June 2013
Volume 54, Issue 15
Free
ARVO Annual Meeting Abstract  |   June 2013
Corneal biomechanical properties in corneal collagen cross-linking (CXL) at high fluences
Author Affiliations & Notes
  • Arthur Hammer
    Ophthalmology, Geneva University Hospitals, Geneva, Switzerland
  • Olivier Richoz
    Ophthalmology, Geneva University Hospitals, Geneva, Switzerland
  • David Tabibian
    Ophthalmology, Geneva University Hospitals, Geneva, Switzerland
  • Florence Hoogewoud
    Ophthalmology, Geneva University Hospitals, Geneva, Switzerland
  • Farhad Hafezi
    Ophthalmology, Geneva University Hospitals, Geneva, Switzerland
    Ophthalmology, Doheny Eye Institute, Keck school of medicine USC, Los Angeles, CA
Investigative Ophthalmology & Visual Science June 2013, Vol.54, 4073. doi:
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    • Get Citation

      Arthur Hammer, Olivier Richoz, David Tabibian, Florence Hoogewoud, Farhad Hafezi; Corneal biomechanical properties in corneal collagen cross-linking (CXL) at high fluences. Invest. Ophthalmol. Vis. Sci. 2013;54(15):4073.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose: The current intensity/irradiation profile for collagen cross-linking (3 mW/cm2 for 30 minutes) has been in clinical use since 1999 in a multitude of studies. Lately, different irradiation profiles have emerged, with the intention to lower irradiation time while maintaining the total energy dose (Bunsen-Roscoe law). Little is known whether these modified irradiation profiles will lead to the same increase in biomechanical stiffness observed in the original protocol.

Methods: We investigated the biomechanical properties in ex vivo porcine corneas at 3 (n = 10), 9 (n = 10), and 18 (N = 12) mW/cm2 for various time periods (30, 10, 5 minutes), while maintaining the total energy dose identical (Bunsen-Roscoe law). Prior to irradiation, riboflavin 0.1% was applied on the de-epithelialized cornea for 20 minutes. Controls (n = 11) were treated similarly, but without UV-A irradiation. Stress-strain measurements were performed using an extensometer (Zwick Roell, Model ZO.05, Zwick GmbH & Co. KG, Ulm, Germany).

Results: We observed a decrease in Young’s modulus with increasing UV-A intensity (fluence). Young’s modulus at 4 %, 6 %, 8 % and 10 % strain at 3 mW/cm2 was 1.66 N, 0.75 N, 0.44 N and 0.29 N respectively. At 9 mW/cm2, we measured 1.52 N, 0.7 N, 0.39 N and 0.24 N, whereas at 18 mW/cm2, we detected 1.2 N, 0.57 N, 0.33 N and 0.21 N for 18 mW. Controls showed 0.72 N, 0.37 N, 0.37 N and 0.16 N.

Conclusions: The increase in biomechanical strength of the porcine cornea following CXL diminishes with increasing fluence/decreasing irradiation time, even if the total energy dose is maintained. The generation of chemical bonds during cross-linking is an oxygen-dependent process that depends on intra-stromal oxygen concentration. Oxygen diffusion capacity is limited within the stroma and the increased oxygen consumption at higher fluence/lower irradiation time might become a limiting factor for cross-linking, leading to the observed decrease in treatment efficacy.

Keywords: 480 cornea: basic science • 574 keratoconus  
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