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Using The Smartphone to Measure Near Work Distance


Purpose: Part of the large increase of myopia prevalence in children is due to prolonged use of electronic screens (smartphones and tablets) at near-work distances. Myopia progression is correlated with near vision. However, there are no commercially available solutions to measure work distance in natural conditions at high acquisition rates. We developed an application (VisionApp, for the Android OS, capable of measuring the distance between the user and the device in real time. We test its accuracy and precision. Methods: We used the front camera of two smartphones of different brands: Xiaomi Mi5s, and Samsung Galaxy S6+ to acquire images of two subjects at varying distances, at a rate of 30 FPS. The head was fixed using a chin rest. The device was mounted in a holder affixed to a stepper motor, which allowed the distance to the subject to be precisely controlled. The distance between the subject and the device was measured within the range from 190 to 420mm in 10mm steps. Three consecutive measurements were obtained at each distance in each case. Both devices were calibrated by means of applying a calibration factor CF, which accounted for differences in proprietary device parameters, such as the ratio between total and active camera sensor area. The CF was measured at 5 distances from the subject (200, 250, 300, 350 and 400mm), and found to be the same for the same device. Results: Linear fit to the smartphone-measured distance in function of real, stepper motor-controlled distance showed a slope of 1.110 (R2=0.99) and 0.978 (R2=0.99) for Xiaomi and Samsung, respectively. The mean and SD was 11±10 mm and 5±10 mm for Xiaomi and Samsung, respectively. The calibration factor CF obtained for Xiaomi was 0.87±0.03, and 1.15±0.03 for Samsung. The mean maximum CF variation for different distances was 6.5%. Conclusions: We have developed and evaluated a new app that can be used to measure the work distance between the user and the device. The main benefit is that the app runs on the very device, eliminating the need for any extra equipment. The accuracy of the distance measurement was ~1 cm. The accuracy did not depend on the model of smartphone used, nor the calibration distance (calibration can be performed at any distance and assure the same, high accuracy). The app was designed to store the measurement data in the device and can be used in parallel with other running applications. It can be a suitable tool for research or clinical studies that aim to evaluate the distance between a user and an electronic device under natural conditions.
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... A very simple method of distance measurement was employed. In recent years, wearable devices 20,21 and apps 22 were developed for real-time monitoring of near-work distance. This methods may results in a more accurate analysis of subjects' behavior, but need to be installed on the device or to be worn by the subject, being more invasive, time-consuming, and expensive. ...
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Purpose: The aim of this cross-sectional observational study was to measure habitual viewing distance with smartphones in individuals of different ages, and to identify factors influencing viewing distance. Material: Gender, reading position, forearm length, ametropia, correction modality, and near vision quality were investigated as factors affecting viewing distance. Participants were asked to read a typical text message on their own smartphone, while sitting and standing. A total of 233 subjects (129 females and 104 males), aged from 16 to 90 years old, were included and divided in two groups: 131 non-presbyopes (median 21.1, range 16 - 39), and 102 presbyopes (median 54.5, range 42 - 90). Results: Mean viewing distance was 36.1 ± 7.2 cm while sitting, and 37.4 ± 6.8 cm while standing (P < 0.05), and 36.8 +/- 6.6 cm overall. The average viewing distance was 35.0 ± 6.4 cm in non-presbyopes, and 39.0 ± 6.1 cm in presbyopes (P < 0.05). The average viewing distance was 34.7 ± 6.2 cm in females, and 38.2 ± 6.3 cm in males (P < 0.001). Conclusions: Significant differences between males and females were observed, due to the different average body size between the two gender groups. Average viewing distance with smartphones in presbyopes matched approximately to the typical near reading distance of 40 cm. In the non-presbyopic group, the accommodative demand when reading a smartphone was slightly higher than in the presbyopic group. High variability was observed in both age groups, without a statistically significant correlation with other assessed factors as reading position, ametropia, correction modality, and near vision quality.
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