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J Cataract Refract Surg. 2004 Feb;30(2):464-70.

Effect of excimer laser beam delivery and beam shaping on corneal sphericity in photorefractive keratectomy.

Author information

1
Department of Ophthalmology, Charité-Campus Virchow Hospital, Humboldt University of Berlin, Berlin, Germany. bertmueller@hotmail.com

Abstract

PURPOSE:

To evaluate the impact of beam delivery and beam shaping on corneal profiles after myopic excimer laser photorefractive keratectomy (PRK).

SETTING:

Department of Ophthalmology, Charité-Campus Virchow Hospital, Humboldt University of Berlin, Berlin, Germany.

METHODS:

Standard myopic 193 nm excimer laser PRK of -3.0 diopters (D) and -6.0 D was performed in porcine eyes using 2 commercially available broad-beam lasers with band-mask and fractal-mask beam shaping, 2 flying-spot lasers, and a scanning-slit laser. A silicone replica was obtained to preserve the corneal profile and was measured with a dynamic focusing topometry system.

RESULTS:

The scanning-slit and flying-spot lasers created uniform profiles comparable to those in an untreated control group. Both broad-beam lasers with band-mask and fractal-mask beam shaping created central islands and paracentral profile valleys of 15.10 microm and 17.00 microm maximum height after -3.0 D PRK and 26.45 microm and 24.31 microm after -6.0 D PRK. An anti-central-island program, which applied a series of laser pulses centrally to compensate for the central profile elevations, did not eliminate the islands. Stromal surface roughness increased with ablation depth and was significantly worse after scanning-slit ablation than after broad-beam ablation.

CONCLUSIONS:

Laser-induced deviations from the intended uniform corneal profiles were associated with broad-beam ablation and increased ablation depth and therefore lessened the predictability of the refractive outcomes. Scanning-slit and flying-spot systems produced predictably uniform corneal profiles.

PMID:
15030843
DOI:
10.1016/S0886-3350(03)00559-5
[Indexed for MEDLINE]

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