Double eyelashes are caused by a disorder known as distichiasis. It is a condition in which hair, or eyelashes, may grow from the openings of tiny oil-producing glands in the lids. These glands are called the meibomian glands. Another form of this condition is lymphedema-distichiasis. This disorder not only causes double lashes but is also associated with certain types of health conditions.
Distichiasis is also known as Blatt distichiasis. "Blatt" is the name of an ophthalmologist who was one of the first to describe the condition in 1924. It is a disorder that is extremely rare and that can occur regardless of a person's age, sex or ethnicity. Double eyelashes can be either hereditary or can occur as a result of other conditions, such as blepharoconjunctivitis. This is a chronic swelling of the eyelids and the mucus membrane lining the inner eye.
Lymphedema-distichiasis syndrome is another hereditary form of distichiasis that occurs with the medical condition lymphedema. Lymphedema is a condition that causes swelling in parts of the body as a result of an excessive buildup of fluid. In addition to having double eyelashes and swelling, people with this syndrome may also have certain health conditions or abnormalities. These conditions are often directly associated with the lymphedema portion of lymphedema-distichiasis and may include heart defects, drooping eyelids, spinal cysts, and even Type II diabetes. The late actress Elizabeth Taylor is said to have had double eyelashes because of this condition.
The two rows of eyelashes caused by either type of distichiasis may appear on both the upper and lower lids. In some cases the double eyelashes may only grow from the lower lid, however it is rare for them to ever appear on the upper lid only. Often the abnormal row of eyelashes grows in shorter and thinner than the normal set of lashes, regardless of the lid.
With both types of distichiasis, abnormal lashes may grow out naturally or turn inward toward the eye itself. When they grow inward, the eyelashes may scratch the surface of the eye and cause discomfort or pain. Double eyelashes that irritate the eye may be pulled by an optometrist or ophthalmologist, although they almost always regrow within a few weeks. Electrolysis is a more permanent procedure that uses an electrical current to kill the lash at the root. Cryosurgery is another permanent way to eliminate the second row of lashes and involves using extreme cold to destroy the abnormal lashes.