In the upper eyelid there are approximately 100 lashes while in the lower one 50. The eyelashes originate from the anterior portion of the lid margin, in front of the tarsal plate (anterior layer), and are on two or three rows. We can find some eyelashes at the level of the caruncle. From the embryological point of view eyelashes and the Meibomian glands differentiate during the second month of gestation, starting from the same germ epithelial cells (1).
Trichiasis: altered orientation of lashes that, even if they emerge physiologically at the level of the anterior layer, are in contact with the ocular surface. Eyelashes with abnormal direction can affect the total upper and/or lower eyelid, or a portion thereof.
Distichiasis: presence of a double row of eyelashes, the first one resulting from the anterior layer while the other one, metaplastic, from the posterior layer (orifices of the Meibomian glands).
Aberrant lashes: metaplastic lashes that originate from the orifices of the Meibomian glands, located in the back layer (Pictures 1).
PICTURES 1-4: by Dr. Carlo Graziani
All malpositions of the eyelashes can cause eye irritation, epiphora, abrasion and / or corneal ulcers with loss of corneal transparency and more or less serious reduction of vision
The malposition of the eyelid margin and abnormal positions of the eyelashes often coexist: inflammatory causes (chronic blepharitis, Stevens-Johnson Syndrome; vernal keratoconjunctivitis), infectious reasons (trachoma: Picture 2; herpes zoster; parasitosis: dermodex folliculorum), autoimmune causes (ocular pemphigoid scar), or iatrogenic causes (resulting from surgeries: lower blepharoplasty, correction of fracture of the orbital floor, enucleation, ectropion correction; they are secondary to trauma by chemical or physical agents) (3) lead to inflammatory processes in the eyelid edge and the bulbs hair contained therein. The post inflammatory healing can induce changes in the normal anatomical structure of eyelid with consequent malposition of the eyelashes (trichiasis).
Distichiasis can be acquired or congenital (1). The acquired form is secondary to inflammatory, infectious, autoimmune or traumatic processes involving the eyelid margin.
The congenital form can be inherited with an autosomal dominant mechanism, but it can also be associated with ptosis, strabismus, congenital heart defects, mandibulofacial dysostosis or congenital lymphoedema (4). It may remain asymptomatic until the age of 4-6 years, when direct eyelashes against the eye surface become stronger, increasing their abrasive action.
The ìetiopathogenesis of aberrant eyelashes is related to the lack of differentiation in the Meibomian gland of epithelial germ cells, that become pilosebaceous units.
The local medical treatment of malposition of the eyelashes, with lubricants in drops, with creams or through the application of therapeutic contact lens, has the only purpose of reducing the irritative symptoms, resulting from the rubbing of the eyelashes against the eye surface.
Numerous surgical procedures have been described for the treatment of malposition of the eyelashes (5). Different techniques are used depending on the extent of such malpositions (Table 1) (6-13). The various procedures related to the two categories ‘destruction’ and/or ‘repositioning’ of eyelashes/follicles, can be used separately or in combination. The ‘repositioning’ techniques, generally used for the entropion correction can sometimes be useful in the treatment of malposition of the eyelashes because the malposition of the eyelid margin and trichiasis often coexist (table 2), while the ‘destruction’ techniques of eyelashes and follicles are used in a specific way for the treatment of malposition of the eyelashes.
Possible intra- and post-operative complications, that should be discussed with the patient, are: bleeding, infection, recurrence, re-intervention, scars and alteration of the normal palpebral profile.
All eyelid malposition, if untreated, can lead to abrasions, corneal leucomas, keratitis and blindness