Using 193 nrn Excimer Laser light to reshape the cornea has been shown to be an effective way to correct myopia in man"2 One way to achieve the controlled shape is to create a large diameter Excimer beam, and pass it through a computer controlled ins diaphragm. As the diaphragm closes, progressively less laser pulses reach the outer portions of the treatment area, while all the pulses reach the center region, effectively flattening the cornea. The resultant correction is spherical, and does not correct astigmatism. This paper discusses the use of a motor controlled slit to correct astigmatism in a similar manner to myopia. The mechanism described combines an iris diaphragm and adjustable slit for correcting myopia, astigmatism, or a combination of the two. The slit mechanism also rotates so the slit axis can be aligned with the patient's astigmatic axis. All motions are motor driven under computer control, with encoder feedback to ensure correct positioning. Initial test medium was PMMA, which has ablation characteristics similar to human stromal tissue. Mechanical profile scans and lensometer tests of the PMMA test blocks were performed to verify the correct ablation pattern. Animal eyes were ablated and tested for astigmatic induction.