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 crosslinking (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 (∆, 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 ∆spherical aberration, whereas mMPS significantly correlated with ∆eccentricity. In Group 2, hMPS significantly correlated with K2, Kmax, I-S index, and ∆coma, and hMPSy significantly correlated with I-S index and ∆coma. The mMPS significantly correlated with ∆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.