Optical modeling of radial keratotomy incision patterns

PURPOSE: To determine the optical effects of higher-order corneal shape variations resulting from radial keratotomy. METHODS: Videokeratoscopic height data were obtained postoperatively from several patients who had undergone radial keratotomy. For each of clear central zone sizes 3.00 mm, 4.00 mm, and 4.75 mm, two patients were chosen randomly from the larger study group. Data obtained 2 weeks postoperatively from these six patients were decomposed into the Zernike polynomials, and the low-order expansion terms were removed to disclose corneal height variations (the radial keratotomy artifact). The artifact was applied to a schematic eye model, and exact ray- tracing was used to evaluate visual performance, which was defined as a function of pupil diameter, optical zone (central clear zone) size, and radial keratotomy artifact centration. RESULTS: The radial keratotomy artifact degrades visual performance at midspatial frequencies more than it does at high spatial frequencies. This effect is most pronounced for smaller optical zones and for a pupil diameter of 4 min. Visual performance remains nearly constant 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 affect visual performance after radial keratotomy. Isolated effects of the radial keratotomy artifact degrade visual performance, with the level of degradation dependent on pupil size, optical zone size, and centration of the procedure. More research is necessary to combine the radial keratotomy artifact with changes in corneal asphericity and to further quantify the optical effects of radial keratotomy.