Analysis on corneal biomechanical changes before and after sub-Bowmann's keratomileusis for high myopia

Abstract

Objective To analyze and investigate the influence of sub-Bowmann's keratomileusis (SBK) on corneal biomechanical properties in high myopia evaluated by the Goldmann correlated intraocular pressure (IOPg), corneal compensated IOP (IOPcc), corneal resistance factor (CRF), corneal hysteresis (CH), TimeIn, TimeOut and their changing values. Methods In this prospective case series study, there were 36 subjects (65 eyes) with high myopia underwent SBK. Their mean age was (22.9±3.6) years (ranged:19 to 34 years) and spherical equivalent was (-8.35±1.21)diopters (D) (range:-6.375 to -12.50 D). The IOPg, IOPcc, CR, CH, TimeIn and TimeOut were obtained with Ocular Response Analyzer (ORA) preoperatively and 1 month postoperatively. The values were analyzed before and after surgery using a paired t test. A multiple regression analysis and Pearson correlation were used to investigate the factors affecting the changing values. Results The mean preoperative values of IOPg, IOPcc, CRF, CH , TimeIn, TimeOut and the difference between TimeOut and TimeIn were (17.5±3.0)mmHg, (17.6±2.9)mmHg, (11.1±1.4)mmHg, (10.5±1.3)mmHg, (8.0±0.4)ms, (18.6±0.2)ms and (10.7±0.4)ms, respectively, and the mean values 1 month postoperative were (12.4±3.5)mmHg,(16.4±3.3)mmHg, (7.0±1.2)mmHg, (7.5±1.0)mmHg, (7.2±0.5)ms, (18.4±0.2)ms and(11.2±0.5)ms,respectively. The differences between preoperative and postoperative status were statistically significant (t=14.2, 3.5, 28.1, 24.9, 17.4, 16.2, -10.7, P＜0.01 for all). There was a trend toward positive correlation between ablation depth (AD) and △ IOPg (r=0.247, P=0.047), as well as between AD and △CRF (r=0.298, P=0.016); but no significant correlations were found between AD and other indices such as △IOPcc, △CH, △TimeIn, △TimeOut and the changing in the difference between TimeOut and TimeIn. Conclusion SBK for high myopia substantially weaken corneal properties and induce some changes in corneal biomechanical singnals, which are related to ablation depth to some extent. Key words: Myopia; Keratomileusis,laser in situ; Corneal biomechanics