This proposal intends to generate prescribed negative cylinder excimer laser ablations using technology analogous to that presently being used for the correction of myopia in human clinical trials. The proposed devise would correct high amounts of astigmatism for which treatment with glasses and contact lenses is problematic because of induced binocular vision problems due to poor lens orientation. A prototype device for generating prescribed cylindrical ablations will be developed and evaluated on PMMA test surfaces to test for the accuracy and reliability of system function. Alignment techniques, which provide for axis orientation and ablation centering, will also be evaluated. A prototype instrument is presently being developed and should be operational by the time of funding. The device will provide for meridional adjustment of 1/3 degree intervals, slit width adjustment within 9 u per step and precise rate of closure. The design in intended to exceed the expected and patient ablation tolerances of + 0.25 D and + 2.0 degrees. PMMA testing will be carried out on two types of surfaces, flat samples and spherical contact lenses. For the samples having cylindrical component, the power of the prescribed ablation cylinder will be equal to the complement of the sample cylinder. Thus, reduction of the cylindrical component to zero would provide verification of the ablation model, and residual cylinder would indicate an error in the ablation algorithm, hardware, or alignment procedures. For clinical application eye alignment procedures will be developed during that latter phases of the project. This work will be carried out in parallel with the other studies.
