We report the evaluation of a system which delivers the 5th harmonic of an Nd:YAG (213nm) via optical fibre to ocular
tissue sites. The 213nm beam is concentrated, using a hollow glass taper, prior to launch into 200 μm or 600 μm core
diameter silica/silica optical fibre. The fibre tip was tapered to enhance the fluence delivered. An operating window of
fluence values that could be delivered via 330 - 1100mm lengths of optical fibre was determined. The lower value of
0.2J/cm2 determined by the ablation threshold of the tissue and the upper value of 1.3J/cm2 by the launch, transmission
and tip characteristics of the optical fibre. The fluence output decreased as a function of both transmitted pulse energy
and number of pulses transmitted. Fresh retinal tissue was cleanly ablated with minimal damage to the surrounding
tissue. Lesions were generated using 1, 3 and 10 pulses with fluences from 0.2 to 1.0J/cm2. The lesion depth
demonstrated clear dose dependence. Lesions generated in ex vivo preparations of human trabecular meshwork in a fluid
environment also demonstrated dose dependence, 50 pulses being sufficient to create a hole within the trabecular
meshwork extending to Schlemm's canal. The dose dependence of the ablation depth combined with the ability of this
technique to create a conduit through to Schlemm's canal demonstrates the potential of this technique for
ophthalmological applications requiring precise and controlled intraocular tissue removal and has potential applications
in the treatment and management of glaucoma.
We report the use of an ultraviolet (UV) laser and optical fibre arrangement capable of precise and controllable tissue
ablation. The 5th (213nm) and 4th (266nm) harmonics of a Nd:YAG laser were launched into optical fibres using a
hollow glass taper to concentrate the beam. Standard and modified silica/silica optical fibres were used, all
commercially available. The available energy and fluence, as a function of optical fibre length, were evaluated and
maximised. Single 5ns pulses were used to ablate both fresh porcine retina and in vivo rat trabecular meshwork.
Fluences of 0.4 to 4.0 J/cm2 of 266nm and 0.2 to 1.0 J/cm2 of 213nm were used respectively. Thus demonstrating the
potential use of this system for intraocular surgical applications.