*2.2. Construct Measures*

In order to facilitate the investigation, items on the questionnaire prompted respondents to self-evaluate symptomatic changes in their vision condition using the Lay Terms Approach, which advised using terminology that subjects are familiar with [22], such as "blurry vision when looking at distant objects" or "the need to squint." The standardized questionnaire also collected information on time (hours) spent using e-learning devices such as TVs, computers, or smartphones, and how frequent subjects engaged in outdoor exercise, as well as their subjective ratings of indoor lighting condition (too dim, too bright, or feels okay) while using e-learning devices. Following previous studies, we classified e-learning device use into three categories by device type—near (0.1 m for smartphones), intermediate (0.5 m for computers), and far (0.8 m for TVs)—and calculated daily digital screen use in diopter hours (dh), which is a viewing-distance weighted measure of near-vision exposure to digital devices [23].

dh = (3 × hours viewing at 0.1 m) + (2 × hours viewing at 0.5 m) + (1 × hours viewing at 0.8 m)
