Analysis of intraocular pressure measurement and the influencing factors after small incision lenticule extraction

Abstract

To discuss the accuracy of intraocular pressure (IOP) values measured after small incision lenticule extraction (SMILE), analyze the corneal biomechanical influencing factors of IOP measurement before and after SMILE, and regress the equation of IOP variation for estimating actual IOP. In this clinical controlled study, 116 eyes (60 patients) with myopia and myopic astigmatism undergoing SMILE surgery were included. The ocular response analyzer, noncontact tonometer (NCT), and Pentacam system were used to measure the IOP preoperatively and at 3 months postoperatively, acquiring IOPg, IOPcc, NCT, Ehlers, Shah, Dresden, Orssengo, and Kohlhaas. The eight IOPs before and after surgery were analyzed with the paired t-testing. The Pearson correlation coefficient and Spearman correlation coefficient were used to evaluate the relationship between preoperative and postoperative IOPs and influencing factors. The regression analysis of IOP variation ΔNCT and influencing factors was performed with the multiple linear regression analysis. The Shah program in Pentacam showed no difference between preoperative and postoperative IOP values (t=-0.08, P=0.940). There was significant difference in the other IOPs before and after SMILE (P<0.001). The preoperative IOPg, IOPcc, and NCT were correlated with the preoperative CRF (r=0.674, 0.248, 0.710,P<0.01). The preoperative IOPg, NCT, Ehlers, and Shah were correlated with the preoperative CCT (r=0.260, 0.259, -0.418, -0.245,P<0.01). A moderately positive correlation was shown between the preoperative and postoperative IOPs (r≥0.5,P=0.000). The postoperative IOPg, Ehlers, Shah, and Dresden were correlated with the postoperative CCT (P<0.05). The postoperative IOPg, NCT, Orssengo/Pye, and Kohlhaas were correlated with the postoperative CRF (r=0.707, 0.549, 0.276, 0.346,P<0.01). The postoperative IOPg, IOPcc, NCT, Ehlers, and Shah were correlated with the postoperative CH (r=0.296, -0.366, 0.270,-0.349,-0.197,P<0.05). The regression equation of IOP variation ΔNCT and influencing factors was ΔNCT=-4.618+ 0.389NCTpre-0.431SC (SC was the algebraic sum of sphere and cylinder,R(2)=0.366, P=0.000). The evaluation of IOP values after SMILE should not only take the preoperative IOP and postoperative CCT into consideration, but also the corneal biomechanics which may affect the postoperative IOP. IOPcc and Pentacam corrective IOPs are relatively reliable after SMILE. Among the five correction methods of Pentacam system, Shah program can be used as the first choice for correct IOP after SMILE. The regression equation of the postoperative corrected NCT, NCTpost corrected=NCTpost measured +0.389NCTpre-0.431SC-4.618, may be used to evaluate the real postoperative IOP in clinical practice.