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Accelerating the biomechanical effect of the epi-off Dresden protocol
First Author: R. Abrishamchi SWITZERLAND
Co Author(s): H. Abdshahzadeh E. Torres-Netto N. Hafezi F. Hafezi
Corneal cross-linking (CXL) with riboflavin is an accepted method for halting the progression of ectasia. Accelerated protocols were suggested based on the Bunsen-Roscoe law, where a photochemical reaction should stay constant if the total energy is kept constant. By applying this law to CXL, irradiation time can be reduced by increasing the intensity, resulting in shorter procedures times. Knowing that the Bunsen-Roscoe law knows limitations regarding the biomechanical effect of CXL, the purpose of this study was to quantify corneal mechanical changes induced by optimized CXL procedures in terms of ultraviolet-A (UVA) fluence, intensity and exposure time.
The study was conducted at the Ocular Cell Biology Laboratory, Centre for Applied Biotechnology and Molecular Medicine at the University of Zurich (Switzerland).
Porcine eyes were divided into 5 groups and analysed. All samples were debrided of epithelia and soaked with riboflavin 0.1% solution. CXL was performed using 4 different epithelium-off protocols: standard 3mW/cm2 for 30 minutes (5.4J/cm2, S3/30-CXL), 9mW/cm2 for 13 minutes and 20 seconds (7.2J/cm2, A9/13-CXL), 9mW/cm2 for 10 minutes (5.4J/cm2, A9/10-CXL) and 18mW/cm2 for 6 minutes and 40 seconds (7.2J/cm2, A18/6-CXL). Control corneas were treated similarly, not irradiated. Youngﾒs modulus of 5-mm wide corneal strips was used as an indicator of corneal stiffness.
Hundred sixty-five porcine corneas were evaluated. All irradiated groups had significantly higher Youngﾒs modulus than controls (p < 0.05): with a stiffening effect of 152% (S3/30-CXL), 135% (A9/10-CXL), and 128% (A18/6-CXL). There was no significant difference between the Dresden protocol (S3/30-CXL) and the high-fluence accelerated A9/13-CXL protocol.
The Dresden protocol had the highest stiffening effect among our study groups. The biomechanical effect of CXL decreased gradually when accelerating while maintaining the Dresden protocol fluence of 5.4 J/cm2 (Bunsen-Roscoe law). However, once compensating for acceleration with a higher fluence of 7.2 J/cm2, we did not observe significant differences to the Dresden protocol. We therefore suggest a 13-minute irradiation with 9 mW/cm2 as an alternative to the Dresden protocol in epi-off CXL.
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