Experimental retinal ablation using a fourth-harmonic 266 nm laser coupled with an optical fiber probe.

Purpose: To explore the ablation potential of 266 nm laser pulses, with an intact porcine retina preparation.
Methods: Segments of porcine eyes were used in an in vitro preparation in which localized areas of intact retina and choroid could be exposed to 266 nm laser irradiation. The segments of ocular tissue were bathed in fluid, to mimic the intraocular environment. Contact between the probe and the retinal surface was established before the first laser pulse. Single or multiple pulses (5-7 ns duration) at fluence levels of 0.4 to 1.2 J/cm2 were delivered via a tapered fiber optic probe with a tip size of approximately 110 microm. The retinal tissue was then fixed and sectioned for histologic examination. The ablation depth and extent of damage were measured and related to fluence level and the number of pulses applied.
Results: Ablation of the inner retina was achieved by single pulses at fluence levels of 0.6 J/cm2 and higher. The depth of retinal ablation was highly dependent on fluence for lesions generated with a single pulse but less so for multiple pulses (3-10), particularly at lower fluence levels. Higher numbers of pulses (50-100) did not increase ablation depth in a predictable manner.
Conclusions: Pulsed laser (266 nm) irradiation at low pulse counts and high fluence levels is a possible alternative for localized retinal ablation with minimal collateral damage in a fluid environment.