Human Optic Nerve Sheath Fenestration with the Free Electron Laser (FEL)

Abstract

Abstract: : Purpose: Our previous animal studies showed that the Amide II wavelength (6.45 µm) produced by the Free Electron Laser (FEL) could efficiently produce an optic nerve sheath fenestration. The reaction of the tissue was similar whether the fenestration was produced by the FEL or by a scissors. In order to determine if the technology safely could be applied to human surgery, we used blind human eyes during enucleation to compare the results of producing fenestrations with the FEL or a scissors. Methods: FDA approval, Vanderbilt Institutional Review Board approval, and individual patient consents were obtained for a series of 10 subjects. The FEL energy was transmitted to an accredited human operating room. After disinsertion of the medial rectus muscle, an optic nerve sheath fenestration (2 mm diameter) was made with either the FEL (6.45 µm, 325 µm spot size, 30 Hz, 3 mJ) through a hollow waveguide surgical probe or with a scissors. The excised sheath was removed with a microforceps. The enucleation was then completed. The optic nerve was dissected from the globe and fixed in 3% paraformaldehyde, 0.1% glutaraldehyde, and 0.2% picric acid (v/v). Sections were examined with H&E, and with antibodies to GFAP, S100ß, and vimentin to compare the 2 techniques. Results: Three circular passes with the FEL probe produced CSF release and an effective optic nerve sheath incision. Tissue glial responses using either the FEL or the scissors method were similar. No acute damage or thermal damage to the optic nerve was found with the FEL energy. Conclusions: FEL energy at 6.45 µm can be transmitted to an operating room and delivered to human ocular tissue through a hollow waveguide surgical probe. The FEL at 6.45 µm wavelength can efficiently produce an optic nerve sheath fenestration in blind human eyes without acute damage to the nerve. These subjects had normal amounts of CSF in the subarachnoid space, rather than the distended amounts present in pseudotumor cerebri that would theoretically offer even greater protection to the optic nerve from any infrared laser–tissue interaction during fenestration of the sheath. .

Keywords: pathology: human • microscopy: light/fluorescence/immunohistochemistry • laser