To evaluate the effects of static eyeball rotation and decentration of lenticule on astigmatism correction in femtosecond small incision lenticule extraction (SMILE) by using standardized vector analysis.

A series of case observation study was performed.A total of 128 eyes from 73 myopic astigmatism patients undergoing SMILE from January to April 2019 in Henan Eye Hospital were enrolled.The preoperative spherical equivalent was -2.25 to -7.75 DS, and the astigmatism was -0.25 to -3.75 DC.The absolute value of the static rotation intraoperatively was measured by WASCA aberrometer, CRS master and MEL80 excimer laser system.The decentration of lenticule was measured and calculated according to Pentacam corneal topography and operation video.The visual acuity, refraction, corneal topography, and target induced astigmatism vector (TIA) were measured and calculated preoperatively and 1 week, 1 month and 3 months postoperatively.The results of manifest refraction were used to calculate surgically induced astigmatism vector (SIA), magnitude of error (ME), absolute value of angle of error (|AE|), absolute value of difference vector (|DV|), correction index (CI) and index of success (IS) three months postoperatively.Written informed consent was obtained from each patient before the surgery.This study protocol was approved by Ethic Committee of Henan Eye Hospital.

The absolute value of intraoperative static rotation was 2.75° (1.26°, 4.48°), decentration of lenticule was (172±87)μm and TIA was 0.69 (0.44, 1.35) preoperatively.The SIA was 0.67 (0.42, 1.10), ME was 0.10 (0.00, 0.26)DC, |AE|was 0.35° (0.00°, 9.47°), |DV|was 0.25 (0.00, 0.50), CI was 0.91 (0.72, 1.00), IS was 0.23 (0.00, 0.56) three months postoperatively.The differences of static eyeball rotation angle, ME, |DV|, CI between different astigmatism groups, the difference of decentration of lenticule between different static eyeball rotation groups, and the differences of static eyeball rotation angle, ME, |AE|, |DV|, CI and IS between different decentration groups were statistically significant (all at P<0.05). The decentration of lenticule was positively correlated with static eyeball rotation (r_s=0.39, P<0.01), and with |DV| (r_s=0.31, P<0.01).

SMILE is effective procedure in correcting astigmatism.The static eyeball rotation and the decentration of lenticule are slight.The decentration of lenticule may have a relationship with static eyeball rotation and the difference vector of astigmatism.

Astigmatism; Vector analysis; Femtosecond laser; Rotation; Decentration