Equine Eye Problems Get a Closer Look: In Vivo Corneal Confocal Microscopy

A new noninvasive technique, called in vivo corneal confocal microscopy, helps veterinarians locate and identify infections, microscopic foreign objects and other equine eye conditions without biopsy or other surgery.

Your horse’s large, prominent eyes give him a wide field of vision. Unfortunately, their size and placement also make them prone to problems. Injuries and infections in the cornea, the surface layer of the eye and its first line of defense, are common—and when they’re not promptly treated, they can cost the horse his sight.

Eric Ledbetter, DVM, examines a horse’s eye using a corneal confocal microscope, a microscope that can be used on living tissues. | Courtesy, Mike Carroll, Cornell University

Now veterinarians at Cornell University are using a new noninvasive technique to diagnose these problems quickly and safely. Called in vivo corneal confocal microscopy, it helps them locate and identify infections, microscopic foreign objects and other equine eye conditions without biopsy or other surgery. The technique was adapted for veterinary use from human medicine, and Cornell veterinary ophthalmologist Eric Ledbetter, DVM, was the first to apply it to horses. “This is a very new technology and we are actively working to find other applications in equine ophthalmology,” he says.

The corneal confocal microscope is basically a microscope that can be used on living tissues. It uses a beam of laser light to scan the cornea, which is only about 1 millimeter thick in the horse but has several distinct layers. The confocal microscope can focus with pinpoint precision on specific areas in each layer of tissue, screening out stray light and producing crisp, clear images of corneal cells and minute abnormalities.

Those sharp images can save valuable time. For example, horses often get infections of the cornea. Bacterial or fungal? You have to find out what’s causing the infection to treat it. Traditionally, that’s been done by scraping tissue from the cornea and sending it to a lab to be cultured. But culturing takes time—culture results for fungal infections can take 10 to 14 days to come back, Dr. Ledbetter says—and meanwhile the condition may go untreated or be treated incorrectly.

By contrast, in vivo corneal confocal microscopy can identify these infections on the spot. Telltale structures of fungi and yeast show up as clearly in the living eye as they do in laboratory specimens, even in the deepest layers of the horse’s cornea. Dr. Ledbetter has also used in vivo corneal confocal microscopy to identify tumors, scratches and other eye problems.

In a paper published earlier this year in the journal Veterinary Ophthalmology, he showed how the technique can quickly identify microscopic foreign objects like burdock and other plant fragments that become embedded in horses’ eyes. To validate the results, he compared his images to results from traditional biopsies. Showing that the findings match, he says, “paves the way for veterinarians to definitively diagnose eye diseases in horses with only this new technology, minimizing impact on the eye and saving time to get patients treatment faster.”

This article was originally published in the May 2014 issue of Practical Horseman.

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