Application of ultrashort laser pulses for intrastromal refractive surgery

Background: Recently, laser systems have become available which generate ul trashort laser pulses with a duration of 100-200 femtoseconds (fs), By gene rating microplasmas inside the corneal stroma with fs pulses, it is possibl e to achieve a cutting effect inside the tissue while leaving the anterior layers intact. The energy threshold to generate a micro-plasma with fs puls es is some orders of magnitude lower than it is for picosecond or nanosecon d pulses. This results in a strong reduction of the thermal and mechanical damage of the surrounding tissue. Methods: With a titanium:sapphire fs laser system, the cutting effect on co rneal tissue from freshly enucleated porcine eye globes was investigated wi th differ ent pulse energies. The irradiated samples were examined by light and electron microscopy. The laser-induced pressure transients and the las er-induced bubble formation were analysed with a broadband acoustic transdu cer and by flash photography. Results: With fs laser pulses, the extent of thermal and mechanical damage of the adjacent tissue is in the order of 1 mu m or below and therefore com parable with the tissue alterations after ArF excimer laser ablation. Using pulse energies of approximately 1-2 mu J and a spot diameter of 5-10 mu m, intrastromal cuts can be performed very precisely in order to prepare corn eal flaps and lenticules. Conclusion: Femtosecond photodisruption has the potential to become an attr active tool for intrastromal refractive surgery.