Distichiasis is a congenital or acquired condition in which there is an accessory row of eyelash cilia behind the normal row. The disorder may be familial with an autosomal dominant pattern of inheritance, but may also follow severe inflammatory or traumatic injury. It is believed that these abnormal lashes develop as a result of metadifferentiation of primary epithelial germ cells originally intent upon meibomian gland development. The meibomian glands are modified sebaceous glands that are not associated with the eyelashes or other hairs. In the skin sebaceous glands are usually associated with a hair follicle and an apocrine sweat gland to form a pilosebaceous unit. Under some circumstances it is believed that the meibomian gland can undergo differentiation into a primitive pilosebaceous unit producing an abnormal distichitic eyelash.
CLINICAL CHARACTERISTICS The eyelid margin is typically normal with respect to the globe and the normal eyelashes are oriented appropriately. Extra, often very fine cilia are seen arising in association with the meibomian gland orifices. These abnormal lashes are directed backward toward the corneal surface where they produce ocular surface symptoms of foreign body sensation, conjunctival injection, corneal abrasion, and reflex epiphora. Distichiasis can be focal with only a few abnormal lashes, or diffuse where they can extend across the entire eyelid margin.
TREATMENT Mechanical epilation of the offending distichitic lashes will provide temporary relief of symptoms, but the cilia will usually re-grow within three to four weeks. For a permanent cure ablation of the lash follicles is required. Electrolysis, radiosurgery, or cryosurgery are all equally effective. However, unlike trichitic lashes, in distichiasis the cilium shaft may run a circuitous course from the bulb to the lid surface making destruction with an epilating needle more unpredictable. Internal lash resection beneath a skin muscle flap or using a lid-splitting technique is effective, but because the bulbs lie within the tarsus, finding them can be difficult.
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