The Accommodative Changes After LASIK And The Difference Of Anterior Segment Changes During Accommodation Before And After LASIK In Myopia

BackgroundLaser in situ keratomileusis(LASIK) has quickly become one of the most popular procedures to reduce or eliminate myopic refractive error for its rapid recover of vision and little pain. Nowdays, more than a million procedures performed each year all around the world. Although the overall satisfaction was high and most patients were satisfied with their uncorrected visual acuity and visual recovery, quite a few patients whose visual acuity was20/20maybe complain of compromises in visual quality and comfort. Visual discomfort and difficulty in reading have been one of the most frequent symptoms after LASIK. Although there are many potential sources associated with asthenopia after surgery, accommodation disturbances may be the main cause for near-vision complaints.Some researchers found the amplidtude of accommodation is reduced in early days after LASIK, however, the other factors related to accommodation were still not known and the mechanism of accommodation disturbance was not full understood as yet. The purposes of these studies are to evaluate the all changes of accommodative functions and asthenopia after LASIK in myopes and to compare the changes of anterior segment resulted from accommodation before and after surgery.Part1. Influence of LASIK on accommodation and asthenopia in myopiaObjective:To evaluate the changes of accommodation and asthenopia after LASIK in myopia.Methods and materials:Sixty-four myopic patients (128eyes) who were going to receive standard LASIK were enrolled in this study with the age from18to40years and were divided into two groups:low to moderate myopic group(>-6.0D),and high myopic group(≤-6.0D).According to the age, the patients also were categorized into two groups:<30years and≥30years. Amplitude of accommodation,negative and positive relative accommodation,monocular accommodative facility and lag of accommodation were measured before and lweek,1month and3months after surgery. At the same time, asthenopia were scored by questionair.Results:1.Amplitude of accommodation(AMP):The mean AMP was decreased significantly in all groups at1week after LASIK(all p<0.05),and rehabilitate to preoperative level except the elder group at1month postoperatively. There was no significant difference between before and3months after LASIK in AMP in low to moderate myopic group and younger group(all p>0.05). The AMP was significantly increased in high myopic group and elder group3months after LASIK compared with preoperation(LSD, all p<0.05).2. Negative relative accommodative (NRA): There was no significant difference in NRA in all groups between before and after surgery(all p>0.05).3.Postive relative accommodation (PRA):The mean PRA was decreased significantly in all groups at1week after LASIK (all p<0.05), and recovered to preoperative level at one month after LASIK(LSD, all p>0.05). The PRA was significantly increased in high myopic group at3months after surgery compared with preoperation (LSD, all p<0.05).4.Monocular accommodative facility (AF):The mean AF was9.80±2.39CPM、8.16±1.77CPM、9.96±2.09CPM and11.70±2.39CPM before LASIK and one week, one month,and three months after LASIK in low to moderate myopic group, respectively (F=183.151, P=0.000) The mean AF was8.42±1.48CPM.6.55±1.15CPM、8.52±1.68CPM and10.07±1.79CPM in high myopic group before LASIK and one week, one month,and three months after LASIK (F=181.595, P=0.000). The AF was decreased significantly at one week after LASIK in all groups compared with preoperation (LSD, all p<0.05).One month after surgery, there was no significant difference between preoperative AF and postoperative AF in all groups(LSD, all p>0.05).The mean AF was significantly increased at3months after surgery compared with preoperation(LSD, all p<0.05).5.Accommodation response:Both at3.0D and5.0D accommodative stimulus, the lag of accommodation (LOA) was significantly increased in all groups at one week after LASIK(all p<0.05), and recovered to preoperative level at one month after LASIK(LSD, all p>0.05).3months after surgery, the LOA was significantly decreased in high myopic group and elder group compared with preoperation (LSD, all p<0.05).6.Asthenopia score:The mean asthenopia score was increased significantly at one week after LASIK in all groups compared with preoperation (LSD, all p<0.05).One month after surgery, there was no significant difference between preoperative mean asthenopia score and postoperative mean asthenopia score in all groups(all p>0.05).The mean asthenopia score was significantly decreased in high myopia group and two age groups at3months after surgery compared with preoperation(p<0.05). The preoperative asthenopia score had significant effect on1week-postoperative asthenopia score by multiple linear regression analysis (T=7.458, P=0.000). The preoperative asthenopia score, spherical equivalent, PRA, amplitude of accommodation(minus lens) and lag of accommodation had significant effect on3month-postoperative asthenopia score (P=0.000,0.000,0.005,0.015,0.035)Conclusion:Most of the parameters of accommodation show decreased in early days after LASIK,and almost all can guadually recovered in one to three months. Some of them may become better than before surgery3months after LASIK. So LASIK may be good for the accommodative function in myopes in the long run. Part2. Anterior segment changes during accommodation in myopiaPurpose:To evaluate anterior segment changes during accommodation in different degree myopia.Methods:Sixty myopes with the age from18to39years were enrolled in this study and were divided into two groups:low to moderate myopia group(>-6.0D),and high myopia group(≤-6.0D).Anterior segment measurements were performed by anterior segment optic coherence tomography (OCT) under three different accommodative state of relax (0.0D),3.0D and5.0D. The posterior corneal curvature(PCC), anterior chamber depth (ACD), lens thickness (LT), pupil diameter(PD) were compared at different different accommodative state using repeated measures ANOVA.Results:Low to moderate myopia group comprised32myopes with the mean age29.34±4.65years, mean spherical equivalent-3.72±1.05D; High myopia group comprised28myopes with the mean age29.57±5.89years, mean spherical equivalent-7.05±0.85D; With the accommodation relaxed(OD), there was no difference between the low to moderate myopia group and high myopia group both in PCC and LT, ACD was2.92±0.23mm in high myoia and2.67±0.19mm in low to moderate myopia (T=-4.637, P=0.000). pupil diameter was6.21±0.56mm in low to moderate myopia and5.95±0.42mm in high myopia (T=2.011, P=0.049).With the accommodation increased, ACD decreased significantly, LT increased significantly, and PD decreased significantly in both groups (all P<0.05). The PCC has no significant change during accommodation in both groups(all p>0.05).Conclusions:Anterior segment OCT can find the alteration of ACD,LT and PD with accommodation. During accommodation,the cornea is stable with anterior segment OCT. Part3. comparison of the changes of anterior segment resulted from accommodation before and after LASIK in myopiaObjective:To evaluate the difference in changes of anterior segment resulted from accommodation between before and after LASIK in myopia.Methods:Sixty myopic patients with the age from18to39years who were going to undergo standard LASIK were enrolled in this study and were divided into two groups:low to moderate myopic group(>-6.0D),and high myopic group(≤-6.0D). Anterior segment measurements were performed by anterior segment optic coherence tomography (OCT) in undominant eye under three different accommodative state of relax (0D),3.0D and5.0D before LASIK and one week one month,and3months after LASIK. The changes in posterior corneal curvature(PCC), anterior chamber depth (ACD), lens thickness (LT), pupil diameter(PD) with accommodation at different time after LASIK were compared with those measured before LASIK.Results:There were no significant difference between preoperative PCC, ACD, LT, PD and those of postoperation at the state of non-accommodated in both groups(all p>0.05). Compared with preoperation, the mean changes of LT induced by3.0D and5.0D accommodation and the mean changes of ACD induced by5D were significantly decreased in both groups at1week postoperatively (LSD, all p<0.05). There were no significant difference between preoperative alteration in anterior segment induced by2level’s accommodation and1-month postoperative alteration in both groups(all p>0.05). The mean changes of LT induced by5.0D accommodation were significantly increased at3months after surgery compared with preoperation in high myopia group(LSD, p<0.05).Conclusions:The changes of LT and ACD induced by accommodation in myopia seem to be decreased in the early days after LASIK and may recover or even increase at one to three months, which may be the mechanism that accommodative function changes after LASIK.