Distichiasis is a rare ocular pathology characterized by aberrant growth of an accessory row of eyelashes from the posterior lamella of tarsal plate, the epithelial germ cells of which normally contain meibomian glands but are abnormally differentiated into pilosebaceous unit.
Distichiasis has been observed in 94% individuals if present at birth and 75% of those present with ocular findings such as irritation of cornea, intermittent conjunctivitis, photophobia and ptosis. As described earlier, it is easy to identify and differentiate the two varieties of distichiasis based on physical appearance of aberrant eyelashes, previous history and presence or absence of underlying ocular illnesses. Typically, a slit lamp is used to examine the eye and corneal epithelium. The lamp is instilled with fluorescein dye to observe and evaluate ocular defects and abnormalities.
In acquired distichiasis, the lower eyelids are typically affected but the form and appearance of the accessory eyelashes can vary widely in different cases, from being full and heavy to very fine and light, highly pigmented and dark to very lightly pigmented or nonpigmented and adequately aligned and oriented to irregular alignment and misdirected growth. The acquired form, as mentioned before, develops as a results of chronic ocular inflammatory conditions.
In lymphodemea-distichiasis syndrome (LD), the ocular condition persists since childhood although lymphedema develops in later years or after puberty. Therefore, children suffering from distichiasis must be evaluated for possibility of development of lyphedema and a complete family history must be taken.
It is imperative to gather a complete family history on identifying any case of distichiasis. To rule out the presence of lymphedema-distichiasis syndrome, patient's history should include asking about any signs of lymphedema that may have appeared and the patient should be counseled about possibility of development of lymphedema in lower limbs. In cases when children are diagnosed with distichiasis during early childhood, the child's parents must be counseled about lymphedema and associated genetic anomalies such as cleft palate and congenital heart disease that may ensue. Lymphedema is clinically diagnosed by lymphoscintigraphy. Presence of false negative results should be kept in mind when making diagnosis on confirmatory investigation. In some cases, genetic investigation up to the molecular level is required to spot mutations in FOXC2, an important transcription factor that plays a vital role in several developmental pathways.
There is no specific treatment for all cases of distichiasis. Several treatment options are available and choice of treatment depends upon number of aberrant eyelashes (full or few), patient's age, presence of other comorbidities and patient's personal preference.
For temporary symptomatic relief, lubrication therapy or epilation are employed. In lubrication therapy, an eye ointment is applied on the ocular surface to prevent abrasion of corneal epithelium and to reduce discomfort and irritation. The method, however, is not patient compliant as it cannot be used during working hours.
Epilation of the misdirected row of eyelashes is also employed to provide temporary relief. The misdirected eyelashes are isolated and removed completely from the root of hair shaft using forceps. It is highly important that the root of each hair follicle emerges out intact because any hair follicle removed incorrectly (broken along the hair shaft and not removed from the base) causes more irritation to the patient. The method is temporary as the aberrant eyelashes typically regrow within 2-3 weeks after epilation  .
Procedures for removing the misdirected eyelashes permanently include cryotherapy, direct surgical excision of eyelashes by wedge resection , electrolysis, argon laser ablation, diode laser and trephination. Maintenance of aseptic, sterile environment during performance of any of these procedures and use of antibiotics prophylactically are highly important to minimize the chances of infection.
In cases when the aberrant eyelash cilia are fewer in number, electrolysis or argon laser ablation may be used. In electrolysis, topical anesthetics or general anesthesia may be required in aged and debiliated patients but the chances of recurrence are high and the eyelashes may regenerate even after the procedure. In argon laser ablation, the hair shaft of patient's accessory set of eyelashes is exposed to slit lamp equipped with argon laser. Typically, argon laser with a power of 1000-1500 mW and spot size of 50-100 µm are exposed for a duration of 0.1-0.2 seconds with provision of 12-30 laser shots to each eyelash. Depending on patient's condition, topical or local anesthetics may be required during this procedure. With argon laser ablation, chances of recurrence may vary from 12%-41%.
Cryotherapy is another procedure for a more permanent treatment of distichiasis with a success rate of 95%. In this method, nitrous oxide or carbon dioxide are used as cryogen and hair follicles of misdirected eye lashes are permanently destroyed by freezing them to a temperature of -20°C. Cryotherapy is more preferred to be used twice as double free-thaw application technique provides more effective treatment of the the misdirected eyelashes.
Another effective procedure for treating distichiasis is the use of diode laser. In this method, 810nm diode laser with pulse length of 50ms and energy intensity of approximately 50 J/cm2 is used to treat abnormal eyelashes. The treatment is needed 4-5 times with 4-6 weeks apart to provide most effective results .
A much safer, faster alternative treatment with lesser chances of complications is trephination. In this technique, sisler ophthalamic microtrephine (1.0mm) is used to cut eyelash hair follices .
Surgical methods of treatment carry risk of post surgical complications which comprise hemorrhage, infection, wound dehiscence, eyelash regrowth, entropion or ectropion. Use of antibiotics and adequate electrocautery can reduce the chances of infection and hemorrhage respectively.
Distichiasis can be acquired or congenital. The two different forms of the disease possess different etiologies. Acquired distichiasis occurs due to metaplasia of meibomian glands into pilosebaceous glands which results in the formation of an accessory row of eye lashes. The aberrancy can develop due to chronic inflammatory conditions of eyes such as blepharitis or conjunctivitis, eye injuries or Stevens-Johnson syndrome.
The congenital form results from aberrant differentiation of meibomian glands into hair follicles during development. Congential distichiasis is autosomal dominant with complete penetration  .
Distichiasis develops rarely and has been reported in individuals belonging to all ethnic classes, in all age groups and equally in both male and female gender.
The two forms of distichiasis are easily identified and differentiated. As described earlier, congenital distichiasis is a developmental condition. The disease is not presented clinically before 5 years of age as the accessory eyelashes are fine during infancy and do not cause ocular irritation. In acquired distichiasis, on the other hand, which results from a chronic inflammatory condition of the eyes, the accessory eyelashes are fine and nonpigmented and cause consistent ocular irritation.
It is highly important to differentiate distichiasis from other apparently similar ocular illnesses. Eyelids must be examined physically for appropriate evaluation to make the correct diagnosis. The ocular conditions that must be ruled out to prevent misdiagnosis of distichiasis are trichiasis, in which the eyelashes are formed in the anteror lamella, entropion, epiblepharon which frequently occurs in children, lid scar, blepharoconjuctivitis and cicaticial conjunctivitis.
Congenital distichiasis cannot be prevented nor can be acquired distichiasis. However, it is possible to reduce the extent of edema in ymphedema-distichiasis (LD) syndrome by application of hosiery prior to the development of lymphedema. Secondary complications can be prevented by prompt treatment of any infection with antibiotics.
Distichiasis refers to a condition of eyelids that arises when primary epithelial germ cells, instead of differentiating into meibomian glands, aberrantly differentiate into pilosebaceous glands on the posterior portion of lid margin which results in the formation of an extra, abnormal row of eye lashes. The accessory eye lashes formed can either be fine and slightly pigmented or coarse and equally pigmented as normal eyelashes. This second inner row of eyelashes, because of being in close proximity to cornea, can cause corneal irritation which can lead to corneal scarring, epiphora, astigmatism and keratoconus . Other ocular conditions that have been reported to be associated with distichiasis comprise corneal hypoesthesia , photophobia, ptosis, congenital cataracts, congenital ectropion, congenital entropion, extropia , absent lacrimal duct , epicanthus, telecanthus, eyelid edema, color blindness , microphthalmos, dystrophic retinal pigmentation and optic disc pallor as in the oculo-cerebro-renal syndrome .
Distichiasis is either identified as acquired or as congenital. Acquired distichiasis has been found to occur in certain chronic inflammatory conditions, following chemical injuries of eyelids, and in conditions like Stevens-Johnson syndrome and ocular pemphigoid. Acquired distichiasis has usually been observed in the lower eyelids but the accessory lashes formed can be full or fine, pigmented or nonpigmented, aligned or misaligned. Congenital distichiasis results from abnormal development of an accessory row of eyelashes before birth with complete penetration. The defect results from failure of the basal epithelial cells to differentiate into meibomian glands during development. Congenital distichiasis may sometimes accompany ptosis, madibulofacial dystosis, or stabismus.
Distichiasis is also associated to be present in an autosomal dominant disorder, lymphodema-distichiasis (LD) syndrome, which is characterized by presence of lymphedema of lower limbs and formation of aberrant eyelashes on the posterior margin of eyelids  .
Normal eyelids contain single rows of eyelashes. The inner, posterior portion of eyelids that is close to the eyeball contains glands which produce an oily substance that becomes part of tear film. In some conditions, these glands are replaced by another accessory row of eyelashes. This condition is referred to distichiasis. The accessory eyelashes can be formed on any of the four or all four eyelids and can be fine and slightly pigmented or full and darkly pigmented. Formation of accessory eyelashes on the posterior portion of eyelid causes irritation of eyeball and in the long term, damage to its structure.
There are two types of distichiais that are identified, congenital distichiasis and acquired distichiasis. Congenital distichiasis is typically present since childhood and is mostly found to be associated with lymphedema-distichiasis (LD) syndrome. In LD syndrome, accessory rows of eyelashes are present along with lymphedema, which is swelling of lower limbs. Acquired form of the disease is usually developed later in life, often as a result of eye injuries or inflammation.
Distichiasis is characterized by the presence of irritation of eyeballs and visible presence of accessory set of eyelashes. It is easily identified and in case of children, a complete family history is needed to detect chances of development of LD syndrome. Parents should be counseled about regular follow ups and preventive measures that should be taken in order to avoid problems that appear later with development of lymphedema.
Several treatment options are available to treat distichiasis. Eye ointments can be used to soothe irritation by lubricating the eyeball. Epilation of accessory eyelashes by removing each lash from the hair shaft using forceps provides temporary ease and comfort but the eyelashes regenerate within 4 weeks.
Permanent methods for treating the disease are electrolysis, cryotherapy, trephination and laser. The choice of treatment depends on number of accessory eyelashes (fewer or more) and patient's health condition. Cryotherapy is one the most effective and permanent surgical options available with a success rate of 95%.