Trichiasis

Trichiasis is an acquired condition where one or more eyelashes, although arising from their normal anatomic position at the lid margin, are misdirected posteriorly toward the cornea and ocular surface, causing chronic mechanical irritation. The term must be distinguished from related conditions: distichiasis (accessory row of lashes emerging from meibomian gland orifices), entropion (inversion of entire eyelid margin causing all lashes to contact globe), and metaplastic eyelashes (lashes arising from abnormal locations following inflammation or surgery).

Epidemiology and global burden: Trichiasis affects approximately 1-3 percent of the adult population in developed countries with significantly higher prevalence in elderly (5-10 percent over age 70). Globally, trachoma-related trichiasis affects 2-3 million individuals, predominantly in trachoma-endemic regions of sub-Saharan Africa, Middle East, parts of Asia, Central and South America, and Indigenous populations of Australia. Trachomatous trichiasis is the leading infectious cause of preventable blindness worldwide and a key target of WHO's GET 2020 (Global Elimination of Trachoma) and ongoing 2030 elimination programs through SAFE strategy (Surgery, Antibiotics, Facial cleanliness, Environmental improvement).

Etiology and pathophysiology: 1) Chronic blepharitis — most common cause in developed countries; recurrent inflammation of lid margin with associated meibomian gland dysfunction causes localized scarring of the lash follicles, distorting their direction; 2) Trachoma sequelae — repeated infection with Chlamydia trachomatis serotypes A, B, Ba, C in childhood causes follicular conjunctivitis (TF), intense inflammation (TI), and progressive conjunctival scarring (TS) on the upper tarsus, ultimately leading to entropion-trichiasis (TT) in adulthood and corneal opacity (CO); 3) Ocular cicatricial pemphigoid — autoimmune subepithelial bullous disease with autoantibodies against laminin-332 (epiligrin) and BP180; chronic conjunctival inflammation with progressive symblepharon (conjunctival adhesions) and forniceal foreshortening; 4) Stevens-Johnson syndrome and toxic epidermal necrolysis sequelae — severe drug or infection-related mucocutaneous reaction with chronic ocular surface scarring; 5) Chemical or thermal burns — alkali burns (lime, ammonia) cause severe ocular surface scarring; 6) Herpes zoster ophthalmicus — reactivation of varicella-zoster virus in V1 distribution causes lid scarring; 7) Chronic graft-versus-host disease — post-transplant chronic inflammation; 8) Vernal and atopic keratoconjunctivitis — chronic allergic inflammation; 9) Surgical or traumatic eyelid scarring; 10) Congenital distichiasis (rare autosomal dominant — FOXC2 mutations associated with lymphedema-distichiasis syndrome).

Symptoms and complications: Symptoms include foreign body sensation (most common — like an eyelash in the eye that cannot be removed), photophobia, reflex tearing (epiphora), conjunctival redness, blurred vision, and pain. Complications include: 1) Punctate epithelial keratopathy (mild surface epithelial defects from mechanical abrasion); 2) Corneal abrasion (acute traumatic defect); 3) Recurrent corneal erosion; 4) Microbial keratitis (secondary infection of compromised epithelium — bacterial, fungal, acanthamoeba); 5) Corneal neovascularization (chronic inflammation drives ingrowth of new blood vessels); 6) Corneal scarring and opacification (with permanent vision loss if visual axis affected); 7) Corneal ulceration with risk of perforation; 8) Sterile inflammatory infiltrates; 9) Significant impairment of vision-related quality of life and ocular surface comfort.