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G. Geerling, S. Keller, G. Schlunck, W. Haigis, D. Kampik; Influence of Corneal Collagen Crosslinking With Riboflavin and UV-A (CXL) on Therapeutic and Refractive Excimer Laser Surgery. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3917.
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Crosslinking the corneal collagen with riboflavin and UV-A irradiation (CXL) increases corneal rigidity. This new therapeutic modality can stop progression of keratoconus. The Excimer laser can be used for refractive and therapeutic corneal surgery, i.e. corneal transplantation. The aim of this study was to determine whether the crosslinking procedure may influence the ablation rate, flap thickness and refractive results of therapeutic or refractive corneal procedures.
In enucleated porcine eyes the corneal epithelium was removed 2-9 hours post mortem and crosslinking with riboflavin and UV-A was performed. The intraocular pressure was kept at 20 mm Hg throughout the experiments. An Excimer laser (Esiris, Schwindt, Germany) and a Carriazo-Pendular microkeratome (Schwindt, Germany) with a 150 µm head were used to treat crosslinked (group I) and normal (group II) corneas (n=10, each group). PTK was performed with a diameter of 6 mm in steps of 50 µm until perforation into the anterior chamber. LASIK was performed with 170 µm depth of ablation at 4, 6, or 8 mm diameter. Corneal thickness and refraction was measured before, during and after ablation by means of optical coherence tomography and Placido based topography.
PTK: Each intended 50µm-step resulted in an ablation of 45,3 µm ± 12,5 µm per step in group I and 45,2 µm ± 11,0 µm in group II (p=0.90). LASIK: Mean corneal flap thickness after a 150 µm microkeratome cut was 98,8 µm ± 26,0 µm in group I and 68,8 µm ± 30,0 µm in group II (p<0.01). Mean change of corneal refraction with an ablation of 170 µm for an optical zone of 4, 6 and 8 mm was 17,9 D ± 2,2 D (19,9 D ± 2,5 D),9,7 D ± 2,1 D (11,3 D ± 2,3 D) and 4,9 D ± 1,3 D (6,3 D ± 1.8 D) in group I (II). The flap thickness and the refractive results in each ablation diameter showed significant differences in the results between the crosslinked and untreated group. Concerning the ablation rate, the differences observed have not been significant.
Collagen crosslinking with Riboflavin and UV-A in porcine eyes resulted in significantly higher flap thickness. Furthermore, the refractive outcome of Excimer laser ablation is reduced significantly. This might be due to a higher stiffness and more compact collagen fibers of the crosslinked cornea. This ex-vivo study potentially suggests an adjustment of the microceratome and laser parameters for Excimer laser treatments after CXL.
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