Myopia is on the rise—due in part to our screen-reliant culture—and a recent study supports what we’ve suspected but haven’t yet implemented: limiting smart device usage to under two hours a day. In our current pandemic-induced reliance on virtual classrooms and remote workplaces, this data-backed suggestion seems like an even steeper hill to climb.

Smart devices in particular were the focus of this recent study, as reading distance tends to be much closer with these smaller screens compared with computer desk work. Additionally, while flicker rates are a thing of the past, eye-straining brightness and rapid scrolling through social media further separates these devices from computers.

The Hong Kong public health study encompassed a representative sample of 1,597 children and adolescents and measured their one-year change in refractive error. Participants self-reported smart device usage, and the researchers took into account factors such as age, sex, baseline spherical equivalent refraction, parental myopia, body mass index, socioeconomic status and exercise.

The researchers reported that those who spent more than two hours per day using a smart device experienced a significant negative shift in refractive error (-0.25D vs. -0.09D) of the right eye and a marginally significant negative shift (-0.28D vs. -0.15D) in the left eye.

Interestingly, the researchers noted that children who spent more time on smartphones but limited their tablet usage demonstrated greater negative shifts in refractive error than those who spent more time on both devices. “These results suggest that prolonged smartphone usage may present a higher risk of myopia progression than tablet usage,” they wrote in their paper.