Ablation of the cornea by using a low-energy excimer laser

We describe a new multipurpose method for corneal refractive surgery by using a focused excimer laser beam, which allows the application of a small, compact low-energy excimer laser. It is possible to ablate any area desired in the cornea without masking by scanning the focused beam. The ablation depths in freshly enucleated swine eyes were measured in relation to the number of laser pulses (at fixed fluence) and the pulse fluence at wavelengths lambda = 248 nm and lambda = 193 nm. The irradiation conditions were investigated to obtain smooth ablation of the corneal material over an area of about 1 cm2. The experiments show that smooth ablation is obtained when the ratio of the excimer laser beam spot diameter on the corneal surface and the displacement for one scanning step is given by a whole number. A simple model based on rectangular beam profiles is presented to exemplify this.