Figure 7.

(a) A graphical illustration of the relationship between the depth of ablation required for a given ablation diameter to generate a given dioptric correction. This relationship known as the Munnerlyn formula demonstrated that for very small beam diameters corrections up to −2.5 D could be achieved without completely ablating through Bowman's membrane (shown in yellow). Attempts to preserve Bowman's membrane in the earliest studies resulted in the use of small beam diameters, but these were rapidly abandoned after extensive laboratory studies showed that the preservation of the membrane was not essential. The postoperative uniformity of the corneal epithelium is demonstrated in a human cornea several weeks after surgery in (c), which compares favourably with an unablated area of the same cornea shown in (b).