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E Cantera, R Mattioli, A Pinciaroli, I Cantera, C Cantera; Corneal, Ocular and Internal Aberrations Before and After LASIK Surgery . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2042.
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© ARVO (1962-2015); The Authors (2016-present)
Purposes: 1) To evaluate the correlation between eye wavefront or «ocular-OPD», from a S-H wavefront analyser, and «corneal-OPD», from a reflective arc-step corneal topographer, on a set of low-aberration normal pre and post-LASIK. 2) To evaluate the aberration increase or decrease pre-post LASIK with both methods 3) To map the internal OPD and to verify if it remains stable before and after surgery. Methods: 43 ocular-OPD maps have been displayed beside 43 corresponding corneal-OPD maps by software SCOUT.EXE, beta-Rel. 3.2.0 (Optikon, Roma, Italy). The ocular-OPD were imported from Zywave (B&L-Technolas, Munich, Germany), by 2nd to 5th order Zernikje plus pupil data. The corneal topographies were imported by a Keratron (Optikon, Roma, Italy). Tests were distributed as follows: 9 eyes both pre- and post- LASIK, 12 post LASIK, 12 normal pre-operatory and 1 sub-clinical keratoconus. All maps have been re-sampled so to have the same pupil size of 5mm. Surgeries correction ranged from -1 to -7D sphere and 0 to 3.75D astigmatism. Beside the aberrations RMS measures, a subjective «match score» from 0 to 4 has been adopted to compare Ocular with Corneal OPD maps as well as to compare pre with post «Internal-OPD» maps has been devised to classify the visual pattern correlation. Results: High order aberrations (3rd to 5th order): Pre-operative ocular-OPD average 0.22 um (corresponding to 0.24 D defocus equiv.), std. = 0.08, and corneal-OPD average 0.24 um, std.= 0.08. Post-operative ocular-OPD average 0.31 um, std.= 0.12, corneal-OPD avg.= 0.33 um, std.=0.14. About 70% corneal OPD maps matched (score 2 to 4) with ocular OPD. In 50% cases pre-post LASIK the internal-OPDs before and after surgery matched (score 3 or 4) pretty well. Internal (i.e.: ocular-minus-corneal) astigmatism was avg.= 0.95D, std.= 0,42, generally against the rule (axis avg.= 94°), with very small differences post-pre (avg.= 0.12D, std.= 0.14). Conclusions: 1) Even in low-aberration pre and post LASIK, the corneal OPD shows to be a good predictor of visual performance. 2) Standard LASIK procedure, as an average but not in all cases, slightly increased both corneal and ocular OPD RMS aberrations, measured at pupil = 5mm. 3) To get reliable «Internal-OPD» maps was not easy, because changes in pupil sizes and in maps centering tended to create fuzzy results in the subtraction. Nevertheless, in 50% of "pre+post" cases, the Internal-OPD was succesfully mapped and found stable between pre and post LASIK surgery.
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