Femtosecond transscleral photodisruption for the treatment of glaucoma.

Abstract

Approximately five million people worldwide are blind due to complications from glaucoma. Current surgical techniques often fail due to infection and scarring of the surface tissues, which is unavoidable using conventional lasers or surgical instruments. Subsurface incisions can be made using femtosecond lasers without damaging the overlying tissues that the beam has passed through. The purpose of this dissertation is to demonstrate a knife that can cut anywhere in the bulk of the sclera without damaging the tissue surrounding the incision. To this end, we successfully performed three-dimensional subsurface surgery with micron precision in human sclera <italic>in vitro</italic>. Photodisruption, the name for the laser-matter interaction that turns matter into plasma, can only be performed at a tight focus where the laser pulse intensities are high enough to cause optical breakdown. Under normal conditions, subsurface surgery is not possible in sclera because the sclera scatters visible light. Scattering was defeated using two methods. First, the sclera can be made transparent by injecting a dehydrating agent, such as Hypaque, a commonly used x-ray contrast agent. The transparency effects are reversible and cause no damage to living tissue. Second, a wavelength can be selected that is minimally scattered and absorbed, namely 1700 nm. Using low power linear measurements, we demonstrated that both of these methods allow for the beam to be tightly focused after traveling through the tissue. Using these techniques to increase focusing, a variety of incisions were made in sclera: the shape and location were controlled by scanning the laser focus spot in the tissue. Subsurface photodisruption has been achieved successfully <italic>in vitro </italic>human sclera with micron precision. Virtually any type of three-dimensional incision can be made in the bulk of the tissue. For the first time, we show a completely remote---cutting inside a tissue---method of performing a subsurface surgery in a highly scattering tissue. Similar techniques can be applied to other tissues, such as skin. This work paves the way for <italic> in vivo</italic> glaucoma studies.