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Howard Ying, Andrew Antoszyk, Thomas Hutchens, Arash Darafsheh, Amir Fardad, Nathaniel Fried, Vasily Astratov; Erbium:YAG Laser Scalpel with Novel Microsphere Chain Fiber Optic Tip for More Precise Vitreoretinal Surgery. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3305.
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To investigate the feasibility of developing an ultra-precise fiber optic delivery system for the Erbium:YAG laser that could ultimately be used in vitreoretinal surgery to transect/ablate intraocular proliferative membranes.
Novel fiber optic scalpels based on chains of coupled sapphire or ruby microspheres were developed. According to mathematical models, when these chains of spheres with optimal index of refraction (n=1.71) are assembled directly inside hollow waveguides (HWGs), they exhibit mode-filtering properties that lead to gradual reduction of the lateral dimensions of the periodically focused beams. The most compact beam is created in the vicinity of the surface of the end-sphere in the chain and has essentially zero focusing depth irrespective of the contacting tissue. Single, three, and five sphere chains were coupled to an Erbium:YAG laser (λ= 2.94 μm) and measured the full width at half-maximum (FWHM) of the central peak and ablation zones both in air and in contact with ophthalmic tissues, ex vivo.
Sapphire or ruby (n=1.71) microspheres showed reduction in the lateral dimension of the focused beam with three or five 300 µm diameter spheres, in agreement with the modeling. Fixed fiber experiments with a Scheaumann Erbium:YAG laser source showed FWHM beam diameters of ~ 9 µm using three-sphere chains. When coupled with a flexible, moving mid-IR fiber, the beam diameter increased to ~ 20µm in air. This delivery system coupled with a multimode, flash-lamp pumped, Er:YAG laser (Schwartz Electro-optics, 75 µs pulse width), cut corneal epithelium with an ablation crater depth and diameter of ~10 and ~25 μm, respectively, and a collateral thermal damage zone of ~30 μm. There was no evidence of sticking of the probe to the tissue or charring or other undesirable damage to the probe tip during the procedures.
The microsphere chain probe tip coupled with an Erbium:YAG laser provides precise tissue ablation in corneal epithelium, ex vivo. Potential application in vitreoretinal surgery warrants further investigation.
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