First Safety Study of Femtosecond Laser Photodisruption in Animal Lenses: Tissue Morphology and Cataractogenesis

Abstract

Abstract: : Purpose: Refractive surgery is beginning to focus on presbyopia correction. Photophaco-modulation is one attempt to restore accommodation by modifying lens tissue with a laser. Safety studies in animal lenses can determine the tissue effects and potential cataractogenesis. Methods: Six fresh porcine lenses and 6 living rabbit eyes are irradiated with a low energy femtosecond laser (Ti:Sapphire, 130 fsec). Several hundred thousand pulses with an energy of 1-4 µJ/pulse are applied to the lens epinucleus in one of two patterns: 3 concentric annuli or 8 radial slits. The rabbit eyes are treated according to ARVO guidelines, leaving one eye as a control. Both rabbit lenses are extracted and tested for light scatter with a low power He-Ne laser 3 months after the treatment, and then photographed and fixed for ultrastructure. Porcine eyes are fixed after lasing. Results: After the laser treatment, all lenses display bubbles which resolve with time. In the porcine eyes, the bubbles coalesce with a spacing pattern of > 9µm with pulse energy > 2 µJ applied. In the rabbit eyes, an energy of 1 µJ and spacing of 10µm is chosen for transcorneal delivery. Ultrastructurally, the porcine eyes demonstrate a 0.5µm electron dense border layer with adjacent normal lens architecture. After 3 months, the rabbit lenses demonstrate good transparency with only a fine optical distortion at the site of laser treatment. One rabbit, in both eyes, had cataract formation unrelated to the laser. In the other 5 rabbits, laser scanning studies reveal essentially identical values for the back vertex distance, sharpness of focus, and light scatter compared to the control. Conclusion: Femtosecond laser photodisruption of the ocular lens yields discrete lesions with a border zone of ~0.5µm, and bubbles which resolve with time. In the living animal eyes, no cataract formation can be found after 3 months, and there is a similar depth of focus and value of scatter when compared to fellow eyes. These preliminary results suggest that femtosecond laser can be safely used in modifying the paracentral lens nucleus/epinucleus for presbyopia correction.

Keywords: accommodation • refractive surgery: other technologies • refractive surgery: optical quality