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Trachoma remains the world's leading infectious cause of blindness.1 Trachoma control programmes determine when to start and stop mass antibiotic treatments based on the prevalence of follicular trachoma (TF) in children aged 1–9 years, as assessed by examination of the upper tarsal conjunctiva using the WHO simplified grading system.2 According to the WHO classification, TF is defined as the presence of ≥5 follicles at least 0.5 mm in diameter. The original paper describing the WHO simplified grading system included a diagram of the everted conjunctiva with examples of follicles that were 0.5 mm in diameter.2 However, in our clinical experience, the follicles in this diagram seem to be less than 0.5 mm when considered relative to the size of the conjunctiva. In this article, we measured the size of the follicles on the WHO diagram relative to photographs of everted conjunctivae from clinical trials in Niger and Ethiopia in order to determine whether the follicles in the diagram meet the WHO threshold of 0.5 mm.
Trained photographers used Nikon D-series digital SLR cameras with Micro-Nikkor 105 mm f/2.8 lenses …