Research on the simulation method of experiencing night myopia on the ground

Objective To establish a simulation method that enables pilots to experience night myopia and help them to improve the understanding of it and its hazards to flight safety. Methods The self-made visual object was a 2 mm-diameter light emitting diode (LED) lamp with controllable luminous intensity. Twenty volunteers with normal vision (≥1.0) were asked to search the target light 6 m away as they adapted the environment in a standard dark room for 20 min. The subjects were guided to slowly move (10-20 cm/s) toward the target light until they saw it. The moment of seeing the object target light was marked as time A and the distance between visual object and subject was marked as LA. Then the subject was asked to stare at the target light and slowly moved apart from the target light until he/she couldn't see it. The target losing moment was marked as time B and the distance between target light and subject was marked as LB. Tobiipro Glass Ⅱ was used to record eye movements and pupil changes in real time. A manual optometry screening instrument (SW-800) was used to detect the refractive diopter under normal indoor lighting condition and the refractive diopters at time A and time B. The degree of night myopia was calculated according to the refractive diopter change and the displacement between LA and LB (LAB). The effects of the luminance of the target light (low: 1×10-3 cd/m2, medium: 2×10-3 cd/m2, high: 3×10-3 cd/m2) and the correction of negative spherical lens (+ 0.5 D and + 1 D) on the experimental results were analyzed. One-way analysis of variance was used for statistical analysis. Results The subjects, diopter was respectively (-0.194±0.390)D, (-0.509±0.532)D and (-0.836±0.700)D corresponding to under normal luminance, at time A and at time B. The significance was observed among these 3 conditions (F=6.679, P<0.01). The record of eye movement was consistent with the subject's report. Subject's pupil tended to dilate as soon as the target light was seen. When subjects wore + 1 D spherical correction lens, the results indicated longer LA and shorter LAB comparing to the unaided observation (P<0.05). The LAB under medium and high luminance target light was significantly shorter than that under low luminance (P<0.05). Conclusions This method can effectively simulate night myopia effect and assess the myopia, improve the understanding of night myopia, and is suggested to apply to pilot's experience in ground training. Key words: Myopia; Refraction, ocular; Dark focus; Ambient luminance; Night; Simulation