Sampling procedure
The sampling framework employed for the study was based on the number and demography of the children enrolled in nine schools with an SFP in Zanzibar. We estimated that about 6000 children from the school register were enrolled in the nine selected schools (IM). To match this, 10 schools were selected for the VM, given their lower enrolment. Schools in both models were rural and had similar student attendance and distance to the nearest eye centres (within a service radius of 5 km). At the end of the intervention period, there were 11 978 children enrolled in the schools, with 6257 children in the IM and 5721 children in the VM (Characteristics of schools, children and teachers in the integrated and vertical models