Femtosecond laser photodisruption of human trabecular meshwork: an in vitro study

The goal of this in vitro study was to test the feasibility of using femtosecond (fsec) laser pulses to fistulize the human trabecular meshwork (TM), and to determine the minimum exposure time and energy dosage needed to create an ablation channel. Corneo-scleral rims were obtained from tissue used for penetrating keratoplasty. Four millimeter tissue strips hydrated in Optisol-GS were used to create partial thickness fistulas in the human TM by focusing a Ti:Sapphire laser beam (45 fsec, 1 kHz, 800 nm) with various pulse energies (7.2 and 14.4 microJ) and exposure times (0.25, 0.5, 1, and 2 sec) on the inner surface of the TM. Two-photon images of the lesions were obtained with a multiphoton microscope, using an ultrafast Ti:Sapphire light source. In addition, sections of fixed tissue were examined by light microscopy. Diameters and lengths of the lesions were determined from the hematoxylin and eosin (H&E) stained sections, and the collagen structure surrounding the lesion was evaluated from the two-photon images. All selected time points (except for 0.25 sec) and energies achieved the desired photodisruption of the TM. Incisions created with 0.5 sec/14.4 microJ irradiation appeared to be the most suitable because they were able to achieve consistent full thickness trabecular ablation. Incisions created at 1 sec /14.4 microJ/pulse and 2 sec/14.4 microJ/pulse were deeper than those at shorter time points with the same pulse energy. Longer exposure times and higher pulse energies were usually more variable and associated with deeper and larger incisions and slight collateral damage. Our results indicate that, with appropriate exposure time and pulse energy, fsec photodisruption can be employed to create lesions in the human TM without damaging the surrounding tissues. This study demonstrates that fsec laser treatments may have future potential for the surgical treatment of glaucoma.