Test-Retest Variability of Intraocular Pressure and Ocular Pulse Amplitude for Pascal Tonometer : A Multicenter Study

Purpose:To assess the test-retest repeatability of intraocular pressure (IOP) and ocular pulse amplitude (OPA) measurements by Pascal tonometer (PT) and evaluate possible influential factors. Methods:The study included 200 consecutive subjects (100 normal, 100 POAG) from 5 different Italian clinics. IOP was measured once by Goldmann applanation tonometer (GAT) and twice by PT (PT1, PT2) in randomized sequence. Difference between PT1 and PT2, OPA1 and OPA2, and GAT and PT1 and 2 was assessed by t-test. The percentage of PT2 and OPA2 falling respectively within ±1.0 mmHg from PT1 and within ±0.5 mmHg from OPA1 was calculated. Regression analysis was used to assess the influence of demographic factors (age, sex), ophthalmic data (diagnosis, refraction), and ocular biometrics (corneal curvature; central corneal thickness, CCT; axial length; anterior chamber depth). Results:PT1 was 0.7±1.4 mmHg higher than PT2 (P<0.001); OPA1 was 0.1±0.6 mmHg higher than OPA2 (P=0.16). Results were not influenced by randomization test order. Test-retest variability was 48% for IOP readings taken with PT, and 26% for OPA. PT readings were 3.5±2.5 mmHg higher than GAT (P<0.001). Demographic and biometric factors (i.e. CCT; R2=0.07, P=0.48) did not significantly effect results; however, OPA tended to be higher in glaucoma patients (3.9±1.2 vs. 2.8±1.0, P=0.05). Conclusions:Tonometry readings taken with PT tended to be overestimated compared to GAT. PT test-retest variability was moderate for IOP and good for OPA. PT measurements were not effected by demographic or ocular factors.