Posterior Corneal Surface Changes After Myopic Laser In Situ Keratomileusis

BackgroundLaser in situ keratomileusis(LASIK), which correct ametropia by changing thecurvature of the anterior cornea, is popular used today, because of its safety, stabilization, predictability. Numerous studies were concentrated on the change of the anterior corneal surface. However, according to the biodynamic principle of a closure glomus梕yeball, the posterior corneal surface tends to change its curvature with the decrease of the corneal thickness responding to the action of intraocular pressure. Moreover, the changes of the posterior corneal surface probably affect the effect of LASIK directly or indirectly, and probably become the risk of some complication directly or potentially. With the clinic use of Orbscan II ,the change of the posterior corneal surface can be detected after LASIK, it make us evaluate operating effects roundly.1. ObjectiveTo assess the changes of che posterior corneal power, irregular and difference, and the correlative factors of these changes after LASIK. And discuss the probable clinical mechanism of these changes.2. methods2.1 ParticipantsA total 51 eyes of 26 patients(15male, 11 female) were studied with myopia ranging from -2.25D to -12.5D (mean -6.877D?.564D) who underwent LASIK in our eye center.2.2 Study methodNaked vision, best corrected visual acuity, anterior segment of eye, fundus of eye, refraction and intraocular pressure and Orbscan II were determined routinely preoperatively and at one week, one month and three month postoperatively. Ultrasound pachymetry was also measured preoperative.2.3 Observational componentThe changes of naked vision, best corrected vision acuity, intraocular pressure, corneal thickness and power, irregular and difference of the posterior comeal surface, and the simulated keratoscope reading of the anterior cornea were evaluated.2.4 Statistical AnalysisData were processed with SPSS 10.0 software, each group data were analyzed by Independent-Samples t Test and multiple regression analysis. 3. Results3.1 The changes of the posterior corneal surface after LASIK3.1.1 The change of figures of Orbscan II after LASIKThe colour of the posterior corneal surface corresponding to the ablation changed to be red.3.1.2 The changes of posterior corneal power after LASIKThe postoperative posterior corneal power was increased (p < 0.001) , it was no statistical difference between each postoperative period (p>0.05) . (Independent-Samples T Test)3.1.3 The changes of posterior corneal irregular after LASIK5In 3.0mm central corneal zoon, the postoperative posterior corneal irregular was significantly different to the preoperative (p<0.01) , but there was no statistical difference between each postoperative period (p>0.05) . In 5.0mm range, the posterior corneal irregular also was significant different between preoperatively and postoperatively( p < 0.01), there is statistical different between the post-op-1 w period and post-op-1m period, as well as the post-op-Iw period and post-op-3m period (p < 0.05) , but there was no significant difference between post-op-lm period and post-op-3m period. (Independent-Samples T Test)3.1.4 The changes of posterior corneal difference after LASIK The posterior corneal difference between each postoperative period was significantly greater than the preoperative (p < 0.01) , but there was no significant difference between the post-op-lw period and post-op-lm period, as well as the post-op-Iw period and post-op-3m period (p > 0.05) . (Independent-Samples T Test)3.2 Analyse the related factor of the change of the posterior cornea3.2.1 The change of the posterior corneal power after operation was correlated to intraocular pressure, preoperative corneal thickness and the myopia diopter that was practically corrected in operation.3.2.2 The change of the posterior corneal difference after operation was related to preoperative intraocular pressure and corneal thickness and the my...