CORNEAL SURFACE ROUGHNESS AFTER EXCIMER LASER PRK DEPENDING ON BEAM SHAPING SYSTEM
B. Müller1, St. Schründer1, K. Nordwald1, Th. Boeck2, T. Walkow1
Introduction: The corneal surface roughness is regarded as a parameter influencing epithelial and stromal wound healing after Excimer laser PRK for correction of myopia. Each laser beam shaping system creates a specific ablation pattern and roughness onto the corneal surface. The roughness of the cornea has not been quantified in a biological model.
Method: Excimer Laser PRK for correction of myopia of -3, -6, -9 D were performed on 10 porcine eyes in each group using the Schwind Keratom and the Aesculap Meditec MEL 60. The Schwind Keratom is a "broad area" laser using a band mask for beam shaping. In contrast the Meditec MEL 60 is a slit scanning laser with an handhold eye fixated constricting iris mask for beam shaping. A silicon replica conserving the corneal roughness was obtained immediately after PRK procedure. The roughness was measured with the UBM Microfocus a confocal topometry system. A group of 10 porcine eyes with epithelium removed served as a control group.
Results: The mean surface roughness of the control group was 0.75 µm (SD=0,02). The Schwind Keratom created centrally after correction of -3, -6, -9 D a mean surface roughness of 0.86µm (0.06), 1.16 µm (0.11) and 1.15 (0.12), respectively. The Meditec MEL 60 induced centrally a mean surface roughness of 0.96 µm (0.09), 1.51 µm (0.11) and 1.63 µm (0.13) for correction of -3, -6,-9 D respectively. The Meditec MEL 60 created a rougher central surface in comparison with the Schwind Keratom because of the higher ablation depth to achievc the same correction The induced relative roughness per pm of ablation depth for correction of -3, -6, -9 D with the Schwind Keratom was 2.5% (SD=0.17), 1.8% (0.16) and 1.7% (0.18) respectively. The Meditec MEL 60 induced a relative surface roughness per pm ablation depth of 2.4 % (0.23) for -3 D, 1.9% (0.14) for -6 D and 2.1% (0.16) for -9 D.
Conclusion: The centrally measured mean surface roughness increases proportionally with higher ablation depth. Both laser beam shaping systems induced an equal relative roughness per pm ablation depth. The relative roughness per pm ablation depth appears to decrease with higher corrections..
1Department of Ophthalmology, Charite, Campus Virchow-Hospital, Humboldt- University Berlin
2Institute for Crystallography, Berlin