Topography-Guided Refractive Astigmatism Outcomes: Predictions Comparing Three Different Programming Methods.

PURPOSE: To identify the laser programming strategy that will achieve optimal refractive outcomes of LASIK with a topography-guided laser for eyes with a disparity between cylinder measured by manifest refraction and cylinder measured by topography. SETTING: Six surgeons at 5 clinical sites in the USA. DESIGN: Retrospective data review. METHODS: Preoperative, treatment, and postoperative data on 52 eyes that underwent topography-guided LASIK with the WaveLight EX500 Contoura® Vision excimer laser ablation profile in which the vectors representing the preoperative refractive cylinder and the cylinder measured by the WaveLight® Topolyzer™ VARIO Diagnostic Device (Vario cylinder) differed by >/= 0.50D and/or >/= 10 degrees of orientation were analyzed retrospectively. Data were contributed by six surgeons using the laser at 5 different clinical sites. Vector analysis of postoperative cylindrical refractive error and the actual laser programming strategy was used to calculate the cylindrical correction that would, theoretically, have completely eliminated postoperative refractive cylinder. This was compared to expected results using the preoperative manifest cylinder, the topographic cylinder, and the Phorcides Analytic Engine (Phorcides LLC, North Oaks MN; Phorcides). For analysis, subjects were stratified on the basis of the vector difference between Manifest and Topo cylinder (High, >0.75 D; and Low, ≤0.75 D). RESULTS: The poorest calculated theoretical outcomes were obtained with the manifest refraction (centroid: -0.43, 0.22; mean calculated error vector: 0.56 ± 0.42 D; p=ns). Better outcomes were obtained with the topographically measured refraction (centroid: 0.37, 0.02; mean calculated error vector: 0.47 ± 0.33 D; p=ns). The best outcomes were obtained with Phorcides (centroid: -0.15, 0.06; mean calculated error vector: 0.39 ± 0.28 D; p=ns). The mean error vector magnitude in the Phorcides Low group was significantly lower than for the Manifest and Topo Low groups (0.26 D vs 0.48 D and 0.33 D; p<0.01). The mean error magnitude in the Phorcides High group was nearly 0.25 D lower than for the Manifest High group (0.48 D vs 0.70 D; p<0.01), but was the same as for the Topo High group (0.48 D vs 0.48 D). CONCLUSION: Our study suggests that using the topographically measured cylinder or the cylinder selected by Phorcides will produce more desirable refractive outcomes than entry of the preoperative refractive cylinder as the basis for correction of myopia and myopic astigmatism with the WaveLight Contoura Vision excimer laser.

Absence of keratectasia after LASIK in eyes with preoperative central corneal thickness of 450 to 500 microns.

PURPOSE: To determine whether preoperative central corneal thickness less than or equal to 500 microm is an independent risk factor for development of keratectasia following LASIK. METHODS: Chart review was performed for 109 eyes with preoperative central corneal thickness of 452 to 500 microm in 69 patients who underwent LASIK between September 2000 and July 2005 and had no known risk factors for keratectasia. All eyes included in this analysis had postoperative manifest refractions at follow-up at 1-month and 12-months or greater (median: 452 days; range: 365 to 1980 days). RESULTS: Attempted correction (spherical equivalent refraction) ranged from +3.13 to -7.75 diopters. There were no clinical signs of keratectasia at any postoperative visits in the 109 eyes in this study. There was no statistically significant change in mean spherical equivalent or manifest cylinder from the 1-month follow-up examination to the last documented visit (12 months or greater). No correlation was found for preoperative pachymetry and refractive change between postoperative examinations at 1 month and 12 months or greater. Double-angle vector analysis determined the directional shift in postoperative refractive cylinder was not statistically significant from zero (P > .05). CONCLUSIONS: In this group of 109 LASIK-treated eyes with preoperative central corneal thickness less than or equal to 500 microm that were screened for known keratectasia risk factors, there was no evidence of postoperative keratectasia.

Fulfilling the promise of laser refractive surgery.

PURPOSE: To review the characteristics required to perform accurate and precise laser refractive surgery relative to the current state of the art and the technology improvements needed in the future. METHODS: The general characteristics for laser refractive surgery are identified and their relative contributions to a successful result considered. For each characteristic, the degree to which improvements in technology are likely to improve results is discussed. RESULTS: The environment (surgeon, site), technology (laser, aberrometer), and patient are identified as key factors affecting results. Although aberrometers appear to be clinically sufficient, improvements in laser beam characteristics and delivery should improve system consistency. Current registration technology may be a factor in variability from patient to patient, but the greatest contribution in this regard would appear to be patient biomechanical and healing response factors. CONCLUSIONS: Wavefront-guided laser refractive surgery has demonstrated an ability to be better than conventional surgery. Improvements in laser technology, registration technology, and biomechanical diagnostics are expected to further improve results. These potential improvements are expected to reduce variability and suggest that the final potential of this technology has not yet been realized.