Optimisation of the laser parameters for intrastromal incisions using ultrashort laser pulses

Background. With the assistance of ultrashort laser pulses (ca.200 fs pulse duration) it is possible to perform precise incisions inside the corneal s troma with a width of a few microns. The advantage of ultrashort pulses is that the required energy of a few micro-joules is more than an order of mag nitude lower compared with longer pulse durations, i.e. ps or ns pulses. Th erefore, the secondary effects, such as thermal and mechanical damage to th e surrounding tissue and the amount of radiation reaching the retina, are r educed. This method of intrastromal photodisruption allows a very well defi ned deposition of energy within the laser focus inside the corneal stroma,a ccompanied by minimal collateral damage. Methods. The possibilities of performing in; trastromal cuts using fs-laser pulses at a wavelength of 780 nm and pulse durations of 200 fs were studie d using a titanium-sapphire laser system. The treated tissue samples were a nalysed by light and scanning electron microscopy to determine incision qua lity reproducibility and achievable accuracy. The mechanical side effects o f fs-photo-disruption inside the surrounding tissue were analysed by pressu re measurements using pyroelectric transducers. Conclusion. The thermal and mechanical side-effects of this method are very low and comparable to the effects during excimer treatment. Therefore an a pplication of ultrashort laser pulses in refractive surgery appears to be a feasible alternative.