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Establishing the link between waveform-derived corneal stiffness and stress-strain extensometry-derived corneal stiffness: a prospective study with air-puff applanation of ex vivo porcine eyes

Poster Details

First Author: R.Herber GERMANY

Co Author(s):    M. Francis   E. Spoerl   L. Pillunat   F. Raiskup   A. Roy        

Abstract Details


Corneal cross-linking (CXL) is the most common treatment in progressive keratoconus to stiffen the ectatic cornea. Biomechanical effects of CXL are expected to validate by new corneal stiffness parameters derived from dynamic Scheimpflug-based tonometry and tensile stiffness derived from stress-strain extensometry in ex-vivo porcine eyes.


Department of Ophthalmology, Technical University of Dresden, Dresden, Germany; Narayana Nethralaya Foundation, Bangalore, India


Thirty fresh enucleated and de-epithelialized porcine eyes were soaked in 0.1%-riboflavin solution including 10% dextran for 10min. Eyes were separated in two groups. Group 1 included 15 eyes as controls. In group 2, 15 eyes were cross-linked using CCL Vario (10 min, 9 mW/cm²). Dynamic Scheimpflug-based tonometry (CST, Corvis ST, Oculus, Wetzlar, Germany) was performed in all eyes. Following, corneal strips were extracted by a double-bladed scalpel (5x14mm) and used for stress-strain measurements (Minimat, Rheometric Scientific GmbH). Dynamic corneal response (DCR) parameters of CST were analyzed. Corneal stiffness parameter (kc[mean] and kc[linear]) were derived from CST raw data.


The cross-linked corneas showed a significant increase in biomechanical corrected IOP, SPA1 and significantly reduced deformation amplitude max, peak distance, max inverse radius and integrated radius after CXL (P<0.05). Kc[mean] and Kc[linear] significantly increased by +10.9±10.3N/m (P=0.001) and +10.7±9.1N/m (P < 0.001), respectively. Tensile corneal stiffness (kc[ts]) derived from stress-strain measurements at 4% strain were significantly higher in cross-linked tissue compared to controls by factor 2.21 (P<0.001). Regarding all eyes, a significant correlation was observed between kc[ts] and kc[mean] (r=0.543; P=0.002) as well kc[linear] (r=0.505; P=0.004), but not in subgroups.


Stiffening effects of CXL could be demonstrated with different measuring techniques in an experimental set-up. Several DCR parameters and especially new developed stiffness parameters Kc[mean] and Kc[linear] verify corneal stiffening after CXL on a porcine eye globes and have the ability to perform also in vivo.

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