A novel instrument for logging nearwork distance

Purpose: To validate a novel ultrasonic sensor for logging reading distances. In addition, this device was used to compare the habitual reading distances between low and high myopes. 

Methods: First, the stability and sensitivity of the ultrasonic device were determined by repeated measures using artificial targets. Then, thirty Hong Kong Chinese (20-30years) were recruited, of whom fifteen were considered to be high myopes (mean±S.D.=-8.7±0.5D) and 15 to be low to non-myopes (mean±S.D.=-2.0±0.2D). Each subject read a newspaper with their habitual visual aid continuously for 10min in two sessions at their preferred working distance(s). The reading distances were recorded continuously using a novel nearwork analyzer. The modal working distance was considered as the 'habitual' reading distance. In addition, habitual reading distance was reported orally by each subject. 

Results: The nearwork analyzer gave accurate and repeatable measurements over a range of distances and angles. Using this instrument, high myopes were found to have a significantly shorter reading distance than low myopes or non-myopes (mean±S.D.=35.9±9.8cm vs 50.9±24.8cm; two-sample t-test, p=0.04, df=18). The reading distances reported orally by the subjects were not correlated with those recorded by the nearwork analyzer. 

Conclusions: The nearwork analyzer was found to be an effective tool for measuring nearwork reading distance in a small group of emmetropic and myopic adults over a 10min interval. Differences between the reading distance between high myopes and low/non-myopes was detected by the device. Further study is needed to determine if a closer working distance is a cause or effect of myopia development.