Comparison of intraocular pressure measurements using four different devices and its relation with central corneal thickness in glaucoma patients

ABSTRACT Abdulgani Kaymaz, Comparison of Intraocular Pressure Measurements Using Four Different Devices and Its Relation with Central Corneal Thickness in Glaucoma Patients. The Master Thesis, Bolu, 2013. Glaucoma is an optic neuropathy associated with intraocular pressure (IOP) elevation, optic nerve head (ONH) pitting-atrophy and progressive visual field loss. Elevated IOP is the most important indicator in the diagnosis, classification and follow-up of glaucoma. Therefore, accurate and reliable measurement of IOP is needed. Functional loss of vision that is occurred during the course of glaucoma can be detected by automated perimetry. Significant cell loss precede the detectable visual field (GA) in glaucoma patients. Therefore, researchers has been investigated newer and more reliable methods of early diagnosis of glaucoma. In our study, we compared the IOP measurements using Goldmann applanation tonometry (GAT), Tonopen tonometer (Tonopen Avia) and noncontact tonometer (NCT) (Canon TX-10 and TX-20P) and the relationship with IOP measured by these devices and central corneal thickness (CCT) in glaucoma patients. The study included 67 patients [37 male (55.2%) and 30 women (44.8%)] with a mean age of 64.09±8.017. 46 (68.7%) patients had primary open angle glaucoma (POAG) and 21 (31.3%) patients had pseudoexfoliative glaucoma (PEG). In our study, the IOP values that were measured using NCT TX-10 and TX-20P IOPstd (IOP measurement of Canon TX-20P, which was not corrected according to central corneal thickness) had statistically moderate and significant correlation with CCT (respectively, TX-10 r = 0.285, p = 0.019, TX-20P IOPstd r = 0.326 p = 0.007). The IOP measurements of NCT TX-20P IOPcor (IOP measurement of Canon TX-20P, which was corrected according to central corneal thickness), Tonopen and GAT did not correlate significantly with CCT (TX-20P IOPcor p=0,825, Tonopen p=0,980 ve GAT p=0,740). There was no statistically significant difference between the IOP values that were measured using GAT and Tonopen (p = 0.705) and TX-10 and Tonopen (p = 0.104). As a result, IOP measurements of NCT and Tonopen were higher than the IOP measurements of GAT. Although IOP measurements of Canon TX-10 and Tonopen were slightly higher than GAT (approximately 1.5 mmHg and 1.8 mmHg, respectively), 95% confidence interval value had clinically unacceptable amplitude (5.5 mmHg and 5.6 mmHg, respectively). The IOP measurements of Canon TX-20P IOPstd and TX-20P IOPcor gives considerably higher than GAT (respectively about 3 mmHg and 3.5 mmHg) and these values were not clinically acceptable. There was no relationship between CCT and the IOP measurement using GAT, Tonopen and Canon TX-20P IOPcor (p> 0.05). A moderate positive correlation was found between CCT and IOP measurement using NCT Canon TX-10 and NCT Canon TX-20P IOPstd (r=0.285, p=0.019 and r=0.326, p=0.007, respectively). Keywords: Glaucoma, Goldmann applanation tonometer, tonopen tonometer, noncontact tonometry, central corneal thickness.