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Robert Herber, Mathew Francis, Eberhard Spoerl, Lutz E Pillunat, Frederik Raiskup, Abhijit Sinha Roy; Establishing the link between waveform derived corneal stiffness and ex vivo derived corneal elastic modulus: A prospective study with air-puff applanation of porcine eyes. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1395.
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© ARVO (1962-2015); The Authors (2016-present)
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 stress-strain measurement in ex-vivo porcine eyes.
Twenty fresh enucleated by slaughterhouse and de-epithelialized porcine eyes were soaked in 0.1 % riboflavin solution including 10 % dextran for 10 min. Following, a dynamic Scheimpflug based tonometry (Corvis ST, Oculus, Wetzlar, Germany) was performed in all eyes, plugging them with a needle connected to a manometer for adjusting a continuous IOP. In group 1, 10 eyes were cross-linked using the CCL Vario (10 min, 9 mW/cm2, diameter: 11 mm). Group 2 contained 10 eyes as controls without UV light irradiance. Corneal strips with a defined width of 5 mm and length of 14 mm were separated from all eyes with a double-bladed scalpel. Stress-strain measurements were performed with a microcomputer-controlled biomaterial tester (Minimat, Rheometric Scientific GmbH). The corneal tissue was clamped with a distance of 7 mm between the holders. Dynamic corneal response (DCR) parameters of Corvis ST were exported using the research software (1.03b1716). Corneal stiffness parameter (kc[mean] and kc[linear]) were calculated from blinded raw data of Corvis ST.
Regarding DCR parameters, 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 +10.7±0,9 N/m (P = 0.008) and +10.6±0.9 N/m (P = 0.005), respectively. In stress-strain measurements, cross-linked corneas showed significant higher rigidity compared to controls in stress at 2% and 4% by factor 1.53 (P = 0,013) and 1.89 (P = 0,001), respectively.
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.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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