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Olivier Richoz, Samuel Arba Mosquera, Thomas Magnago, Farhad Hafezi; Determination of the excimer laser ablation rate in the porcine cornea after corneal collagen cross-linking (CXL). Invest. Ophthalmol. Vis. Sci. 2013;54(15):3714.
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A combination of collagen cross-linking (CXL) and customized surface ablation, performed sequentially, may be a promising means to correct for part of the irregular astigmatism in keratoconus and postoperative ectasia. Accordingly, surgeons will be confronted with patients that will present with previously cross-linked corneas requiring excimer laser ablation. Currently, the ablation rate per pulse in a cross-linked cornea is unknown, leading to potential inaccuracies in the amount of ablated tissue and postoperative result.
The excimer laser ablation rate of porcine corneas was analyzed using optic coherence pachymetry (OCP) ex vivo. Corneas were de-epithelialized and soaked with riboflavin 0.1% solution for 20 minutes. Riboflavin was washed off the corneal surface and corneas were cross-linked with 18 mW/cm2 for 5 minutes (CCL-365 Vario). Excimer laser ablation was performed (Schwind AMARIS 750S) to a total depth of 200 µm in four consecutive steps of 50 µm each. Controls were treated similarly, but were not irradiated with UV-A. 20 eyes were examined in each experimental condition.
The following depth-dependent differences were obtained: the first ablation from 0-50 µm microns showed no significant differences in ablation depth between cross-linked corneas and controls. For the three consecutive stromal ablations in deep stroma, we observed significantly less ablation in the cross-linked cornea when compared to non-cross-linked controls: 10.9 µm less for 50 - 99 µm (p=0.0001), 7.4 µm less for 100 - 149 µm (p=0.0003), and 7.2 µm less for 150 - 199 µm (p=0.003). Statistical analysis was performed using the Kruskal-Wallis test.
Following CXL, the excimer laser ablation rate in the cornea is significantly lower than in the untreated cornea and seems to be depth-dependent. Adaptation of the ablation rate and development of a nomogram for surface ablation in cross-linked ectatic corneas will be important to help improving best spectacle-corrected visual acuity.
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