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R Mattioli, E Cantera, M Camellin, S Frondizi, A Rubeo, NK Tripoli; A Software and Model to Represent Corneal Wavefront from Corneal Topography and its Evaluation on LASIK an LASEK Refractive Surgeries . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2039.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To represent the components of eye aberrations, i.e. the overall «Ocular OPD» from wavefront analysis, including the «Corneal OPD» from reflective arc-step corneal topography and the «Internal OPD,» as the difference between the two, and to show all three in the same format, a clinically useful representation for evaluating vision. Methods: Within the Keratron Scout corneal topographer software, Rel.3.2.0 (Optikon 2000, Rome, Italy) a window and an optical model has been developed to calculate and represent the component of the eye aberrations owed to the cornea-air interface. This «Corneal OPD» is decomposed into Zernike polynomial up to the 7th order. Users can select individual Zernike components and the pupil size and can move off-pupil-centre on the resulting OPD map. The eye visual performances of the OPD are shown as: Ray-tracing, PSF, simulated Visual Acuity tests, MTF and plots of Visual Quality versus pupil size. Zernike signed or RMS values are plotted according the dual-indices pyramid scheme recommended by OSA, by histograms and a 3D «RMS skyline.» Wavefront map data, as Zernike coefficients plus pupil size, can be also be input from any wavefront analyser and represented as «Ocular OPD» maps. The «Internal OPD,» as the difference between «Corneal OPD» and «Ocular OPD,» is also mapped. For evaluation, a set of 70 «Ocular OPD» were acquired and imported from two different S-H wavefront analysers, and the corresponding 70 «Corneal OPD» were imported from Keratron topographers.. Tests were from: 9 eyes both pre- and post- LASIK, 10 eyes both pre- and post- LESIK, 12 post LASIK, 17 normal or preoperative, 1 sub-clinical keratoconus and 2 PTK patients. All maps were taken or re-sampled to the pupil size of 5mm. A subjective «match score» from 0 to 4 has been adopted to compare maps. Results: About 70% of high order corneal OPD maps matched (score 2 to 4) with equivalent ocular OPD. In 50% cases pre-post LASIK and pre-post LASEK the internal-OPDs before and after surgery matched (score 3 or 4) reasonably well. The "Internal Astigmatism" avg = 0.90 D, sd = 0.37, was generally against the rule (axis avg = 92°), and showed very small differences post-pre (avg = 0.05 D, sd = 0.22). Conclusion: The «Corneal OPD,» «Ocular OPD» and «Internal OPD» implemented on the Keratron Scout software are new, valuable tools for evaluating the sources of eye aberrations beyond the measures of corneal topography and wavefront analysis alone.
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