Background issues

Road traffic crashes kill more people aged 5 to 29 years worldwide than any other cause and are predicted to become the 7th leading global cause of death for all ages by 2030. New research suggests that drivers with poor vision from Low and Middle-Income Countries (LMIC) are 46% more likely to involved in road traffic crashes than those without visual impairment. The prevalence of myopia, a condition that causes poor distance vision, exceeds 90% in some Asian settings and it is estimated that half the world’s population will be myopic by 2050. Uncorrected myopia among young adults in Vietnam—the age group at greatest risk for road traffic death—accounts for 93% of all vision impairment. STABLE is designed to assess the impact of vision correction on the safety of road users in a LMIC setting.

Trial design

STABLE (Slashing Two-wheeled Accidents by Leveraging Eyecare) is a stepped-wedge cluster randomised trial (SW-CRT) design involving 875 university students. It uses a SW-CRT design because, in a conventional parallel group cluster randomised trial, half the clusters would be randomly assigned to the intervention condition and half to the control condition. This approach would necessitate identifying participants with un- or under-corrected myopia and withholding glasses from them if they were randomly assigned to the control group until after the completion of the trial. The STABLE investigators maintain that it would be unethical to withhold glasses from motorcycle drivers who have been identified as needing them through the trial’s processes for this length of time. Therefore, working with local stakeholders in Vietnam they agreed on the use of the SW-CRT design, which balances the need to conduct a randomised evaluation of the intervention with the ethical demand to provide glasses to trial participants as soon as their need for vision correction is identified. All students in need of glasses will receive them.


STABLE will determine whether the provision of glasses for the correction of myopia can reduce the average number of crash-near-crash (CNC) events among motorcycle drivers in Vietnam. STABLE’s primary outcome is CNC events per 1,000 km driven as measured by GPS and a gyroscopic sensor-video data-acquisition system (DAS) mounted to the motorcycles of trial participants. CNC events will be monitored continuously over the course of the trial.

A positive trial outcome would demonstrate the safety benefits of vision correction and would create pressure for tighter regulation of drivers’ vision and the promotion of vision correction.


18 months. Identifier: NCT05466955