trichiasis

Trachoma is caused by a bacterial infection of the eye that spreads through contact with the eye and nose secretions of an infected person, most often in places where clean water and sanitation are scarce. A single infection clears. Repeated infection over years scars the inner surface of the upper eyelid, and the scar tissue contracts until the lid turns in on itself. The eyelashes then point at the eye instead of away from it. That is trichiasis: every blink drags the lashes across the cornea, the clear window at the front of the eye.

The damage is cumulative and painful, and left alone it clouds the cornea until sight is lost. It is also correctable. A short operation rotates the eyelid margin back outward so the lashes clear the eye, and the World Health Organization counts that surgery as the S in its SAFE strategy for trachoma, alongside antibiotics, facial cleanliness and environmental improvement. In 2025, 98,829 people received surgery for the advanced stage of the disease. WHO sets its threshold for eliminating trachoma as a public health problem on trichiasis: cases unknown to the health system must be rarer than 0.2 percent, about one adult in 500, among people aged 15 and over.