Using Light Meters to Investigate the Light-Myopia Association – A Literature Review of Devices and Research Methods

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TL;DR

This review identifies ten wearable light meters used in human studies on light exposure and myopia, highlighting wide between-device variability in specifications and measurement. It analyzes 20 publications and finds high methodological variability, with no clear pattern linking device type or study design to the presence of a light-myopia association. The findings underscore the need for standardized reporting and device-specific validation, particularly regarding the common 1000 lux indoor-outdoor cut-off.

Full summary

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**Background:** The increasing prevalence of myopia worldwide has prompted research into adjustable environmental factors, with light exposure emerging as a potential protective factor. While time outdoors and bright light have been associated with reduced myopia in both animal and human studies, the evidence is not unambiguous, and many methodological aspects vary across investigations. This review aims to provide an overview of wearable light meters used in human myopia research and to analyze the research methods of publications investigating the light-myopia association (LMA).

**Methods:** A comprehensive literature search was conducted in PubMed and Web of Science, supplemented by reference list searches and other sources, up to January 2023. Inclusion criteria for the device analysis required human participants wearing light meters, myopia as a topic, and lux data collection. For the research methods analysis, publications had to analyze lux data as a main outcome in direct relation to refractive error/myopia or be a methodological investigation within this framework. Ten wearable light meters were identified from 40 publications, and 20 publications (18 journal articles, one dissertation, one conference poster) were included in the research methods analysis.

**Key Results:** The ten devices identified were: Actiwatch 2, Actiwatch Spectrum, Actiwatch Spectrum Plus, Actiwatch Spectrum PRO, Clouclip, FitSight, HOBO Pendant Temp/Light data logger, Mumu, MyLyt, and Vivior Monitor. These devices vary widely in lux measurement range (e.g., 1–65,528 lux for Clouclip to 0–320,000 lux for HOBO), spectral sensitivity (e.g., 400–900 nm for Actiwatch 2 vs. 150–1200 nm for HOBO), wearing position (wrist, spectacles, clothing), and sampling intervals (from 1 second to 5 minutes). Among the 20 publications, 14 studied children and 4 studied adults; 10 were cross-sectional and 8 longitudinal. The 1000 lux indoor-outdoor cut-off was used in 14 of 15 publications that employed such a cut-off, but only 3 reported own pre-measurements to validate it. Overall, 10 publications reported support for LMA (more bright light associated with less myopia), while 10 showed little or no support. Publications with larger sample sizes (e.g., >80 participants) more often supported LMA (7 of 9) compared to smaller studies (3 of 9). All three publications using Clouclip (eye-level measurement) supported LMA, while only 2 of 6 using HOBO did. The four oldest publications (2011–2013) all reported no LMA.

**Clinical Implications:** The high between-study variability in devices, methods, and results complicates the synthesis of evidence on the light-myopia association. Researchers should carefully select light meters based on study circumstances, report geographic location and season of data acquisition, thoroughly describe participant characteristics and refractive status assessment, and validate the indoor-outdoor cut-off for their specific device and setting. Standardized reporting of light exposure metrics (e.g., mean lux during waking hours) would facilitate cross-study comparisons. The finding that eye-level light measurement (Clouclip) consistently supported LMA suggests that device positioning may be critical. Future research should include more diverse geographic regions and systematically investigate the role of season, age, and sample homogeneity.