Beyond Screen Time: A Measurement Framework for Behavioral Exposures in Childhood Myopia

Childhood myopia is increasingly discussed in relation to digital device use, yet total screen duration is biologically nonspecific (not tied to a single biological cause) and may combine outdoor-light deficit, near work intensity, educational routines, and sleep/circadian timing. This critical narrative review used structured database searches to support transparent source identification, not systematic completeness, quantitative pooling, or formal risk-of-bias grading. We narratively appraised evidence by design, exposure specificity, outcome specificity, temporality, and clinical directness, then derived a measurement framework. Outdoor light exposure has the strongest support for preventing incident myopia. Near work and the visual demands of schooling are important, but they are measured in inconsistent ways. Sleep and circadian timing remain biologically plausible, albeit lower-certainty modifiers. Digital device metrics are best interpreted as contextual measurement markers that can recover timing, bout structure, task context, substitution, and adherence, rather than as standalone causal surrogates (stand-ins for a true cause). The proposed framework prioritizes direct measurement of outdoor light, near work intensity, sleep/circadian timing, and axial-growth outcomes, using device-related behavior only when it clarifies daily exposure patterns. This is a narrative review of previously described behavioral factors; it does not identify new risk factors or propose a novel causal model. For measurement, it groups these behaviors by how they occur together across a single day and separates substitution, mediation, interaction, and temporal clustering as distinct estimands (the specific quantities to be estimated). Its purpose is to improve exposure measurement and hypothesis testing, not to establish digital device use, sleep timing, or clustered routines as independent causal risk factors.