What is a distichia (rarely spelled as dystichia)?

A distichia (plural distichiae) is an eyelash that arises from an abnormal location on the eyelid or grows in an abnormal direction. Distichiasis usually emerge along the margin of the eyelid through the duct or opening of the meibomian gland, although they may arise at other locations along the eyelid margins. The condition in which these abnormal eyelashes are found is called distichiasis.

There are usually multiple distichiae, and sometimes more than one arises from each duct. In some cases, there may be an entire row of extra eyelashes. Even though dogs do not have eyelashes on their lower eyelids, distichiae may be found on either the upper or lower eyelid. In most cases, they will be found bilaterally, or on both eyes.

Distichiasis is similar to, but not the same as, ectopic cilia, a condition that also occurs in dogs (for more details on this condition, please see the handout “Ectopic Cilia in Dogs”).

What causes distichiasis?

 “…but the condition is recognized as a hereditary problem in certain breeds of dogs.”

All eyelashes, like all hairs, arise from hair follicles. With distichiasis, the hair follicles develop in abnormal locations, often deep within the meibomian glands. Since the meibomian glands produce lubricants for the eye, their openings are located along the inner margin of the eyelids. As the eyelash grows, it follows the duct of the gland and exits through the gland opening; thus the distichiae will be directed towards the eye (rather than away from the eye as would be normal for an eyelash). The reason why the follicles develop in this abnormal location is not known, but the condition is recognized as a hereditary problem in certain breeds of dogs. Distichiasis is a rare disorder in cats.