97th DOG Annual Meeting 1999
OPTIMIZING THE LASER PARAMETERS FOR INTRASTROMAL CUTTING BY ULTRASHORT LASER PULSES
A. Heisterkamp1,2, G. Maatz1,2, H. Lubatschowski 1,2, W. Ertmer2, H. Welling1
Applying ultrashort laser pulses with a duration of some 100 femtoseconds, the creation of highly accurate cuts inside the cornea is viable. In comparison to longer laser pulses, ultrashort pulses have the advantage that the required energies are considerably lower. This minimizes thermal and mechanical side effects, as well as the transmitted energy dose on the retina.
This method of intrastromal photodisruption allows a precise energy deposition in the laser focus and, thus, an exact cut with reduced thermal and mechanical damage to the surrounding tissue.
With a Ti:Sapphire femtosecond laser system, the cutting effects of fs-laser pulses were investigated in corneal stroma. The irradiated samples were examined by light and electron microscopy in order to determine quality and reproducibility of the cut, as well as the degree of precision which can be achieved. In particular, different scanning algorithms were applied and analysed with respect to the resulting cut quality.
The extent of mechanical stress to the surrounding tissue after fs-photodisruption could be assessed by pressure measurements with broad band acoustic transducers, and by flash photography. In addition, the energy transmitted onto the retina was determined to be sufficiently low to eliminate the possibility of damage.
Side effects with fs-keratomileusis, especially thermal and mechanical stress to the surrounding tissue, are comparable to applications of excimer lasers. Therefore, this method appears to be highly promising for intrastromal refractive surgery.
1 Laser Zentrum Hannover e.V. Hollerithallee 8, D-30419 Hannover
2 Institut für Quantenoptik, Universität Hannover, Am Welfengarten 1,