The Clinical Utility Of Central Corneal Thickness Measured By Pentacam System

Purpose:To evaluate the application of Pentacam system to measure central corneal thickness(CCT)in normal and myopic subjects and the reliability of its measurements;to investigate the effects of age,gender, corneal curvature and eye side on CCT;to analyze the influence of ametropia on CCT.To investigate the difference among ultrasonic pachymetry,OrbscanⅡsystem and Pentacam system in CCT measurements and compare their repeatability.To study the relationships between CCT and intraocular pressure(IOP)measured by Goldmann applanation tonometer(GAT)in normal and myopic eyes and to analyse the effects of refractive status on CCT and IOP value measured by GAT.To compare the CCT of different types of glaucomatous eyes with CCT of normal eyes,then to evaluate the significance of CCT for glaucoma diagnosis.Methods:①195 eyes of 119 normal subjects and 148 eyes of 74 myopic individuals were included in the study.CCT was measured using Pentacam system and IOP using GAT,to derive the correction formula of CCT and IOP.②The data of 60 eyes in 30 normal subjects was selected randomly from Pentacam data bank.Choose one scheimpflug picture randomly and measure the CCT by three observers and by one observer at three different time to study the consistency of inter- and intra-observers with intraclass correlation coefficient(ICC).③The CCT of 60 eyes of 30 myopic subjects were measured by Pentacam,OrbscanⅡand ultrasound pachymetry,respectively.The data was analyzed using ANOVA,correlation and linear regression methods.④The CCT was measured using Pentacam system in 27 cases(54 eyes)with ocular hypertension(OHT), 30 patients(60 eyes)with primary open-angle glaucoma(POAG),and 31 patients(54 eyes)with primary angle-closure glaucoma(PACG).The results were compared with CCT of normal subjects.IOP of OHT and POAG were corrected using the equation formula this study and then evaluated the importance of CCT in the diagnosis of OHT and POAG.Results:①The mean CCT of normal eyes is(524.34±35.84)μm, and there were no significant difference between in the male, (524.51±36.29)μm and in the female,(524.17±35.38)μm(t=0.484, P=0.658);between in right eyes,(524.29±37.15)μm and in left eyes, (524.42±34.55)μm(t=0.59,P=0.962).There was a positive correlation between age and CCT in normal participants(r=0.190,P=0.002).There were no significant difference between in emmetropic eyes,(525.07±38.58)μm and in myopic eyes,(524.70±37.78)μm(t=-0.59,P=-0.962); the mean of CCT is(523.61±32.12)μm in mild myopia,(532.07±39.93)μm in moderate myopia,(515.83±39.87)μm in high myopia, respectively,and there was a significant difference between in emmetropia and in high myopia(t=2.288,P=0.020);significant positive correlation existed between CCT and diopter(r=0.128,P=0.025),and no significant correlation between CCT and corneal curvature(r_v=0.136, P_v=0.232;r_h=0.223,P_h=0.196).②The ICC of inter-and intra-observers of Pentacam system in measuring CCT were 0.996 and 0.995,respectively.③The mean CCT measured by Pentacam system,OrbscanⅡand ultrasound pachymetry were(515.70±32.96)μm,(534.27±33.88)μm and (535.32±34.88)μm,respectively.The mean CCT measured by Pentacam system was the least,and there were significant difference compared with ultrasound pachymetry(P=0.004)and OrbscanⅡ(P=0.003),respectively. While no significant difference existed between ultrasound pachymetry and OrbscanⅡ(P=0.920).The measurements of Pentacam system were significantly positive correlated with ultrasound pachymetry and OrbscanⅡ,and the coefficients of correlation between Pentacam system and ultrasound pachymetry,between Pentacam sysrem and OrbscanⅡare 0.979(P＜0.001),0.968(P＜0.001),respectively.The mean variances of Pentacam system,OrbscanⅡand ultrasound pachymetry of repetitive measurements in each eye were 3.96±3.85,6.58±3.62 and 5.26±2.89,respectively. The mean variances of Pentacam system was the least,and significant difference existed between Pentacam system and ultrasound Pachymetry(P=0.001),but there was no significant difference between Pentacam system and OrbscanⅡ(P=0.088).④In normal group,the mean value of IOP is(12.96±2.64)mmHg.There are significant positive correlation between IOP and CCT in both normal and myopic eyes,and the correlation index were 0.348(P＜0.001)and 0.347(P＜0.001), respectively;the effects of CCT for IOP were 1mmHg/40.00μm in normal eyes and 1mmHg/34.48μm in myopic eyes.The mean CCT of normal,PACG,POAG and OHT eyes were(524.34±35.84)μm,(528.36±32.98)μm,(532.89±31.68)μm and(574.68±29.04)μm,respectively. There were no significant difference among POAG(P=0.082), PACG(P=0.458)and normal eyes,and no significant difference between POAG and PACG(P=0.468).The CCT of OHT was the thickest (P＜0.001).Conclusion:The repeatability of Pentacam system is excellent. With aging,CCT mildly increased.CCT decreased with advancing degree of myopia,while IOP increased with advancing degree of myopia.CCT could significantly effect IOP,and refractive status had effects on the correlation between IOP and CCT.Compared with CCT of normal eyes, CCT of OHT eyes was thicker.There was no significant difference among the CCT of POAG,PACG and normal eyes.CCT played a significant role in OHT diagnosis.