Abstract

P 235

Corneal flap cuts using the 200 kHz wavelight ultraflap femtosecond laser: accuracy, morphology, and histopathology

Ramin Khoramnia1, Chris Patrick Lohmann1, Christian Wüllner2, Christof Donitzky2, Christoph Winkler von Mohrenfels1
1Augenklinik, Klinikum rechts der Isar, Technische Universität München, München; 2WaveLight AG, Erlangen

Objective
High precision in corneal flap cutting is of major importance in LASIK surgery. Especially the creation of very thin flaps has lately gained importance for Sub-Bowman’s keratomileusis. Presently, there is a trend towards faster femtosecond lasers that produce flaps more quickly. In this study, flaps created with a 200 kHz femtosecond laser were evaluated concerning their cut accuracy, morphology, and histopathology.
Methods
Femtosecond laser flap cutting was performed on thirty-six porcine cadaver eyes using the prototype 200 kHz femtosecond laser WaveLight UltraFlap (WaveLight, Erlangen, Germany). The eyes were assigned to three different thickness groups, with 100, 130, or 180 µm cut depth, respectively. Furthermore, flap diameters were varied (8.0, 8.5, 9.0, and 9.5 mm). After flap creation, all eyes were examined thoroughly in order to evaluate the accuracy of the cut and to detect potential damages. Flap diameters were determined using a sliding caliper.  Flap thicknesses were measured with a micrometer. In addition, flaps were created for further histopathologic examination.
Results
All flaps could be created easily without any complications. Flap thickness was in mean 96.33±7.45 µm (intended: 100 µm), 134.67±4.96 µm (intended: 130 µm), and 174.59±9.35 µm (intended: 180 µm), respectively. There was a good accuracy in all three groups. Regarding the flap diameter, the mean values were 8.03±0.15 mm (intended diameter: 8.0 mm), 8.56±0.10 mm (intended diameter: 8.5 mm), 9.09±0.10 mm (intended diameter: 9.0 mm), and 9.54±0.15 mm (intended diameter: 9.5 mm), respectively. There was no significant difference between the four different diameters concerning the deviation between measured and attempted diameters. Histopathologic examination revealed very little to almost no changes in the corneal structure.
Conclusions
Flap creation could be performed easily without any complications. Accuracy and morphology of the cuts were very reliable and precise. Histopathologic examination showed a smooth cut with very little to almost no changes in the structure of the corneal stroma. Therefore, the 200 kHz femtosecond laser seems to be a promising new device in refractive surgery. The visual outcome is yet to be determined.

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