OPTICAL MODELING OF RADIAL KERATOTOMY INCISION PATTERNS

PURPOSE: To determine the optical effects of higher-order corneal shap e variations resulting from radial keratotomy. METHODS: Videokeratosco pic height data were obtained postoperatively from several patients wh o had undergone radial keratotomy. For each of clear central zone size s 3.00 mm, 4.00 mm, and 4.75 mm, two patients were chosen randomly fro m the larger study group. Data obtained 2 weeks postoperatively from t hese six patients were decomposed into the Zernike polynomials, and th e low-order expansion terms were removed to disclose corneal height va riations (the radial keratotomy artifact). The artifact was applied to a schematic eye model, and exact ray-tracing was used to evaluate vis ual performance, which was defined as a function of pupil diameter, op tical zone (central clear zone) size, and radial keratotomy artifact c entration. RESULTS: The radial keratotomy artifact degrades visual per formance at midspatial frequencies more than it does at high spatial f requencies. This effect is most pronounced for smaller optical zones a nd for a pupil diameter of 4 mm. Visual performance remains nearly con stant for small decentration (0.5 mm or less) of the radial keratotomy optical zone from the corneal apex. CONCLUSIONS: Residual refractive error, corneal asphericity, and the radial keratotomy artifact all aff ect visual performance after radial keratotomy. Isolated effects of th e radial keratotomy artifact degrade visual performance, with the leve l of degradation dependent on pupil size, optical zone size, and centr ation of the procedure. More research is necessary to combine the radi al keratotomy artifact with changes in corneal asphericity and to furt her quantify the optical effects of radial keratotomy.