To explore the effects of laser irradiation parameters (irradiation frequency and single duration) on tear secretion, lens and retina.
Thirty-six healthy guinea pigs were randomly divided into 6 groups with random number table method according to different frequency and single exposure duration of laser to the eye, namely, high frequency short time (HFST) group, high frequency long time (HFLT) group, medium frequency short time (MFST) group, medium frequency long time (MFLT) group, low frequency short time (LFST) group and low frequency long time (LFLT) group, 6 for each group.The right eyes were irradiated with 500 lx laser as experimental eyes, and the left eyes of the guinea pigs served as the control eyes.The high, medium and low irradiation frequencies were defined as 15 times, 10 times and 5 times, respectively, and the short and long period was defined as 30 seconds and 60 seconds each time, respectively.The right eyes were irradiated based on the grouping at a 10-minute interval.The tear secretion was detected by SchirmerⅠtest; lens opacity was assessed under the slit-lamp microscope; fundus photography was performed to evaluate the general morphology of retina; retinal function was evaluated by electroretinogram (ERG) record and the thickness of retinal outer nuclear layer was measured by histopathology examination.This study protocol was approved by the Medical Ethics Committee of Air Force Military Medical University (No.20181203), and the use and care of the experimental animals complied with the ARVO statement.
The tear secretion was 8.00(7.37, 9.00), 8.75(8.25, 9.00), 8.50(7.75, 9.50), 9.00(8.50, 9.50), 8.00(7.37, 8.75) and 8.25(7.75, 8.75) mm/5 min in the HFST group, HFLT group, MFST group, MFLT group, LFST group and LFLT group, respectively, without significant difference among the groups(χ2=5.502, P=0.240); after laser irradiation, there were no statistically significant differences in tear secretion between the control eyes and laser-irradiated eyes in all the groups (all at P>0.05). The lenses were clear and the fundus was normal through the experimental duration in all the groups.The amplitude of ERG a-wave was significantly reduced in the HFST group in comparison with the LFST group (P<0.05), and there was no significant difference in the b-wave amplitude among the six groups (F=1.358, P=0.268). The ERG a-, b-wave amplitudes were not significantly different between the control eyes and laser-irradiated eyes in various groups (both at P>0.05). There was no significant difference in the thickness of the outer nuclear layer of retina among the HFST group, HFLT group, MFST group, MFLT group, LFST group and LFLT group (F=0.952, P=0.463).
The 500 lx laser irradiation is safe to ocular surface and lens, but there are some injuries to retinal function, and the injury degree is related to laser irradiation frequency.