Comparison of the Distribution of Lenticule Decentration Following SMILE by Pupil Center or Tear Film Mark Centration

Abstract

PURPOSE: To investigate lenticule decentration following small incision lenticule extraction (SMILE) via the pupil center or tear film mark centration method and compare induction of corneal higher order aberrations (HOAs) between the two methods. METHODS: This study analyzed decentration values obtained from tangential topography difference maps of 100 eyes (100 patients) undergoing SMILE with the pupil center (n = 50) or tear film mark (n = 50) centration method. Total HOAs and component aberrations were measured preoperatively and 6 months postoperatively. Relationships between the magnitudes of decentration and induced corneal HOAs were assessed. RESULTS: Both vertical and total decentered displacement were significantly different ( P < .001) between the two centration groups. A significant relationship between the preoperative pupillary offset and decentration was noted in the pupil center group ( P < .001), but not in the tear film mark group ( P = .530). Significantly greater induction of total HOAs, coma, and vertical coma (all P < .001), as well as horizontal coma ( P = .001) and spherical aberration ( P = .023), were observed in the pupil center group. Association between the total decentered displacement and induced total HOAs ( P < .001), as well as all other significantly increased phenomena, was also significant in the pupil center group. Differences in decentered displacement and induced corneal HOAs were significant for preoperative pupillary offset (angle kappa) greater than 200 µm, but not for angle kappa less than 200 µm. CONCLUSIONS: SMILE with tear film mark centration can yield improved treatment centration and less induction of total HOAs, coma, and spherical aberrations. [ J Refract Surg . 2020;36(4):239–246.]

Effect of keratometric astigmatism on visual outcomes following small incision lenticule extraction

“…SMILE procedures were performed as described previously with the VisuMax femtosecond laser system (Carl Zeiss Meditec AG, Germany) ( 7 ). To eliminate the influence of cyclotorsion in astigmatism correction, we have compensated for it by rotating the patient's head ( 8 ).…”

Relationship of Location Between Tear Film Center and Corneal Vertex Following Small-Incision Lenticule Extraction

“…A total of 100 consecutive patients (100 eyes) were included in this retrospective observational study. Patients were classified into group I (tear film mark centration group) or group II (tear film mark decentration group) based on an intraoperative decentration from the TFC average of 0.20 mm [ 10 ]. Demographic data are presented in Table 1 , and visual outcomes are shown in Fig.…”

“…Before vacuum aspiration, the cyclotorsion degree was adjusted by slightly rotating the patient’s head so that the horizontal reticule of the microscope overlapped with the cornea reference points (3 and 9 o’clock meridian) [ 12 ]. The tear film center was used for centering as described in our previous work [ 10 ]. After final confirmation that the green light was coincident with the tear film center (tear film mark was concentric with the margin of the cone), suction was initiated.…”

“…Decentration from the TFC was calculated using d = . The measurement of optical zone decentration was introduced in our recently published study [ 10 ]. The tangential curvature difference map displayed the (0, 0) point as the CV and a coordinate ( x , y ) in millimeters for optical zone centration relative to the (0, 0) point.…”

“…However, cyclotorsion and instability affect the suitability of the PC as a primary choice for locating the CV [ 7 – 9 ]. Our previous study demonstrated that the tear film mark (TFM) could be used for centering in SMILE surgery [ 10 ]. At the moment of contact between the curved contact glass and the maximum elevation point of the cornea, a meniscus tear film mark appears in the position of the CV in the coaxially fixating eye [ 11 ].…”