Reap more than sow: Experimental evidence of spillover effects from free eyeglass distribution among rural students in China

Using a randomized controlled trial across 31 rural junior high schools in China, this study examines the spillover effects of providing free eyeglasses to myopic students on the visual health of their non-myopic peers. Within one school year, the intervention significantly reduced visual deterioration among non-myopic students by 0.48 lines and lowered new myopia incidence by 10 percentage points (a 24.3% decline), while also improving eye-use behaviors. These spillovers cannot be explained by conventional interaction-based or shared environmental mechanisms typically emphasized in non-infectious health interventions. Instead, they are more consistent with observational social learning: non-myopic students observe peers being diagnosed with myopia and required to wear eyeglasses, which increases their awareness of vision risks, updates their risk perceptions, and shapes their attitudes toward eyeglasses, thereby prompting protective behavioral changes. This mechanism extends positive spillover effects beyond context-specific interventions (e.g., infectious diseases) to a broader range of health interventions, and offers new insights into the prevention of non-infectious conditions such as myopia.