Influence Factor Analysis Of Intraocular Pressure Measurement Before And After LASIK With Different Measurement Methods

Objective: To evaluate the changes of IOP measurement and coherence of Gold mann applanation tonometer and Noncontact tonometer after FS-LASIK and SBK.Methods: IOP of Goldmann applanation tonometer and Noncontact tonometer was measured in the 432 eyes of 219 consecutive patients who underwent FS-LASIK and SBK.Meanwhile,patient age,absolute value of preoperative spherical equ ivalent,preoperative radius of curvature,preoperative central corneal thickness,p reoperative IOP,ablation depth,ablation Rate were studied to determine whether they affect the underestimation of IOP.Results: The average values of preoperative IOP measured by Goldmann applana tion tonometer and Non-contact tonometer were 15.531 mm Hg and 15.529 mm Hg,and there was no statistical significant difference betwen them(p = 0.972),however Bland-Altman graphs showed remarkable disagreement which could be part ially explained by the correlation between preoperative central corneal thickness with D-value of IOP of Goldmann applanation tonometer and Non-contact tonom eter(r = 0.31,p < 0.001).It is general that Goldmann applanation tonometer measurements is higher in a thinner cornea((CCT< 510?m)and lower in a thicker cornea(CCT > 580?m),It was statistically significant difference betwen the reduction of IOP measurement of Goldmann applanation tonometer and Non-contact tonometer after FS-LASIK which were 3.17+/-2.38 mm Hg and 6.25+/-2.40 mm Hg compared with preoperative measurements.It was also statistically significantly different between the reduction of IOP measurement of Goldmann applanation tonometer and Non-contact tonometer after SBK which were 2.74+/-1.84 mm Hg and 5.62+/-1.85 mm Hg compared with preoperative measurements.The reduction of IOP measured by Non-contact tonometer was higher than the IOP measured by Goldmann applanation tonometer after FS-LASIK and SBK.There was a positive correlation between the reduction of IOP measurement of Goldmann applanation tonometer with the absolute value of spherical equivalent,preoperative applanati on tonometer measurements,preoperative centre corneal thickness,ablation depth,ablation rate(p<0.05)and a no-correlation with age,preoperative radius of curva ture(p >0.05)after FS-LASIK.then,we would get the regression formula using stepwise regression analysis to eliminate collinearity relationship : ?IOP-GAT = 0.635 ×preoperative IOP-GAT + 15.633 × ablation rate-8.554(R2 = 0.50,F = 204.16,p < 0.001);meanwhile,there was a positive correlation between the reduction of IOP measurement of Non-contact tonometer with age,the absolute value of spherical equivalent,preoperative non-contact tonometer measurements,preope rative centre corneal thickness,ablation depth,ablation rate(p<0.05)and a no-corr elation with preoperative radius of curvature(p >0.05)after FS-LASIK.The regr ession formula was: ?IOP-NCT=0.603× preoperative IOP-NCT + 20.493× ablation rate-5.994(R2=0.65,F=274.92,p<0.001).There was a positive correlatio n between the reduction of IOP measurement of Goldmann applanation tonometer with the preoperative Goldmann applanation tonometer measurements(p<0.05)and a no-correlation with age,the absolute value of spherical equivalent,preoperative radius of curvature,preoperative centre corneal thickness,ablation depth,ablation rate(p >0.05)after SBK,the regression formula was : ?IOP-GAT = 0.525 ×preoperative IOP-GAT-5.327(R2 = 0.33,F = 63.49,p < 0.001);meanwhile,there was a positive correlation between the reduction of IOP measurement of Noncontact tonometer with the absolute value of spherical equivalent,preoperative non-contact tonometer measurements,ablation depth,ablation rate(p<0.05)and a negative correlation with preoperative radius of curvature(p<0.05)and a no-correlati on with age,preoperative centre corneal thickness(p >0.05)after SBK.The regression formula was: ?IOP-NCT=0.566× preoperative IOP-NCT + 21.501× ablatio n rate-6.142(R2=0.48,F=57.90,p<0.001).Conclusion: Bland-Altman graphs shows remarkable disagreement between IOP of Goldmann applanation tonometer and Noncontact tonometer,although there is no statistical difference between the mean value of them.Besides,the corneal thic kness still need to be refereed.Both of the measurement values of the IOP were significantly decreased after FS-LASIK and SBK,but the reduction of Non-contact tonometer measurement is much higher,and preoperative IOP is the most im portant parameter that affects an underestimation of IOP after surgery,eyes with a higher true IOP have a larger underestimation of the IOP after LASIK for my opia.