Uniquely colored equine coats can be both eye-catching and eye disorder-causing. Take horses with the silver-coat mutant gene, for instance: Many suffer from multiple congenital ocular anomalies (MCOA), or eye issues that can cause, among other things, a bulbous bulging of the eye. Recently, a group of French scientists took a deeper look into affected horses' eyes, and their looking glass of choice was the ultrasound machine.

The silver dapple coat—which isn’t technically a “dapple,” but rather a dilution caused by a genetic mutation that produces a dark body color with a flaxen mane and tail—is common in certain breeds, including the Rocky Mountain Horse and the Icelandic horse. One breed with a very strong silver gene representation is the French Comtois draft horse, which has been selectively bred for centuries to favor coat color, said Jean-Luc Cadoré, DV, PhD, Dipl. ECVIM, professor of internal medicine at VetAgro Sup at the University of Lyon in France.

In the past few years, researchers have pinpointed the gene–PMEL17–responsible for both the silver coloring and the eye disorders. In their study, Cadoré and his colleagues investigated the eyes of Comtois horses and Rocky Mountain Horses carrying at least one copy of the allele and compared their results to horses of the same breeds without the PMEL17 gene. They evaluated the eyes of 85 horses (including 10 control horses without the mutation) using both a direct ophthalmoscope (a hand-held ophthalmoscope that human ophthalmologists use in clinical settings) and ultrasound.

They found that ultrasound was a practical, fast, and easy-to-use tool for investigating the possible disorders caused by a PMEL17 mutation, Cadoré said. In fact, for many pathologies—including ciliary cysts (fluid-filled cysts of the eye's ciliary body) —ultrasound was far more powerful than direct ophthalmoscopy in finding instances of disease