Application Of Tear Film Mark Centration In SMILE

Part I.Comparison of the Distribution of Lenticule Decentration Following SMILE by Pupil Center Centration or Tear Film Mark CentrationPurpose: To investigate lenticule decentration following small incision lenticule extraction(SMILE)via the pupil center(PC)or tear film mark(TFM)centration method and compare inductions 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 PC(n = 50)or TFM(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 PC group(P <.001),but not in the TFM 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 PC 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 PC group.Differences in decentered displacement and induced corneal HOAs were significant for preoperative pupillary offset(angle kappa)> 200 ?m,but not for angle kappa < 200 ?m.Conclusions: SMILE with TFM centration can yield improved treatment centration and smaller induction of total HOAs,coma,and spherical aberrations.Part II.Relationship of Location Between Tear Film Center and Corneal Vertex Following Small-Incision Lenticule ExtractionPurpose.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 pupil center(PC)were almost identical between the TFC and CV(P =.118).The total distance yielded an ICC of 0.659.The mean vector and standard deviation ellipse showed similar directional tendencies on both reference points.No significant difference in the arithmetic values of decentration from the TFC and from the CV was observed(P =.056).The total decentration yielded an ICC of 0.768.Difference in distance from PC was significant for TFM decentration group(P=.002,ICC=.480),while difference in decentration was significant for TFM centration group(P=.000,ICC=.230).Conclusions.The exact location of the CV in each eye could be simulated by the TFC.Furthermore,TFM decentrated displacement could indicate optical zone decentrated displacement.Part III.Impact of Keratometric Astigmatism on Optical Zone Decentration and Visual Outcomes in SMILE with Tear Film Mark CentrationPurpose: To investigate the effect of keratometric astigmatism on optical zone decentration and visual outcomes in small incision lenticule extraction(SMILE)with the tear film mark(TFM)centration method.Methods: 80 eyes undergoing SMILE for myopia correction were classified into two groups based on preoperative keratometric astigmatism.The associations of TFM characteristics and optical zone decentration with keratometric astigmatism were analyzed.The effect of optical zone decentration on vector components of astigmatic correction and induction of higher-order aberrations(HOAs)were assessed.Results: No significant difference was observed in the decentered distance between the high astigmatism(HA)and low astigmatism(LA)groups(HA: 0.17 ± 0.08 mm,LA: 0.16 ± 0.08 mm,P =.189).Regardless of TFM roundness,TFM decentration and decentered distance were not related to keratometric astigmatism in the HA group(P =.438,P =.395,P =.898)or the LA group(P =.319,P =.327,P =.487).There were no significant associations between the decentered distance and the vector components of astigmatic correction,or in induction of HOA in the HA group(P ?.294,P ?.112)or the LA group(P ?.323,P ?.080).Conclusions: Keratometric astigmatism did not affect tear film mark and treatment centration in SMILE.SMILE with TFM centration could achieve accurate centration and good visual quality even for patients with high astigmatism.