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Determination of excimer laser ablation rate of the human cornea using in vivo Scheimpflug videography
H J Huebscher1, U Genth, T Seiler
1Augenklinik, Klinikum Berlin-Buch, Germany.
Purpose:
To determine in vivo the amount of human corneal tissue removed by each excimer laser pulse, the so-called ablation rate, during photorefractive keratectomy (PRK). There is confusion in the literature because the experimentally determined ablation rate of 0.4 to 0.5 microns per pulse differs from the nominal ablation rate of 0.23 to 0.3 microns per pulse, which is the value used in clinical procedures.
Methods:
Eleven eyes of 11 patients were treated with PRK for correction of myopia. The corneal curvature was determined by Scheimpflug videography before and immediately after surgery. Starting from this curvature change, the authors calculated the real ablation rate.
Results:
The real ablation rate is coincident with the nominal ablation rate and differs significantly from the ablation rate derived from deep keratectomy experiments.
Conclusions:
The outer layers of the cornea show significantly different ablation behavior than the deeper stroma. This information has clinical relevance for the predictability of intrastromal excimer laser procedures.