Distichiasis is a congenital or acquired condition in which there is an accessory row of cilia behind the normal row of eyelash cilia. This disorder may be familial in origin with an autosomal dominant inheritance, but may also be produced by acquired conditions such as severe inflammation or trauma. It is presumed to be due to differentiation of primary epithelial germ cells originally destined for development of meibomian or tarsal glands. Meibomian glands are modified sebaceous glands located in the tarsal plate of eyelids. In skin, pilo-sebaceous unit consists of sebaceous glands associated with hair follicle and sweat gland. It is believed that meibomian gland may undergo differentiation into primitive pilo-sebaceous unit which produces distichiasis.
The roots of eyelashes (cilias) lie against the anterior surface of the tarsal plate. The cilia come out of skin at the anterior lid margin and curve away from the globe. The lid margin from anterior to posterior comprises of
Distichiasis may present only a few isolated eyelashes, or as a complete accessory second row of lashes. These lashes often rub against the cornea and produce irritation of eyes. Unlike distichiasis, occasionally there may be tristichiasis (three rows of cilia) or tetrastichiasis (four rows of cilia).
Symptoms of distichiasis may include
Distichiasis may be congenital or acquired.
Congenital distichiasis: Congenital distichiasis is almost always associated with lymphoedema distichiasis syndrome (LDS), an autosomal dominant condition that is characterised by two parallel rows of cilia at the eyelid margin and lymphoedema of the extremities. Lymphoedema may present after the age of ten years and may not be noticeable at the time of presentation of distichiasis. Associated abnormalities include entropion, ptosis, cleft lip and palate, webbed neck, vertebral anomalies, and congenital heart defects. Isolated congenital distichiasis is extremely rare.
Acquired distichiasis: Acquired distichiasis is more common than the congenital form. It is seen more often with chronic inflammatory conditions such as blepharitis, staphylococcal hypersensitivity, meibomian gland dysfunction (MGD), chemical injuries to the eyes, Stevens-Johnson syndrome, and ocular cicatricial pemphigoid.
Diagnosis depends upon slit-lamp examination by an eye-specialist.
Congenital distichiasis: Examination shows eyelashes exiting posterior to the normal row of lashes. These lashes emerge at or slightly behind the meibomian gland orifices. The aberrant lashes tend to be thinner and shorter than the normal lashes and are often directed posteriorly. These cilia are usually well tolerated during infancy and may not be symptomatic until five years of age.
Acquired distichiasis: Since it is caused by metaplasia of the meibomian glands into hair follicles, variable number of lashes grows from meibomian gland openings. In contrast to congenital distichiasis, the lashes tend to be non-pigmented and stunted, and are usually symptomatic.
Distichiasis may be associated with signs of conjunctival redness and chemosis, epithelial breakdown of cornea, corneal scarring or pannus formation.
Differential diagnosis of distichiasis includes conditions like
Management should be carried out under medical supervision.
Patients without symptoms or keratopathy do not require any treatment.
Various surgical procedures may be used for the treatment of distichiasis.
Prognosis is good if prompt treatment is initiated before permanent damage to the cornea.
Recurrence of distichiatic cilia after surgical intervention may still take place.
Untreated distichiasis may lead to complications like
Acquired distichiasis may be delayed by proper treatment of diseases such as blepharitis, and ocular cicatricial pemphigoid.