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In spite of the fact that more than one hundred fifty clinical excimer laser units designed for corneal surgery have been developed and sold commercially, substantial technical issues remain uncertain and have not been carefully studied. There are quantitative and qualitative uncertainties which exist about many aspects of the laser-tissue interactions. It has proven to be extremely difficult to obtain accurate data describing the amount of tissue removed per pulse in living corneal tissues. The result of this uncertainty is the use of a large range of ablation figures, and in some cases, the use of corrective factors which try to compensate for many of the unknown factors empirically. Ablation algorithms remove tissue by scanning a slit over the corneal surface, or by using a series of circular exposures of increasing or decreasing diameter. No data is available to suggest which patterns optimize accuracy, precision and clarity of healing. Relating to surgery, clinical uncertainties persist. The optimal physical factors for laser ablation including the size and pattern of the ablated cornea are not known. Operative techniques and postoperative care differ widely among investigators. Individual biological variation in corneal healing is suspected but not confirmed.