Abstract

SA.05.03

Influence of collagen cross-linking with Riboflavin and UV-A on therapeutic and refractive excimer laser surgery

Keller S., Kampik D., Schlunck G., Haigis W., Geerling G.
Department of Ophthalmology, University of Wuerzburg

Objective: Cross-linking the corneal collagen with Riboflavin and UV-A-light increases corneal rigidity. This new therapeutic modality can stop progression of keratoconus. The Excimer-Laser can be used for therapeutic and refractive corneal surgery, i. e. corneal transplantation. The aim of this study was to determine whether the cross linking procedure may influence the ablation rate, flap thickness and the result of therapeutic or refractive corneal procedures.
Methods: In enucleated pig eyes the corneal epithelium was removed 2-9 hours post mortem and cross-linking with Riboflavin and UV-A was performed. The intraocular pressure was kept at 20 mm Hg throughout the experiments. An Excimer laser (Esiris, Schwindt) and a Carriazo-Pendular microkeratome with a 150 µm head were used to treat cross-linked (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.
Results: A PTK of an intended depth of 500 µm resulted in an ablation of 481.7 µm in group I and in group II 481.6 µm II (p=0.99). Mean corneal flap-thickness after a150 µm microkeratome cut was 109.9 µm in group I and 79.7 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 18.3 D ±1.6 D (18.4 D ±2.3 D),11.0 D ±2.2 D (10.2 D ±2.8 D) and 4.7 D ±2.2 D (5.9 D ±1.9 D) in group I (II). Although there was a trend for cross-linked corneas towards a lower refractive result, none of the differences observed was significant.
Conclusions: Collagen cross-linking with Riboflavin and UV-A in porcine eyes resulted in significantly higher flap thickness. Therapeutic and refractive outcome of Excimer-Laser ablation however, was not affected even with extreme ablations. In cross-linked corneas laser parameters may not require alteration.

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