Investigation of corneal ablation efficiency using ultraviolet 213-nm solid state laser pulses.
OBJECTIVE
To determine the threshold and efficiency of corneal ablation for various values of laser fluence at the ultraviolet wave length of 213 nm.


METHODS
A commercial Q-switched Nd:YAG laser was used to produce the fifth harmonic wavelength of 213 nm. Ablation trials were carried out on porcine corneas. Slit ablations of dimensions 0.5 x 2.5 mm were performed using seven values of laser fluence to obtain the most efficient fluence for ablation. The morphology of each ablation was obtained using a computer-automated confocal profiling system. These profiles were then analyzed to determine the ablation depth for the range of fluence values used.


RESULTS
A fluence in the region of 200 mJ/cm2 was found to be the most efficient for ablation. The efficiency in this region was approximately 0.35 mm3/J, and the ablation rate was found to be 0.6 microm/pulse. The ablation threshold was found to occur at a fluence of 50 mJ/cm2. In the region of highest efficiency, the peak varied slightly in the fluence range between 150 and 250 mJ/cm2.


CONCLUSIONS
This study confirms that the corneal ablation properties at 213 nm are comparable with those at the 193-nm excimer laser wavelength. Increased pulse energy was obtained for the fifth harmonic of Nd:YAG lasers at 213 nm through the use of new nonlinear optical crystals to perform the frequency conversion. A solid state laser is feasible to replace the excimer gas laser for performing refractive surgery procedures. For the first time, the increased energy at 213 nm allows large-beam ablations to be performed at this wavelength.
Dair
G T
GT
Lions Eye Institute, Center for Ophthalmology and Visual Science, University of Western Australia, Nedlands. gdair@cyllene.uwa.edu.au
Pelouch
W S
WS
van Saarloos
P P
PP
Lloyd
D J
DJ
Linares
S M
SM
Reinholz
F
F
D000818:Animals; D003315:Cornea / Q000601:surgery*; D054018:Lasers, Excimer; D018903:Photorefractive Keratectomy / Q000295:instrumentation / Q000379:methods*; D013552:Swine; D014466:Ultraviolet Rays