LAMELLAR REFRACTIVE SURGERY WITH SCANNED INTRASTROMAL PICOSECOND AND FEMTOSECOND LASER PURSES IN ANIMAL EYES

PURPOSE: To evaluate the use of scanned intrastromal picosecond and fe mtosecond laser pulses in lamellar refractive surgical procedures. MET HODS: Intrastromal corneal photodisruption was performed in fresh porc ine and primate cadaver eyes with a solid-state femtosecond laser. Las er pulses were focused 150 to 200 mu m below the epithelial surface an d scanned in a spiral pattern to create a plane. A flap was made by sc anning an are pattern from the plane of the spiral to the surface of t he cornea. Tissue plane separation was graded using a standard scale, while internal surfaces were analyzed by scanning electron microscopy. Comparison was made to a picosecond laser system using the same deliv ery system device. Creation of a stromal lenticule for in situ keratom ileusis was also demonstrated and compared with both laser systems, RE SULTS: For femtosecond pulses, tissue separation was achieved best wit h pulse energies from 4 to 8 mu J and spot separations from 10-15 mu m . Picosecond pulses accomplished less complete separations with pulse energies of 25 mu J and spot separations from 10 to 20 mu m. Surface q uality corresponded to dissection results, with high-grade dissections resulting in a smooth surface appearance, versus a more irregular sur face for low-grade dissections. Although high-grade dissections could be created with picosecond pulses (with optimal parameters) in ex vivo porcine eyes, only femtosecond parameters produced similar results in ex vivo primate eyes, CONCLUSION: In contrast to previous attempts us ing picosecond lasers which require additional mechanical dissection, high precision lamellar refractive surgery may be practical with femto second laser pulses.