Gradient index (GRIN) lens multimode fiber probe for laser induced breakdown in the eye

A model laser surgical probe was designed and built to employ laser induced breakdown (LIB) in cutting fibrovascular membranes within the vitreous cavity of the eye. Current surgical techniques for removing such membranes from eyes with severe proliferative diabetic retinopathy or similar proliferative retinopathies involve cutting the membranes with microscissors or other micro-cutting devices. The mechanical movement of scissor blades may damage adjacent tissues directly or by shearing and traction. A laser cutting system that uses optical breakdown would reduce such mechanical damage but may introduce collateral laser damage. The probe is a simple design of a gradient index (GRIN) lens attached to the tip of a multimode fiber. It is designed to fit through a sclerotomy incision and enter the vitreous cavity for work anterior to the retina. The laser light is focused close to the tip of the probe without causing GRIN lens damage. Thus a widely divergent beam behind the focus will diminish potential laser damage posterior to the target tissue. A Nd: YAG 1064 nm 10 ns pulsed laser was used with the probe inserted into a cell of tap water. Threshold data for laser induced breakdown was taken and fit to a probit curve. The data was compared with past LIB threshold data. The radiant exposure versus distance from the probe was plotted via spot size measurements. This measurement gave a rough indication of the distance the probe must remain from the retina to be well below retinal maximum permissible exposure (MPE) levels. In vitro threshold measurements of bovine vitreous1 were taken and compared to the water threshold. Finally, collagen membranes were lased with the probe to demonstrate its functional application.

Duke Scholars

Author Cynthia Ann Toth Ophthalmology, Vitreoretinal Diseases & Surgery