Changes in amplitude of accommodation in the early stages after LASIK for myopia

Objective:To investigate changes in the amplitude of accommodation in the early stages after excimer laser in situ keratomileusis(LASIK) and the relationship between postoperative accommodative amplitude and asthenopia.Methods:64 myopic patients(128 eyes) who underwent myopic LASIK were included in this study. The average age of patients was(23.80±5.08)years (18～46 years),30 patients(60 eyes) were male and 34 patients(68 eyes) were female. The pre-operative spherical equivalent(SE) was(-5.57±2.00)D,astigmatism for all myopic patients in this study was less than 2.00 D and best corrected visual acuity(BSCVA) was more than 0.8 D. The myopes were divided into 2 groups according to pre-operative refractive status:medium and low myopes with pre-operative SE ≤-6.00 D(38 cases 76 eyes) and high myopes with pre-operative SE -6.00 D(26 cases 52 eyes). 30 emmetropes[60 eyes,average age(23.64±3.65)years,SE -0.50～+0.50,BSCVA ≥0.8] were selected as controls. Accommodative amplitudes for emmetropes and myopes before surgery,1 week,2 weeks,1 month,2 months and 6 months after surgery were measured at near point and symptoms of asthenopia were assessed by questionnaire. The TOPCON 8100 autorefractor was used for refractions. The corneal flap was created using Moria 2 microkeratome followed by stromal ablation using Visx Star S 2 excimer laser. One surgeon performed all surgeries. Data was analyzed by the F test,q test,t test,H test,etc.,with SPSS statistics software.Results:Before LASIK,accommodative amplitudes for the myopes were significantly lower than for the emmetropes(P0.001). There was a sudden drop in the accommodative amplitude(P0.001) 1 week postoperatively,and the range of the decrease was positively correlated with pre-operative refractive power(r=0.52,P0.001). 1～2 months after LASIK,accommodative amplitude recovered to or surpassed the pre-operative level(P0.001),stabilized at 6 months,and there was no significant difference between the myopes and emmetropes(P0.05) after 1 month. The accommodative amplitude for high myopes was lower than that for the medium and low myopes before surgery(P0.05). There was a sudden drop in the accommodative amplitude for both groups(medium and low myopes P0.05,high myopes P0.001) 1 week postoperatively,and the range of decrease for high myopes was greater than that for medium and low myopes(P0.05). The accommodative amplitude for both groupsthen increased sharply. 2～6 months after LASIK,there was no significant difference between the two groups(P0.05). Pre-operatively,symptoms of asthenopia were more severe in the myopes compared to the emmetropes(P0.001). 1 week after LASIK,symptoms of asthenopia were severely aggravated(P0.001). 2～6 months after LASIK there was relief from the symptoms and there was significant improvement compared to pre-operative symptoms(P0.001),but they were still more severe than symptoms in the emmetropes(P0.05). Correlation analysis showed that symptoms of asthenopia appeared to have a negative correlation with accommodative amplitude(r=-0.52,P0.001). Symptoms of asthenopia were more severe in the high myopes than in the medium and low myopes before surgery(P0.05). 1 week postoperatively,symptoms in both groups were worse than pre-operative levels and the high myopes had more severe symptoms than the medium and low myopes(P0.05). Symptoms of asthenopia in both groups then eased progressively and there was no significant difference between the two groups 1 month after surgery(P0.05).Conclusion:After LASIK,the accommodative amplitude appears to decrease temporarily;the range of the decrease was correlated with pre-operative refractive power and then recovered progressively. LASIK may have no harmful effects on the postoperative amplitude of accommodation and symptoms of asthenopia. And symptoms of asthenopia are correlated with accommodative amplitude.