Q. Why can I see the whites of my horse’s eyes all the time, even when he’s relaxed? He is a chestnut Appendix Quarter Horse gelding.
—Esmé, Claremont, California
A. The “eye whites” you are describing is the white color of the conjunctiva, third eyelid, and sclera, tissues that surround the central, clear cornea of the eye.
There are several reasons that a horse may have more of this white area showing. The most common reason is simply less pigmentation or brown coloring. Lightly colored horses, such as Paints, Appaloosas, and some chestnut horses have less overall pigment in their skin, including the areas around the eyes. Without the pigment, the white areas are much more visible.
Generally, this lack of pigment has no health or vision affects; however, horses with less pigmentation are more susceptible to developing skin cancer or squamous cell carcinoma. Therefore, I advise that these horses be protected from direct sunlight using fly masks or similar protective devices.
If there’s a sudden or gradual development of increased eye white, this may indicate a problem. A painful eye may have an elevated third eyelid, and an eye that has been damaged might become smaller than normal and show more scleral white. Therefore, if you notice a change in the eye regarding the amount of scleral white, I encourage a thorough examination of the eyes by your veterinarian.