Relationship Between Ocular Pulse Amplitude Examined by Dynamic Contour Tonometer and Intraocular Pressure or Central Corneal Thickness

Abstract

Purpose:: Ocular pulse amplitude (OPA) has been shown to have a significant correlation with intraocular pressure (IOP) and a negative correlation with axial length. OPA has also been thought to rely on the elastic properties of the ocular shell. This study was conducted to evaluate the differences between primary open angle glaucoma (POAG) and primary angle closure glaucoma (PACG) in the correlation between OPA and IOP (Exp-1) or central corneal thickness (CCT) (Exp-2) using a Dynamic Contour Tonometer (DCT).

Methods:: In Exp-1, we performed a cross-sectional survey designed to measure DCT in 318 eyes of 186 glaucoma patients (pts) (217 eyes / 130 pts, POAG; 101 eyes / 56 pts, PACG (mean age: 63.9±12.5 years)) at the Glaucoma Clinic in Kyoto Prefectural University of Medicine. Patients with a history of laser treatment or surgery were excluded. Single regression analysis was performed and compared between the POAG and PACG groups in the condition of IOP as x-axis and OPA as y-axis. Seventeen patients from Exp-1 were selected for Exp-2, all patients matching the following inclusion criteria: both eyes were examined and received the same kind of eye drops, axial lengths of each eye were matched within 0.6 mm, OPA had a difference of more than 0.5 mmHg between the right and left eyes. Mean IOP and CCT were calculated and compared between those eyes of higher OPA (OPA_H) and lower OPA (OPA_L) using the Student’s t test.

Results:: There was a positive correlation between OPA and IOP in both groups (0.10 mmHg OPA / mmHg IOP, r=0.44, p<0.01 (POAG) and 0.16 / mmHg IOP, r=0.52, p<0.01 (PACG)), and the slope of PACG was significantly higher than that of POAG (p=0.028). Not only mean IOP, but also mean CCT of OPA_H showed no significant differences (p = 0.81 for IOP, 0.84 for CCT) from those of OPA_L (OPA_H: 18.4±3.1, OPA_L: 18.1±3.4 mmHg for IOP, OPA_H: 531±45.4, OPA_L: 534±51.1 micrometer for CCT) among those eyes of the matched axial length.

Conclusions:: The OPA readings in both POAG and PACG examined by DCT showed a significant positive correlation with IOP, while a different trend was observed between the two glaucoma types. CCT showed little contribution to the OPA differences between the two eyes of matched axial length.

Keywords: intraocular pressure • optical properties