Continuous Objective Assessment of Near Work

Abstract

Evidence regarding the role of near work in myopia is conflicting. We developed the RangeLife, a device for continuous, objective measurement of working distance. Four devices were built, calibrated, and validated. Then, adult subjects wore the device on weekdays and weekend days, while simultaneously wearing an actigraph device for objective measurements of light exposure and activity. Subjects maintained an activity log and answered a visual activity questionnaire. RangeLife data were downloaded and binned into 0.10 m intervals. Objective diopter hours (dh), a weighted measure of near work, were calculated. Diopter hours for all subjects were significantly higher on weekdays (14.73 ± 4.67 dh) compared to weekends (11.90 ± 4.84 dh, p = 0.05). 94 ± 1.85% of near and intermediate viewing distances were recorded when the subjects were exposed to mesopic and indoor photopic light levels (<1000 lux), and 80.03 ± 2.11% during periods of sedentary physical activity (<320 counts per minute). Subjective reports of time viewing near and intermediate distances significantly overestimated objective measures (p = 0.002). The RangeLife was shown to provide reliable measures of viewing distance, and can be further utilized to understand potential influences of viewing behaviors on refractive error.

Conflict of interest statement

Dr. Edwin Ostrin and Dr. Lisa Ostrin are coinventors on a provisional patent for the RangeLife device, No. 62/608,755; managed by the University of Houston.

Figures

Figure 1

(A) Representative example of raw data from one RangeLife device as it is moved away from a wall from 0.05 to 1.0 m in 0.05 m steps approximately every 150 seconds. (B) Linear regression (solid line) showing the relationship between actual distances versus device-measured distances for each of the four devices. Dashed line represents the 1:1 line. (C) Infrared beam diameter with distance from a surface. Solid symbols are measured values and open symbols are extrapolated from the linear regression (solid line). Error bars represent standard deviation for the four devices.

Figure 2

(A) Raw distance data collected at 1 Hz from the RangeLife for one representative subject on a weekday, 9:00 am to 5:00 pm. Gaps in the data represent “out-of-range” viewing, >1200 mm. Numbers 1–9 represent activities from the subject’s activity log, and are listed in panel (B).

Figure 3

Objectively measured mean daily time (mean hours ± standard error) viewing distances from 0.1 to greater than 1.0 m for weekdays (solid bars) and weekends (open bars). Time spent viewing distances from 0.5 to

Figure 4

Objectively measured working distance (RangeLife) plotted with illuminance (lux) and activity counts per minute (cpm) as measured with the Actiwatch for a representative subject (A,B) and all subjects (C,D, mean ± standard error).

Figure 5

Objectively measured time spent viewing near to intermediate distances versus subjectively reported time for weekdays (solid symbols) and weekends (open symbols). Line represents 1:1 relationship.