Nearwork-Induced Transient Myopia in Emmetropes and Myopes

Abstract

Abstract: : Purpose: Literature shows that there is a putative link between nearwork and the onset, as well as growth, of myopia. A transient effect, nearwork-induced transient myopia (NITM) usually happens after a period of near fixation. Our group has worked on Chinese myopic and emmetropic children on this NITM before. This study determines and compares the magnitude and time course of the accommodative and pupil size response in myopic and emmetropic non-Chinese adults. Methods: Thirty subjects (19F) with mean age of 20.90 (± 3.18) years joined the study. Emmetropes (n = 13) with mean spherical equivalent (MSE) of –0.13 (± 0.27) D and myopes with MSE of –3.52 (± 2.72) D were recruited. A Badal lens system was used and the subjects were required to fixate a 5.00 D accommodative demand (they were 0.00 LogMAR letters) monocularly for 5 minutes, and then an equivalent target at optical infinity for 3 minutes. Dynamic accommodation of the right eye was measured by a modified Shin-Nippon open-field autorefractor, SRW5000, while the pupil size of the other eye was monitored by a video capturing system. Myopic subjects were required to wear disposable contact lenses throughout the experiment. Results: The mean accommodative responses of myopic subjects (near: 3.81 ± 0.46 D; optical infinity: 0.04 ± 0.36 D) were statistically similar with the emmetropic subjects (near: 3.98 ± 0.38 D; optical infinity: 0.07 ± 0.29 D) (p > 0.05). The mean difference between the accommodative response and demand at near was similar between the two groups (emmetropes: 1.02 ± 0.38D; myopes: 1.19 ± 0.46D) (p > 0.05). The mean difference between accommodative response and demand after the near fixation, i.e. NITM, was also similar between the two groups (emmetropes: 0.07 ± 0.30 D; myopes: 0.03 ± 0.37 D) (p > 0.05). Both groups demonstrated a significantly bigger pupil size during fixation at optical infinity than that at near (p 0.05). The association between change in accommodative response and change in pupil size was very weak in both groups (myopes: p > 0.05, r = 0.20; emmetropes: p > 0.05, r = 0.09). Conclusions: There is no significant post-task NITM in both emmetropic and myopic non-Chinese adults. This non-parallel result to our previous experiment done with the same protocol for HK children may suggest a different accommodative response in different ethnical and age groups.

Keywords: accommodation • myopia • pupil