Higher-order aberrations in eyes with visual symptoms after LASIK

Abstract

Objective To investigate the distribution of the eye's higher order aberrations in post-laser in situ keratomileusis (LASIK) patients with visual complaints,excluding patients whose complaints were due to overcorrection,undercorrection and eye disease.Methods Refractive surgery was performed on 17 625 eyes of 8848 patients from January 1,2006 to March 31,2010 in Beijing Military General Hospital.In this retrospective case-control study,a total of 48 eyes of 40 cases with double vision,glare and other visual symptoms after LASIK (including the traditional group and wavefront-guided group),excluding cases of overcorrection,undercorrection and eye disease were reviewed.As a result,there were 23 eyes of 18 cases in the traditional LASIK group and 25 eyes of 22 cases in the wavefront-guided LASIK group.Patients were observed for more than 3 months and refractive power stability was within the ±1.00 D range in both groups.The observation period for the wavefront-guided group was 10 months (4-26 months) and was 23 months for the traditional group (5-72 months). All patients were measured using a Hartmann-Shack wavefront sensor. The results for higher-order aberrations with 4-mm pupils were analyzed. The preoperative and postoperative results of the wavefront-guided LASIK group were compared (using a paired samples t test and Wilcoxon signed ranks test).The results between the wavefront-guided LASIK and traditional LASIK groups were also compared (using independent samples t tests and the Mann-Whitney test) to test for higher-order aberration root mean square (RMS) values,the distribution ratio of different aberration types in total higher-order aberrations and the dominant aberration changes (chi-square test).Results There were significant differences in higher-order aberrations in the wavefront-gnided LASIK group when aberrations were compared before and after surgery:there was an 118％ increase in total higher order aberrations (t=-11.485,P＜0.01);there was a 125％ increase in third order aberration RMS values (Z=-6.125,P＜0.01);there was a 93％ increase in fourth order aberration RMS values (Z=-6.154,P＜0.01);there was a 135％ increase in fifth order aberrations (Z=-6.154,P＜0.01);there was a 114％ increase in sixth order aberrations (t=-21.080,P＜0.01).Vertical coma increased by 143％ (Z=-6.154,P＜0.01),horizontal coma increased by 93％ (Z=-6.154,P＜0.01),and spherical aberrations increased by 89％ (t=-19.659,P＜0.01).Trefoil varied less than the other types.30° trefoil increased by 5％ (Z=-6.154,P＜0.01) and 0° trefoil increased by 35％ (Z=-6.154,P＜0.01).The results for the wavefront-guided LASIK group and the traditional LASIK group were also compared.Differences in total higer-order aberrations,third order aberrations,fourth order aberrations,vertical coma,horizontal coma,spherical aberration,30° trefoil and 0° trefoilwere not statistically significant.But the postoperative fifth order aberrations (Z=-2.033,P=0.042) and sixth order aberrations (Z=-2.631,P=0.009) showed statistically significant differences when the two groups were compared.In addition,the proportion of third order aberrations was the highest among total higher-order aberrations and fourth order aberrations were second after LASIK.The differences between the two groups were not significant.But the differences in the proportion of fifth order aberrations (Z=-2.053,P=0.040) and sixth order aberrations (Z=-2.012,P=0.044) were statistically significant between the two groups.Coma aberrations accounted for 56％ of the third order aberrations and spherical aberration accounted for 78％ of the fourth order aberrations before and after wavefront-guided LASIK.But trefoil decreased significantly from 43％ to 36％ of the third order aberrations after wavefront-guided LASIK (t=2.285,P=0.027).The proportion of vertical coma was 44％,horizontal coma was 12％ and spherical aberration was 40％ among the dominant aberrations after wavefront-gnided LASIK and the differences between preoperative and postoperative levels were statistically significant (x2=7.891,P=0.048).The proportion of vertical coma was 30％,horizontal coma was 34％ and spherical aberration was 21％ among the dominant aberrations after traditional LASIK. There were no statistically significant differences between the two groups.Conclusion Visual complaints after LASIK are closely related to the increase in higher-order aberrations.The RMS values of higher-order aberrations are generally higher than preoperative levels except for trefoil aberrations.The third order aberrations and the fourth order aberrations account for a large proportion of the higher-order aberrations.Coma and spherical aberration are especially important.Trefoil varis less than other types.Traditional LASIK is superior to wavefront-guided LASIK on the ablation of fifth order and sixth order aberrations.Coma and spherical aberration are the dominant aberrations in patients with visual symptoms after LASIK. Key words: Keratomileusis,laser in situ; Higher-order aberrations; Vision disorders; Case-control studies