Abstract

Objective The aim of this study was to investigate the corneal resistance factor (CRF) and corneal hysteresis (CH) before laser in situ keratomileusis (LASIK) and to determine their relationship to central corneal thickness (CCT) and to compare the biomechanical properties of the preoperative and postoperative periods of LASIK surgery.Methods This was a case-control study.Eighty-four patients (168 eyes) were selected from January 2010 to February 2010 in Shanxi Eye Hospital who were scheduled to undergo LASIK surgery.CH and CRF values were compared to three corneal thicknesses (group A,550-643 μm; group B,500-549 μm; group C,450-499 μm).An Optical Reaction Analyzer (ORA) was used for measurements.Complete records were obtained from 40 patients (80 eyes) who visited regularly for 1 year and a comparative analysis of the corneal biomechanical characteristics were available for both the preoperative and postoperative periods (1,3,6, 1 months).A one-way ANOVA were used for data analysis using SPSS 13.0 software.Results The CRF and CH values for the three preoperative central corneal thickness groups were: 11.11±1.69 and 10.79±1.48, 9.83±1.39 and 9.87±1.29, 9.06±1.96 and 9.79±1.76. The differences were statistically significant (F=19.55,P＜0.01; F=8.54,P＜0.01).The differences in the CRF and CH values for the preoperative and postoperative periods were also statistically significant (F=102.88,P＜0.01; F=60.80, P＜0.01). But the CRF and CH values for the different postoperative periods were not statistically significant. Conclusion The CRF and CH values decreases with decreased corneal thickness. Corneal biomechanical characteristics are reduced significantly after LASIK surgery, but there is no change during the postoperative period after LASIK.More than 50％ of the entire corneal thickness is composed of the residual corneal stroma that is fairly stable and safe after LASIK. Key words: Keratomileusis,laser in situ; Biomechanics,corneal; Corneal resistance factor; Corneal hysteresis

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