Validation of real-time viewing distance and ambient illumination measurement with two wearable sensors.

Purpose: To report the repeatability and accuracy of viewing distance and ambient illumination measured with the Vivior and Clouclip wearable sensors in a controlled laboratory setting and while young adults performed different near visual tasks.

Methods: For Study 1, viewing distance and ambient illumination were measured repeatedly for 2 days with two sensors mounted on a mannequin. Results were compared with standard measures (ruler, lux meter) using linear regression and Bland-Altman analysis. In Study 2, viewing distances were captured in 13 young adults while they performed four near tasks for 20 min each (reading a printed article, reading an article on an iPad, typing on a laptop or watching videos on an iPad) under three illuminations (500, 250 and 25 lux). Results were compared between the devices and with a standard ruler and differences tested statistically using ANOVA and Tukey's multiple comparison tests.

Results: In Study 1, a positive linear relationship was observed between viewing distances measured by each sensor and the standard ruler (mean [SD] difference of -0.12 cm [0.23] for Vivior, -0.18 cm [0.51] for Clouclip), with good repeatability (mean [SD] difference between 2 days was 0.02 cm [0.24] for Vivior, -0.14 cm [0.35] for Clouclip). A positive linear relationship was also observed between illumination measured by each sensor and the luxmeter (mean [SD] difference of -16.85 lux [325.5] for Vivior, 39.12 lux [335.6] for Clouclip). In Study 2, the viewing distances during the four near tasks were not significantly different between the three methods used. Shorter working distances were measured with all methods when reading a printed article compared to typing on a laptop and watching a video on the iPad (all p < 0.05).

Conclusion: Vivior and Clouclip are recommended for real-time capture of near vision duration, distance and light exposure in future studies aiming to understand the effect of habitual visual environment.