Overall objective

• To evaluate the reliability of the trachomatous scarring (TS) examination data collected from trichiasis (TT) cases in surveys and determine the potential impact of different levels of agreement on the burden of TT

Specific objectives

•  To estimate the proportion of TT cases identified during surveys in trachoma endemic regions who were originally recorded as having ‘no trachomatous scarring’ that actually have a degree of conjunctival scarring, on expert re-grading
•  To compare the phenotype of TT cases with and without TS and their relationship to vision in trachoma endemic settings
•  To identify factors associated with scarring among TT cases in trachoma endemic settings
•  To estimate the potential impact on the global burden of different levels of agreement between the survey grading and independent expert grading, if TS is considered in the diagnosis

This cross-country study in Ethiopia, Uganda and Nigeria will examine the validity and reliability of TS data associated with TT cases from prevalence surveys undertaken in high and low burden settings. The TS ‘survey’ data from 400 TT cases will be compared with an independent expert re-assessment (masked to TS ‘survey’ status) and grading of high-resolution digital photographs of the tarsal conjunctiva to estimate:

• the survey TS false negative rate
• the sensitivity, specificity and positive predictive value of the initial (and independent) survey grading compared to the photograph grading.

To reduce any systematic bias in photograph grading the set of photos for grading will include an additional 100 people (frequency matched by age, sex, and location to quarter of the TT cases) from the original survey without TT.

The study will also investigate the relationship between:

• the degree of conjunctival scarring (determined by the photograph grading) and the nature (entropion, metaplastic, misdirected) and severity of the TT (numbers of lashes)
• the degree of visual impairment and the type and severity of trichiasis, with respect to the degree of scarring.

The results of the study will contribute to ongoing debate over whether the definition of TT for the purpose of defining prevalence targets for elimination as a public health problem, should be revised to include a specific reference to and dependency on the presence of TS.