Results Of Intrastromal Corneal Ring Segment Implanted Alone Or Combined With Same-Day Corneal Crosslinking And Their Correlation With Preoperative Corneal Biomechanical Strain From Finite Element Analysis

Purpose: To compare the results of intrastromal corneal ring segment (ICRS) alone or combined with same-day corneal cross linking (CXL) and investigate the relationship of preoperative corneal biomechanics data on the outcomes.Setting: Department of Ophthalmology of Federal University of Parana.Design: Prospective nonrandomized interventional comparative study.Methods: Forty-nine eyes of 44 keratoconus patients underwent ICRS only (n = 27, Group 1) or same day ICRS+CXL (n = 22, Group 2) and were followed up for at least 24 months. Visual acuity and preoperative and postoperative tomographic variables were compared between groups. Tomographic data were obtained with a dual Scheimpflug analyzer, and eye specific finite-element models were used to derive 3 variables related to preoperative biomechanical strain (maximum principal strain [MPS]): mean MPS (mMPS), highest local MPS (hMPS), and position of the hMPS (hMPSx and hMPSy). The relationship between preoperative strain data and the change (Delta, difference between postoperative and preoperative data) in tomographic parameters was also investigated.Results: Steepest (K2) and maximum keratometry (Kmax), inferior-superior (I-S) index, coma, and cone location magnitude index (CLMI) significantly improved in both groups. Corrected distance visual acuity was significantly better after ICRS alone (P = .03), whereas corneal asymmetry measured through the I-S index was better after CXL+ICRS (P = .04). In Group 1, hMPSy significantly correlated with K2, tomographical cylinder, mean keratometry, and Delta spherical aberration, whereas mMPS significantly correlated with Delta eccentricity. In Group 2, hMPS significantly correlated with K2, Kmax, I-S index, and Delta coma, and hMPSy significantly correlated with I-S index and Delta coma. The mMPS significantly correlated with Delta CLMI.Conclusions ICRS alone seems to be the most suitable option to improve visual acuity, whereas combined ICRS+CXL provided better corneal regularizing results. Preoperative peak strain (hMPS) was predictive of the extent of regularization and flattening after ICRS+CXL. Copyright (c) 2020 Published by Wolters Kluwer on behalf of ASCRS and ESCRS