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CR Bruno, CJ Roberts, D Castellano, A Mahmoud, L Birnbaum, E Herderick; Topographic Analysis of Posterior Corneal Surface Changes After LASIK . Invest. Ophthalmol. Vis. Sci. 2002;43(13):164.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The purpose of this study is to investigate potential changes in the posterior surface after LASIK. Methods: Twenty-four eyes of 12 patients who elected to undergo LASIK surgery with a Summit Apex Plus laser, using a Kremeich-Barraquer microkeratome were examined at 1 day pre-op, 1 day, 1 week, 1 month and long term (10-12 months) post-op with an Orbscan II corneal topographer, with 2 exams in each session. A control group of 48 eyes of 24 subjects had 2 topographic maps taken at baseline, 1 day, 1 week and 1 month later, without undergoing a LASIK procedure. The topographic data were exported to custom software, The OSU Topography Tool, for analysis. The corneal topography was divided into 3 regions for analysis: central (2.75mm radius), middle (2.75-3.25mm radius) and outer (3.25-4.5mm radius). Post-op minus pre-op elevation differences were calculated with the surfaces aligned within the middle region, and the temporally corresponding repeated measures from baseline were subtracted for the normal subjects. The regional differences were statistically compared in both populations. Results: The one day post-op results were excluded due to processing errors and one patient was excluded due to inconsistent measurement between dual examinations within the same session. The posterior surface differences at 1 week were: centrally +28µm14µm (p<0.0001), peripherally -3µm9µm (p=0.08) in the surgical group and centrally +0.09µm10µm (p=0.96) peripherally -1µm11µm (p=0.49) in the normal group. At one month the results were: centrally +19µm8µm (p<0.0001), peripherally +1µm6µm (p=0.35) in the surgical group and centrally +0.09µm6µm (p=0.42), peripherally +0.13µm7µm (p=0.92) in the normal group. Long term the results were: centrally +16µm10µm (p=0.0002), peripherally +3µm8µm (p=0.24) in the surgical group. Long term follow up was not possible in the normal group. Conclusion: Our results show statistically significant changes in the posterior corneal shape, demonstrating increased central height. However, the dioptric change was clinically insignificant at < 0.25 D, and stable with time. Control subjects showed no significant differences on repeated measures using the same protocol.
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