Influence Factors and Prediction of Noncontact Tonometry Measurements after Myopic and Astigmatism LASIK Surgery

Objective To evaluate the changes and influence factors of intraocular pressure (IOP) measurements by noncontact tonometry(NCT)after laser in situ keratomileusis(LASIK)for myopia and astig- matism,and to find a correction formula for predictive measured IOP. Methods Retrospective case series was performed on 93 patients (183 eyes)receiving primary LASIK for myopia and astigmatism in Peking Union Medical Collage Hospital from December 2005 to November 2006. IOP was measured by NCT before and after operation including 2 week, 1 month, and 3 months after LASIK. The amount of IOP change was computed and its relation to different variables was analyzed. Correction formula for predictive IOP and IOP change were e- valuated by multiple linear regression analysis. Results IOP of NCT was reduced by a mean of (5.74±2.03 ) mmHg at 3 months after LASIK. The change in IOP was not related to gender or age of the patient,but related to preoperative diopter significantly. Multiple linear regression analysis of the IOP before and after LASIK showed a significant correlation between the measured IOP and preoperative lOP and ablation depth(R2=0.442, P <0.001). Predictive measured IOP after LASIK=5.175+0.411× preoperative IOP -0.0205× ablation depth, Change of measured IOP after LASIK=0.589× preoperative IOP+0.0205× ablation depth -5.175. Conclusions Through comparing actual and predictive measured IOP and detecting hypertension in time, we can avoid un- derestimation of IOP after LASIK and detect potential glaucoma patients. Although correction formula can be used to estimate predictive measured IOP after LASIK, alternative methods should be investigated to assess IOP independent of corneal change after LASIK. Key words: Laser in situ keratomileusis(LASIK); Noucontact tonometry(NCT); Intraocular pressure(IOP);  Prediction