred, then dye will adhere to the defect, making it easily visible. When corneal scratches or abrasions are detected, topical antibiotics, along with antifungal agents and anti-inflammatory medications, are applied frequently (four to six times daily) to the eye surface.


Photo 5: The same horse as in Photo 4 after months of treatment. The corneal edema is beginning to clear at the corner of the eye.
If uveitis is suspected, then nonsteroidal anti-inflammatory medications will be used both systemically and topically. Atropine or other drugs designed to dilate the pupil, promote drainage of ocular fluid and reduce ocular pain are also commonly used. Additional systemic drugs used to lower intraocular pressure (e.g., mannitol) may be indicated in suspected glaucoma cases. Monitoring the degree and extent of bluing to the cornea, as well as the level of pain and irritation, may give an indication of healing and recovery, though corneal edema in some cases can take a long time (months) to resolve (Photos 4 & 5).

Immune-mediated keratitis

The one common thread in almost all cases of a blue eye in horses is that these animals are in pain and uncomfortable. This is exactly why these cases are difficult to miss. An agitated horse with a squinty, closed, tearing, cloudy eye that stands in its stall rubbing its face on everything is hard to overlook. The pain from glaucoma, uveitis or corneal abrasions is very evident.

Much more confusing, however, are those rare cases in which a horse will acutely develop a blue eye without any trauma or history of problems and with virtually no clinical signs. These horses are often fine when turned out but return with a blue eye. They are normal in all other aspects and have no swelling, tearing or any evidence of ocular pain. They do not typically take up dye when their eye is stained, and the results of an ocular ultrasonographic examination is normal. They are functionally blind because of the extreme amount of corneal edema and tend to show multiple punctuate nonulcerative lesions to the cornea (small indentations or dimples covered by normal corneal tissue).

It is now thought that a large proportion of these horses may be affected with immune-mediated keratitis (IMMK). IMMK is problematic worldwide, and this disease was discussed at the recent Equine Ophthalmology Consortium in Vienna, Austria. Susan Keil, DVM, MS, Dipl. ACVO, attended this conference and says, "IMMK is likely more than one disease lumped together under one name, and its cause and pathophysiology are not yet understood."

Horses with IMMK show corneal edema and a very blue eye, but the damage to the cornea does not resemble fungal or bacterial eye disease. Brian Gilger, DVM, MS, Dipl. ACVO, Dipl. ABT; Tammy Michau, DVM, Dipl. ACVO; and Jacklyn Salmon, BS, of the Department of Clinical Sciences, College of Veterinary Medicine at North Carolina State University recently reviewed a number of cases of IMMK and concluded that, "in all cases of IMMK, signs of uveitis or severe discomfort were not observed."

While true IMMK cases are still uncommon, this disease should be considered when encountering a horse with a blue eye, especially if that horse is not in pain. If pain is an important part of the presentation, then swift and aggressive treatment should be sought. Assessing for corneal abrasions or damage, glaucoma and uveitis will cover most of these types of eye cases. Appropriate treatment should be initiated quickly, and, in most instances, positive outcomes for horses with blue eyes can be achieved.

Dr. Marcella is an equine practitioner in Canton, Ga.


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Source: DVM360 MAGAZINE,
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