Safety evaluation of femtosecond lentotomy on the porcine lens by optical measurement with 50-femtosecond laser pulses.

BACKGROUND AND OBJECTIVE The optimized parameters of femtosecond (fs) lentotomy, an innovative strategy for presbyopia, have been further discussed regarding the safety of the procedure for eyeballs. This article's aim was to prove the safety and feasibility of the fs lentotomy procedure with 50-fs laser pulses. STUDY DESIGN/MATERIALS AND METHODS This was an experimental study in which the safety of fs lentotomy by optical measurement was tested. The experiment was performed on 49 porcine crystalline lenses by 50-fs laser pulses at a central wavelength of 800 nm and scanning focusing optics with a numerical aperture (NA) of 0.125. The input pulse energy was in the range of 0.35 μJ to 0.65 μJ. The transmitted energy throughout the eyeball was measured through a hole in the back wall of the eyeball by a power meter. The transmittance and peak power density (PPD) on the cornea, lens, and retina were illustrated. The laser cutting quality of 50-fs laser pulses on the crystalline lens were assessed, and the theoretical safety of such a procedure for the cornea, lens, and retina was evaluated. RESULTS A sharp cut without noticeable large bubbles was obtained with 0.35 μJ pulse energy under the optical system for which the NA was 0.125. The transmittance of the whole eyeball was measured to be 69% to 75% under 0.35 μJ to 0.65 μJ incident laser energy. The threshold of PPD for photodisruption on the crystalline lens, retina, and cornea was measured to be in the magnitude of 10(13)  W/cm(2) , 10(8)  W/cm(2) , and 10(9)  W/cm(2) , respectively. CONCLUSIONS The cutting quality in this experiment implied the feasibility of the 50-fs laser in fs lentotomy; the pulse energy for fs lentotomy descended from microjoules to hundreds of nanojoules, and the PPD on the cornea and retina during the procedure decreased further, both of which illustrated the safety of such an optical design and the parameters during fs lentotomy for the eyeball.