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Aghapi mordovanakis, Larry Baitch; Subsurface Femto-Laser Photodisruption in the Sclera for the Creation of Presbyopic Implant Tunnels. Invest. Ophthalmol. Vis. Sci. 2013;54(15):4278.
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The PresVIEWTM procedure (Refocus Group, Dallas, TX) is a surgical ophthalmic procedure for the improvement of near visual acuity in presbyopes. In that procedure, a precision bladed device, scleratome, dissects the scleral tissue at a plane 400μm below the surface of the perilimbal sclera, resulting in a tunnel into which each of four PresVIEWTM Scleral Implants (PSI) are implanted per eye. Our studies seek to determine the feasibility of using laser sources similar to those used in currently-approved refractive femtolaser platforms, for development of a laser-based method for the creation of precise and predictable PSI tunnels.
Scleral tissue is highly scattering for the near-infrared (NIR) wavelengths (1030-1065nm) employed by femtosecond refractive lasers. Our approach was to focus femtosecond laser pulses below the surface of porcine scleral sections to induce precise disruption about the laser focal plane. We created tunnels by raster-scanning the focused laser beam while translating the tissue along the tunnel length. We investigated the ablation efficacy at various depths (down to 400μm) under different laser parameters (shot pattern, pulse energy and repetition rate, lens numerical aperture). After laser exposure, scleral tissue samples were subjected to: 1) histological assessment to quantify uniformity of tunnel depth and collateral damage to cells; 2) optical microscopy of the scleral tissue, cleared with a 40% glucose solution after laser irradiation; and 3) mechanical instrument probing to simulate the insertion of PSI implants.
Optical microscopy of cleared sclera showed explicit subsurface disruption when irradiated with microjoule-energy pulses at 1030nm wavelength. The efficacy of tissue separation was demonstrated by inserting a 1mm-wide blunt probe along tunnels of 3-4mm length. Histological assessment continued to show improvement in accuracy and consistency of the ablated tissue plane as the irradiation parameters were refined.
Given the challenges that scleral tissue presents as an optical medium, our preliminary parametric trials of scleral subsurface femtosecond laser ablation on ex-vivo porcine are encouraging. These early results suggest that currently available refractive femtolaser platforms might be adapted for the creation of PSI tunnels. In-vivo animal experiments are necessary to assess the clinical viability of the procedure.
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