Application Of Tomography Biomechanical Index In Preoperative Screening Of Early Keratoconus During Refractive Surgery

Objective:To evaluate the Tomographic Biomechanical Index(TBI)value in early corneal dilatation by observing the morphological and biomechanical changes of Laser in situ keratomileusis(LASIK)and femtosecond laser-assisted excimer laser in situ keratomileusis(FS-LASIK).Methods:The clinical records for 117 eyes of 72 patients who received LASIK or FS-LASIK in Shanxi Eye Hospital from January to December 2018 and had complete clinical data reviewed 3 years after surgery were reviewed and analyzed.According to the TBI,they were divided into two groups: normal group(TBI<0.29)and suspicious group(TBI≥0.29).In both groups,data were collected as follows: patient’s age,the Corneal diameter,the vision and refraction before and after surgery.Preoperative and postoperative parameters measured by Pentacam anterior segment analyzer and Corneal visualization Scheimpflug technology were both collected.Results:In both two groups,The height of the corneal posterior surface of the thinnest point before surgery were higher than 1 month after surgery(P<0.05).There was no statistically difference in the height of the corneal posterior surface of the thinnest point between 1month after surgery and 3 years after surgery(P≥0.05).And there was no statistically difference in the height of the corneal posterior surface of the thinnest point between the two groups before surgery,1 month after surgery and 3 years after surgery(P≥0.05).Deviation of average pachymetric progression(Dp),deviation of ARTmax(Da)and Pentacam Random Forest Index(PRFI)in the suspicious group were higher than those in the normal group before surgery and 3 years after surgery(P<0.05).Ambrósio’s Relational Thickness to the horizontal profile(ARTh)in the suspicious group were lower than the normal group before surgery and 3 years after surgery(P<0.05).Kmax and inferior-superior difference value(I-S value)in the suspicious group were higher than those in the normal group before surgery(P<0.05).There were no statistically differences in PRFI,I-S value,Kmax,Dp,Da and ARTh between the two groups before surgery and 3years after surgery(P≥0.05).TBI was taken as the dependent variable,and PRFI,I-S value,Dp,Da,ARTh ware taken as concomitant variables for multiple logistic regression analysis.The results showed that PRFI was associated with TBI value changes(β=2.717,OR=15.132,P=0.01).Conclusions:1.Patients with TBI≥0.29 and preoperative corneal posterior surface height of incomplete bridge or decreasing bridge showed no corneal dilation during 3-years follow-up after LASIK and FA-LASIK.2.When the height pattern of the posterior corneal surface was incomplete or decreased,TBI≥0.29 was mainly associated with PRFI.3.TBI value cannot only be used as a Biomechanical Index for screening early keratoconus.Change in other parameters should also be considered comprehensively.