[Consequences of different ablation rates in Bowman's membrane and corneal stroma for photorefractive keratectomy].

If photorefractive keratectomy (PRK) is performed with an ArF-excimer-laser, the existence of different ablation rates in Bowman's membrane and corneal stroma is of crucial importance, as ablation rates are considered to be constant in PRK. Consequently, if photoablation cannot be confined to Bowman's layer alone, at least two new surfaces with different refractive powers would result. For the correction of myopia with PRK, different ablation rates would mean that: (1) the central corneal surface with the desired refractive power is smaller than the total ablation zone. The lower the ablation rate in Bowman's layer compared to that of stroma, the smaller the area of desired refraction. (2) the maximum attainable refractive change will also be smaller, the lower ablation rate in Bowman's layer is compared to that of stroma. (3) Enlargement of the central zone of desired refraction is limited by the maximum acceptable ablation depth.