Abstract
PurposeTo investigate whether corneal thickness parameters measured by optical coherence tomography (OCT), such as central corneal thickness (CCT), central corneal stromal thickness (CCST), and central corneal epithelial thickness (CCET), influence the intraocular pressure (IOP) difference measured by Goldmann applanation tonometry (GAT) and non-contact tonometry (NCT).MethodsIn total, 50 eyes from 50 subjects without glaucomatous defects were included in this retrospective, cross-sectional study. We measured IOP using GAT and NCT and calculated the difference between the two methods. CCT was measured by a Cirrus HD-OCT device using anterior segment imaging. The basement membrane of the epithelium, which was seen as a high-reflection line in the OCT image, was taken as a reference line to measure CCST and CCET.ResultsThe mean IOP measured by GAT and NCT was 16.7 ± 3.0 and 18.1 ± 3.8 mmHg, respectively. The mean IOP difference was 1.5 ± 1.7 mmHg, and the IOP measured by NCT was 8.4% ± 11.3% higher than that measured by GAT. The CCET and CCST were 57.9 ± 5.6 and 501.7 ± 33.8 μm, respectively. CCT showed a positive correlation with both GAT IOP (r = 0.648, P < 0.001) and NCT IOP (r = 0.676, P < 0.001). Although CCST showed a significant correlation with GAT IOP and NCT IOP, CCET did not. The difference between GAT IOP and NCT IOP increased with CCT (r = 0.333, P = 0.018), and CCET was positively correlated with the IOP difference between GAT and NCT (r = 0.435, P = 0.002).ConclusionsIOP increased with greater CCT, and CCST seemed to have a more important role than CCET. CCET also increased with greater CCT, and this may be a possible explanation for the increasing difference in IOP between GAT and NCT with increasing CCT.
Highlights
Elevated intraocular pressure (IOP) has been determined to be closely related to the development of glaucoma and the progression of glaucomatous damage, based on some well-known clinical trials.[1,2,3] precise measurement of IOP is important in the management of glaucoma, as well as in monitoring its progression
The mean IOP difference was 1.5 ± 1.7 mmHg, and the IOP measured by noncontact tonometry (NCT) was 8.4% ± 11.3% higher than that measured by Goldmann applanation tonometry (GAT)
central corneal stromal thickness (CCST) showed a significant correlation with GAT IOP and NCT IOP, central corneal epithelial thickness (CCET) did not
Summary
Elevated intraocular pressure (IOP) has been determined to be closely related to the development of glaucoma and the progression of glaucomatous damage, based on some well-known clinical trials.[1,2,3] precise measurement of IOP is important in the management of glaucoma, as well as in monitoring its progression. The most accurate method for this is direct IOP measurement by cannulation, it is impossible to conduct this procedure in a glaucoma clinic. Based on its own principle that GAT measures the force needed to flatten a given area of the cornea, GAT is inevitably affected by central corneal thickness (CCT).[4] In the cannulation study by Ehlers et al.[5], GAT errors were found to be as large as 5 to 6 mmHg in otherwise normal eyes, and GAT appeared to be most accurate with a CCT of 520 μm. Thicker corneas resulted in a higher IOP estimate, while thinner corneas resulted in estimated IOPs lower than the actual value
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