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

Abstract

Introduction We aimed to measure the relationship of location between the tear film center (TFC) and corneal vertex (CV) following small incision lenticule extraction (SMILE). Methods A total of 100 consecutive patients (100 eyes) who underwent the SMILE procedure were included. Screen captures of intraoperative videos and pupillary offset were analyzed. Location was compared using a vector plot for the two reference points. Results The arithmetic values for the distance from the pupil center (PC) were almost identical between the TFC and CV ( P = 0.118). The intraclass correlation coefficient (ICC) for the measures of distance from the CV and TFC to the PC was 0.659. The mean vector and standard deviation ellipse showed similar directional tendencies for both reference points. No significant difference was observed in the arithmetic values of decentration from the TFC and from the CV ( P = 0.056). The ICC for the measures of decentration from the TFC and from the CV was 0.768. The difference in the distance from the PC was significant for the tear film mark (TFM) decentration group ( P = 0.002, ICC = .480), while the difference in decentration was significant for the TFM centration group ( P = 0 .000, ICC = 0.230). Conclusions The location of the CV in each eye could be simulated by the TFC. Furthermore, TFM decentered displacement could indicate optical zone decentered displacement.

Methods of Corneal Vertex Centration and Evaluation of Effective Optical Zone in Small Incision Lenticule Extraction

“…Huang et al [26] even found that the decentration of EOZ centroid in both eyes was different (the right eye shifted superior while the left eye shifted to the nasal side), although both eyes were centered on the CV by the TFM method. The latest research showed that the TFM center can simulate the position of the CV accurately and indicated that the decentration of EOZ after the operation can be predicted in advance by observing the change of the TFM center during the operation [47]. The differences between the above studies on the relationship between centration methods and the EOZ may be attributed to differences in patients’ refractive status, kappa angle, and postoperative decentration measurement methods.…”