The effects of central corneal thickness and diopter on applanation tonometry measurements

Objective To investigate the relationship between CCT and IOP by GAT and to analyse the effect of refractive status on CCT and IOP by GAT measurements. Methods One hundred and twenty-one normal subjects(199eyes) and 81 myopic patients (159 eyes) were included in this study.In each eye,CCT was measured with an OCT system (STRATUS OCT,OCT3) and IOP with GAT.CCT and IOP readings of each group were compared to estimate the effect of CCT on IOP measurement by GAT. Results There was no significant difference of mean CCT between normal subjects (525.05 ± 32.83μm) and persons with myopia (524.85 ± 29.76μm). The mean IOP by GAT was 12.9 ± 2.26 mmHg for normal subjects and 14.23 ± 2.54 mmHg for persons with myopia and had significant difference between two groups (t = -5.139,P0.001).There was positive correlation with CCT and IOP by GAT measurements in both groups (r=0.317,P0.001 for normal and r=0.341,P=0.001 for myopia).High myopic eyes had thinner CCT and the myopic diopter was negatively correlated with IOP (r=-0.296,P0.001),IOP increased 1mmHg with per-4.05D increase. Conclusions IOP with GAT can be effected by CCT and influenced by refractive status.In high myopic eyes,IOP by GAT is advised to be corrected with correction equation from myopic eyes.