[Laser-induced pressure waves in the eye. Propagation characteristics].
BACKGROUND
The characteristics of shock waves during photoablation were investigated for an IR and a UV laser. These stress waves may be harmful to ocular structures.


METHODS
The amplitude of shock waves was measured by a needle-shaped hydrophone in enucleated porcine eyes during excimer laser (193 nm, 23 ns, diameter of ablation 1.5-7.5 mm) and Er:YAG laser photoablation (2.94 microns, 200 microseconds, 1.2 mJ/cm2, diameter of ablation 4 mm).


RESULTS
With the excimer laser at ablation zones larger than 4.5 mm, a pressure focus occurs at a distance of 4-6 mm behind the cornea. The pressure amplitudes are smaller than 80 bar for a fluence of 180 mJ/cm2 and decrease steadily to values below 10 bar towards the retinal level. Higher fluences produce higher pressure values; in the range of 60 to 220 mJ/cm2 the relation is linear. For the Er:YAG laser, pressure amplitudes are smaller than 0.5 bar.


CONCLUSIONS
Mechanical damage of the retina is unlikely during excimer-or Er:YAG-laser ablation. The existence of a pressure focus may result in mechanical damages of the posterior lens or anterior vitreous at large ablation diameters. During Er:YAG laser ablation, shock waves could not be detected with our measurements. Theoretical estimations yield values of less than 700 mbar at a fluence of 1.2 J/cm2. The pressure load of the endothelium is independent of diameter but dependent on fluence.
Spörl
E
E
Augenklinik, Universitätsklinikum Carl-Gustav Carus, Technische Universität Dresden.
Gruchmann
T
T
Genth
U
U
Mierdel
P
P
Seiler
T
T
D000818:Animals; D003315:Cornea / Q000503:physiopathology / Q000601:surgery*; D004867:Equipment Design; D006874:Hydrostatic Pressure; D054018:Lasers, Excimer; D018903:Photorefractive Keratectomy / Q000295:instrumentation*; D012307:Risk Factors; D013552:Swine