What is Distichiasis ?
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
- Eyelashes.
- Grey line (border between anterior (lash, skin and orbicularis oculi muscle) and posterior (tarsal plate and conjunctiva) lamella.
- Meibomian gland orifices.
- Mucocutaneous junction.
- Conjunctiva.
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).
Distichiasis Symptoms
Symptoms of distichiasis may include
- Decrease of vision.
- Pain in eyes.
- Redness.
- Irritation.
- Foreign body sensation.
- Watering.
- Chemosis.
- Corneal scarring.
- Corneal ulcer.
Distichiasis Causes
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.
Distichiasis Diagnosis
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
- Trichiasis: Trichiasis is a condition in which eyelashes from the normal anterior margin are misdirected towards the eye.
- Entropion: Entropion is a condition in which the entire eyelid margin turns inward.
- Epiblepharon: Epiblepharon is a condition which is seen mostly in children. Here the lashes are not truly misdirected, but are pushed back by the fold of skin against the globe.
- Chronic blepharoconjunctivitis.
- Cicatricial conjunctivitis.
Distichiasis Complications
Untreated distichiasis may lead to complications like
- Corneal scarring.
- Thinning of cornea.
- Corneal ulcer.
Distichiasis Prevention
Acquired distichiasis may be delayed by proper treatment of diseases such as blepharitis, and ocular cicatricial pemphigoid.