Mass spectroscopic analysis of excimer laser ablated material from human corneal tissue

Abstract

The clinical feasibility of photorefractive keratectomy depends on the surface structure of the ablated cornea. Two factors that influence the remodeled surface are the homogeneity of the energy distribution and the properties of the laser source (energy and wavelength). Currently, the homogeneity of the beam is difficult to control. The second factor, laser source properties, was the focus of this study. We investigated the effect of laser wavelength and energy by analyzing the reaction products of photoablation. We monitored the fragments produced by UV-laser ablation of human corneas using mass spectroscopy in the range of 0 to 100 atomic mass units. At 248 nm (KrF), average photon energy was 5 mJ/cm2, increased to 90 mJ/cm2 by intervals of 5 mJ/cm2. At 193 nm (ArF), photon energy was increased by the same interval from 5 mJ/cm2 to 80 mJ/cm2. Our experiments showed that there was a fluence threshold of approximately 40 mJ/cm2 at 193 nm (ArF) and 50 mJ/cm2 at 248 nm (KrF). Exceeding this threshold led to sudden increases in the number and relative intensity of fragment peaks in mass spectroscopy. This indicates the onset of multiple-photon processes and effective photochemical breakdown. There was a significant difference between both wavelengths in the distribution of mass peaks, indicating higher ionization power at 193 nm.

Dynamics of ablation plume particles generated during excimer laser corneal ablation

“…Although reported data [8] support present modeling of the cornea ablation plume particles as water spherules, Raman scattering measurements were performed to confirm the composition of the plume particles in situ. Raman spectra were recorded corresponding to the peak of the plume scattering signal as analyzed above.…”

“…To gain insight into the fundamental proderstood. For ablation in the vicinity of the ArF laser's 193 nm radiation, it has been proposed that the predominant process for organic materials is ablative PhotodecomPosition (APD) [5,61, which is also considered fundamental in the ab-Accepted for publication October 11, 1994. cesses of UV laser ablation, several investigations have focused on the resulting ablation plume, including high-speed photographic techniques [lo] and mass spectrometric analysis [8,111. The present report covers a quantitative technique for the analysis of ablation plumes using in situ timeresolved laser light scattering.…”

Endothelial cell density after photorefractive keratectomy for moderate myopia using a 213 nm solid-state laser system

“…1 The extent of primary actinic damage depends primarily on the absorption coefficient of the cornea, 29 and secondary actinic damage depends on the spectrum and the intensity of the fluorescence. The cornea exhibits a very high absorption coefficient at both laser wavelengths 25,30,31 ; therefore, primary actinic damage is expected to be restricted to small depths in both cases. However, the potential implication of corneal stroma and endothelium to secondary (fluorescence) radiation cannot be estimated as little is known about the spectral characteristics of the fluorescence during 213 nm ablation of the cornea.…”

Short communications

“…In three cases, previous ultrasound examinations performed as late as 22 weeks gestation were reported as normal. In utero hydrocephalus, associated with Galenic AVM, has been described in three cases, and is reportedly due to mechanical obstruction of the aqueduct of Sylvius [7]. Fetal cardiomegaly was reported in nearly all cases, and the impression of hepatomegaly recorded in four patients.…”

“…With the increasing use of duplex scanning systems in obstetric ultrasound, vascular abnormalities in the fetus will be diagnosed more frequently. There have been three cases reported of the use of combined doppler and real-time sonography in the prenatal diagnosis of AVM of the vein of Galen [1,2,7]. We report an additional case of this entity, with the diagnosis confirmed by doppler sonography, and review the literature.…”