Intervariability in IOP measurement by using GAT, rebound tonometer and NCT in glaucoma patients

Abstract

Context: Intraocular pressure (IOP) remains the only treatable risk factor in the management of glaucoma patients. Therefore, an accurate IOP measurement is essential for ophthalmic examination. The accuracy of IOP measurement can be affected by factors like central corneal thickness (CCT), astigmatism and biomechanics of the cornea. The purpose of our study was to assess the agreement of IOP measured by Goldmann applanation tonometer (GAT), iCare and non-contact tonometer (NCT) in different IOP group. Aim: To compare IOP measured by NCT, iCare and GAT in different IOP groups. Study Design: Cross-sectional study. Methods and Material: 201 eyes of 101 subjects were enrolled in this study. The patients were divided into three groups: group 1: <10 mmHg, group 2: 11–20 mmHg and group 3: 21–30 mmHg. IOP measurement was done in NCT– iCare–GAT sequence. CCT values were obtained by pachymetry and scatter plot was performed. Results: The IOP intervariability In group 1 , NCT–GAT [r = 0.30, P = 0.238, intraclass correlation coefficient (ICC) = 0.37], iCare–GAT (r = 0.53, P = 0.028 ICC = 0.65); group 2 NCT–GAT (r = 0.74, P < 0.001, ICC = 0.85), iCare–GAT (r = 0.76, P < 0.001, ICC = 0.84); group 3 NCT vs GAT (r = 0.55, P = 0.001, ICC = 0.70), iCare vs GAT (r = 0.52, P = 0.002, ICC = 0.66). IOP measurements of the three methods were significantly correlated with CCT. Bland–Altman analysis showed significant agreement between the three devices (P < 0.01). Conclusions: iCare showed a better agreement with GAT when compared over a wide range of IOP. The three tonometers were similar in a low IOP range while there was an overestimation with NCT in higher IOP groups. NCT seemed to be influenced more by CCT followed by GAT and iCare.