Free-Electron Laser (FEL) Ablation of Ocular Tissues

The purpose of the present study was to investigate the ablation characteristics of free-electron laser (FEL) pulses at 5.3 μm and 6.0 μm on ocular tissues. The advanced FEL was developed by the Los Alamos National Laboratory. It operates in the 4–7 μm range, with a macropulse duration of 10 μs and repetition rate of 10 Hz. Each macropulse consists of a train of micropulses that are 15 ps in pulse duration separated by 10 ns. The output energy of macropulses can be adjusted from 5 to 120 mJ. Five transplant grade corneal-scleral buttons preserved in corneal storage medium were used. Wavelengths 5.3 and 6.0 μm were selected based on Fourier-transform infrared absorption spectra of a type I collagen film.

Ocular tissue cuts made at 6.0 μm revealed a well-defined ablation boundary with a lateral tissue damage at 10±2 μm. The ablation boundary of the corneal cuts made at 5.3 μm revealed tissue disruption with thermally denatured tissue constituents with loss of organised structure. The lateral dimension of this effect extended up to 220 μm.

It was concluded first that Fourier-transform infrared absorption spectra may be useful in selecting laser ablation wavelengths, and second that lasers emitting near 6 μm achieve excellent spatial confinement of laser energy secondary to both protein and water energy partitioning. This wavelength may have potential for cutting ocular tissue such as cornea, sclera, vitreous or lens, because of energy partitioning.