Trachoma

Abstract

Trachoma, the leading infectious cause of blindness worldwide, is one of several neglected tropical diseases targeted by WHO for elimination by 2030. The disease starts in childhood with repeated episodes of conjunctival Chlamydia trachomatis infection. This infection is associated with recurrent conjunctivitis (active trachoma), which, if left untreated, leads to cicatricial trachoma characterised by scarring of the conjunctiva, and potentially in-turned eyelashes (trachomatous trichiasis) in later life. Trachoma mainly affects the poorest and most rural communities; these populations typically have limited access to water and hygiene facilities. Blinding complications are most common in women who, in many cultures, act as caregivers from a young age for infected children. To eliminate trachoma as a public health problem, programmes implement a package of interventions known as SAFE; namely, surgery to treat trachomatous trichiasis, antibiotic mass drug administration to treat infection, facial cleanliness, and environmental improvement to limit transmission. The SAFE strategy has brought considerable success in the last two decades. As of December, 2024, 21 countries have eliminated the disease, and several others are on track to eliminate it soon. However, persistent and recrudescent active trachoma in some populations might challenge the success of the 2030 global elimination target. In such settings, novel, or more intensive, approaches must be promptly developed, tested, and scaled up to accelerate elimination.

Figure 1. Clinical features of trachoma and the WHO simplified grading system (as amended in 2020).

Note: A normal upper tarsal conjunctiva is shown for comparison as panel (a). Panels (b) to (h) illustrate the clinical features of trachoma along with the WHO simplified grading system as follows: Panel (b) Trachomatous inflammation—follicular (TF), the presence of five or more follicles, each at least 0.5mm in diameter, in the central part of the upper tarsal conjunctiva (equivalent to Zone 2 plus Zone 3 in Figure 4). Panel (c) Trachomatous inflammation—intense (TI), pronounced inflammatory thickening of the upper tarsal conjunctiva that obscures more than half of the deep normal vessels. Panel (d) Trachomatous scarring (TS), the presence of easily visible scarring in the upper tarsal conjunctiva. Panels (e), (f), (g), (h) Trachomatous Trichiasis (TT), at least one eyelash from the upper eyelid touches the eyeball, or evidence of recent epilation of in-turned eyelashes from the upper eyelid. Panel (h) Corneal Opacity (CO), easily visible corneal opacity that is so dense that at least part of the pupil margin is blurred when viewed through the opacity. Panels (i) and (j) show PTT= Postoperative TT (TT after surgery).

Figure 1. Clinical features of trachoma and the WHO simplified grading system (as amended in 2020).

Note: A normal upper tarsal conjunctiva is shown for comparison as panel (a). Panels (b) to (h) illustrate the clinical features of trachoma along with the WHO simplified grading system as follows: Panel (b) Trachomatous inflammation—follicular (TF), the presence of five or more follicles, each at least 0.5mm in diameter, in the central part of the upper tarsal conjunctiva (equivalent to Zone 2 plus Zone 3 in Figure 4). Panel (c) Trachomatous inflammation—intense (TI), pronounced inflammatory thickening of the upper tarsal conjunctiva that obscures more than half of the deep normal vessels. Panel (d) Trachomatous scarring (TS), the presence of easily visible scarring in the upper tarsal conjunctiva. Panels (e), (f), (g), (h) Trachomatous Trichiasis (TT), at least one eyelash from the upper eyelid touches the eyeball, or evidence of recent epilation of in-turned eyelashes from the upper eyelid. Panel (h) Corneal Opacity (CO), easily visible corneal opacity that is so dense that at least part of the pupil margin is blurred when viewed through the opacity. Panels (i) and (j) show PTT= Postoperative TT (TT after surgery).

Figure 2. Life cycle of Chlamydia trachomatis. Adapted from Mabey et al., 2003.

Figure 3. Estimates of the population at risk for trachoma by country (WHO data)

Figure 4. An everted upper eyelid, showing the gradable sections in the Follicles-Papillae-Cicatricae (FPC) and simplified grading systems

Figure 5. Ethiopia Trachoma Elimination Progress.

Adapted from the Trachoma Atlas February 2025, https://www.trachomaatlas.org. The boundaries and names shown, and the designations used on this map do not imply the expression of any opinion whatsoever on the part of the authors, or the institutions with which they are affiliated, concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries