Biomechanical and morphological corneal response to placement of intrastromal corneal ring segments for keratoconus

To evaluate the biomechanical and morphological changes in keratoconic corneas after Intacs intrastromal corneal ring segment (ICRS) implantation.

Department of Ophthalmology, National Reference Center for Keratoconus, Bordeaux University, Bordeaux, France.

Keratoconic eyes were retrospectively analyzed after ICRS implantation; preoperative and 6-month postoperative evaluation were done using the Ocular Response Analyzer (ORA) and the Orbscan II topographer. Biomechanical parameters included corneal hysteresis (CH), the corneal resistance factor (CRF), and other parameters extracted from the signal curves. Morphological parameters included simulated keratometry and the cone location magnitude index from the axial map (aCLMI) and tangential map (tCLMI). Parameters were extracted using software designed to read and process topographic maps.

There were no significant differences between preoperatively and postoperatively in mean CH (7.7 mm Hg +/- 1.4 [SD] versus 7.4 +/- 1.4 mm Hg) or mean CRF (6.6 +/- 1.8 mm Hg versus 6.1 +/- 1.4 mm Hg). Only 2 ORA signal parameters were significantly different. Topographic parameters with significant decreases were minimum central keratometry (K) (mean change -5.8 +/- 2.9 diopters [D]) (P<.001), minimum central K (mean change -5.8 +/- 2.3 D) (P<.001), mean aCLMI (9.6 +/- 2.7 preoperatively versus 7.7 +/- 2.5 postoperatively) (P<.009), and mean tCLMI (18.9 +/- 2.8 versus 12.9 +/- 4.4) (P<.002). The only significant correlation between biomechanical and topographic parameters was postoperative ORA infrared signal peak 1 and postoperative aCLMI.

Intrastromal corneal ring implantation significantly decreased corneal curvature, with preoperative values predicting magnitude of change. However, it did not alter the viscoelastic biomechanical parameters of CH and CRF.