Abstract:AIM: To investigate the changes of nearwork induced transient myopia(NITM)in different refractive status after continuous near tasking.
METHODS: Prospective study. Thirty subjects(aged 18-24, average 20.9±2.1, 12 males and 18 females)were recruited in this study. They were divided into 3 groups according to the subjective refraction: 10 with hyperopia(H), 10 with emmetrope(E)and 10 with myopia(M). All the subjects with soft contact lens watched videos on a panel computer at near distance(33cm～40cm). Five measurements of distance refraction in the right eye were performed by using an infrared optometer before, after 30min and 60min sustained viewing task, and the mean of 5 refractive values was recorded as spherical equivalent. Then distance refraction of right eyes was done every 5s followed by stopping near tasking until NITM was disappeared completely and the decay time of NITM was recorded for each subject. The value of NITM was the difference of refractive values between before and after near tasking. Paired-t test was used to compare the changes of refractive values in the same group. ANOVA was used to determine the differences of NITM and its decaying time among three groups.
RESULTS: Compared with pre-task, no significant refractive changes were found in hyperopic group(t=1.627,P=0.138); While subjects with emmetropia and myopia showed more myopic shifts at the two time points(tE=2.699,PE=0.024; tM=4.930,PM=0.001). With continuous viewing until the 30th min and 60th min, significant differences of averaged NITM were found between myopic group and other 2 groups(P<0.05), but no difference was found between hyperopic group and emmetropic group(P>0.05). Significant differences of the decay time of NITM can be seen among the three groups after near tasking(F=787.983,P<0.001).
CONCLUSION: Subjects with myopia are more susceptible to produce NITM than other 2 groups during sustained nearwork for the same time and the decaying time of NITM is longer in myopia group after near tasking, thus it is suggesting that NITM might be attributed to the development and progression of myopia.
