Study On The Changes In Optical Quality After Small Incision Lenticule Extraction Surgery

PurposeTo evaluate the changes in optical quality after small incision by comparing the characteristic of straylight between SMILE and femtosecond laser-assisted excimer laser in situ keratomileusis(FS-LAISK) after surgery, and evaluating the change of corneal optical quality under 3mm and 6mm pupil size after SMILE procedure using modulation transfer function and Strehl ratio. Methods1. A retrospective case study. Straylight measurement was performed on 67 myopic and myopic astigmatism patients(67 eyes) who underwent SMILE in Tianjin Eye Hospital before SMILE surgery and 1 week, 1 month, 3 month and 6 month after surgery using Oculus C-Quant straylight meter. The correlations among the straylight values with factors such as age, spherical equivalent, equivalent sphere, centeral corneal thickness(CCT), mean keratometric value,corneal curvature radius as well as with postoperative factors, such as cap diameter, hinge width, ablation depth, ablation ratio, residual bed thickness, RBT/CCT and energy were analyzed statistically.2. A retrospective study was designed. Written informed consent was obtained from each patient prior to accepting the surgery. One hundred and twenty-seven eyes of 68 patients with myopia and myopic astigmatism were included in Tianjin Eye Hospital from January 2011 to July 2013. SMILE was performed on 64 eyes of 35 patients and FS-LASIK was carried out in 63 eyes of 33 patients at the same period. Stray light was detected with C-Quant stray light meter before and 1 week, 1 month and 6 months after surgery. The changes of stray light values following the surgery were compared between the two groups, and the correlations between postoperative stray light values with operative parameters were analyzed.3. A retrospective case study. 32 myopia or myopic astigmatism patients who underwent SMILE surgery were involved in this study. Corneal optical quality was measured using Sirius ocular analysis system preoperatively and 1 week, 1 month, 3months postoperatively. Modulation transfer function and Strehl ratio values were recorded and used to analysis. Repeat-measure ANOVA was used to analysis the changes of MTF and SR pre and postoperatively. Results1. The forward straylight values were 0.93±0.16, 0.97±0.14, 0.94±0.17,0.94±0.17,0.90±0.17 pre-operation, and 1 week, 1 month, 3month and 6 month after SMILE surgery. The mean stray light value was little higher than preoperative values in 1 week after surgery while no significant differences were found. There was no significant differences in the forward light scatter among the various time points(F=2.253,P=0.076).While the change in straylight values after surgery were no correlated with the parameters in surgery while slight positively correlated with hinge width in 3 week after surgery(r=0.356 P=0.003).2. The mean stray light values were(1.03±0.19) and(0.95±0.16) at 1 week and 1 month after surgery, which were higher than(0.88±0.18) at preoperation in the FS-LAISK group(P=0.000, 0.012). The stray light values were(0.98±0.16),(0.95±0.14) and(0.94±0.16) at 1 week, 1 month or 6 months after surgery, respectively, and no statistically significant differences were found in comparison with(0.91±0.15) in preoperation in the SMILE group(all at P>0.05). No significant difference in the straylight values was found between the two groups(Fgroup=0.077, P=0.781). The postoperative and preoperative straylight values were significant differences in the FS-LASIK group compared with SMILE group during the follow-up time(Fgroup=14.798, P<0.001), with the significant difference in postoperative 1 week between the two groups(P<0.01). The weak negative correlations were found between the straylight change values⊿log(s) and the lenticule thickness/central corneal thickness(CCT) at 1 week, 1 month and 6 months after SMILE(R2=0.123, 0.145, 0.098, all at P<0.05).3. Compared to preoperative, the MTF curve of anterior corneal surface increased significantly from low to high frequency at 3mm optical zones of cornea(P<0.05) 1 week, 1 month and 3 month after SMILE procedure. And it was also found that the MTF curve of anterior corneal surface at vertical meridian increase slightly from low to high frequency under 6mm optical zones of cornea(P<0.05) during the follow-up time, especially in low to intermediate frequency(10cpd、20cpd、30cpd、40cpd). However, there was little increase of various frequency under 3 mm pupil diameter at horizontal meridian(P>0.05). The Strehl ratio showed significant increase under 3mm pupil size and 6mm pupil size, and it showed more increase at 3mm pupil size than 6mm pupil size. Conclusion1. Forward light scatter appears less change in operative eyes after SMILE. And less change would happen on the optical quality in terms of the effect of forward light scatter after SMILE surgery.2. However, it shows more increases in forward light scatter of the eyes undergoing FS-LASIK surgery compare to SMILE surgery, especially at early stage postoperatively. And the straylight returned to normal over time.3. It showed that less change would happen on the optical quality in terms of the effect of forward light scatter after SMILE surgery than that after FS-LASIK surgery.4. SMILE showed a great improvement in corneal optical quality for myopia or myopic astigmatism patients. And it was found that it will be better in photopic condition than scotopic condition.