Introduction A survey to determine the prevalence of trachomatous trichiasis (TT) requires a large sample size and the recommended participant age is ≥15 years. This study sought to establish the appropriate age range of individuals to be included in TT surveys.

Methods Data from six previous surveys of adults ≥15 years old were reanalysed.

Results Reanalysis indicated that 69.6–93.3% (average 87.0%) of untreated TT occurred in those aged 40+ years and 52.2–86.7% (average 73.1%) in those aged 50+ years (age ≥50 years is used in rapid assessment of avoidable blindness). Age ≥40 years was adopted in a TT survey conducted in Turkana district because it allowed a smaller sample size than age ≥15 years.

Conclusions The estimated backlog of untreated TT in people aged ≥40 years old in Turkana was 5932 and the overall TT backlog was likely to be 6358–8523. These findings cannot be generalised because all surveys were carried out in the same country.