Thermomechanical Behavior of Collagen-Cross-Linked Porcine CorneaSpoerl E. · Wollensak G. · Dittert D.-D. · Seiler T.
Departments of aOphthalmology and bPathology, Universitätsklinikum CGC, Dresden, Germany; cInstitut für Refraktive und okuloplastische Chirurgie (IROC), Zürich, Switzerland
Purpose: Collagen cross-linking using combined riboflavin/UVA treatment has been shown to increase the biomechanical rigidity of the cornea and has been used successfully for the treatment of progressive keratoconus. From morphological and biochemical investigations, a different degree of cross-linking for the anterior and posterior stroma by the treatment is suggested. The present study was undertaken to better evaluate this effect by testing the thermomechanical behavior. Methods: Ten 10 × 5 mm corneal strips from porcine cadaver eyes enucleated within 5 h post mortem were cross-linked using the photosensitizer riboflavin and UVA irradiation (370 nm, irradiance = 3 mW/cm2) for 30 min and compared to ten untreated corneal strips and ten corneal strips cross-linked with 0.1% glutaraldehyde. The temperature in a water bath was raised from 60 to 95°C with temperature increments of 1°C per minute. The hydrothermal shrinkage of the corneal strips was measured in 2.5°C steps using a micrometer. In addition, six 10-mm whole corneal buttons were cross-linked with riboflavin/UVA and immersed into water at 70 or 75°C. Results: The maximal hydrothermal shrinkage for the untreated control specimens and the posterior portion of the riboflavin/UVA-treated corneas was at 70°C, for the anterior portion of the cornea cross-linked by riboflavin/UVA at 75°C and for glutaraldehyde-cross-linked cornea at 90°C. In the cross-linked corneal buttons, a typical mushroom-like shape was observed at 70°C and a cylinder shape at 75°C. Conclusions: The different degree of collagen cross-linking in the corneal stroma after riboflavin/UVA treatment is reflected by the differences in the maximal shrinkage temperature of the anterior and posterior portion. Therefore, in the corneas cross-linked with riboflavin/UVA a higher shrinkage temperature was observed for the anterior portion of the cornea (75°C) compared to the posterior stroma (70°C) due to the higher degree of cross-linking of the anterior stroma. The anterior localization of the cross-linking effect is advantageous for the endothelium and for the preservation of the anterior corneal curvature.
PD Dr. Eberhard Spoerl
Department of Ophthalmology, Universitätsklinikum CGC
Fetscherstrasse 74, DE–01307 Dresden (Germany)
Tel. +49 351 458 3763, Fax +49 351 458 4335
Received: June 6, 2003
Accepted after revision: October 9, 2003
Number of Print Pages : 5
Number of Figures : 3, Number of Tables : 0, Number of References : 13
Ophthalmologica (International Journal of Ophthalmology)
Founded 1899 as ‘Zeitschrift für Augenheilkunde’ by H. Kuhnt and J. von Michel
Vol. 218, No. 2, Year 2004 (Cover Date: March-April 2004)
Journal Editor: Ch. Ohrloff, Frankfurt a.M.
ISSN: 0030–3755 (print), 1423–0267 (Online)
For additional information: http://www.karger.com/oph