Agreement between rebound (Icare ic200) and applanation tonometry (Perkins) in patients with primary congenital glaucoma

Abstract

Purpose To examine agreement between intraocular pressure (IOP) measurements made using the rebound tonometer Icare ic200 (RT200) and the Perkins handheld applanation tonometer (PAT) in patients with primary congenital glaucoma (PCG). The impacts of several covariables on measurements using the two devices were also assessed. Materials and Methods Intraocular pressure measurements were made in a single session in 86 eyes of 86 patients with PCG (46 under anaesthesia, 40 in the office). The order was RT200 then PAT. The variables age, central corneal thickness (CCT), corneal state and anaesthesia were recorded in each patient. Data were compared by determining interclass correlation coefficients (ICC) for each tonometer and representing the differences detected as Bland–Altman plots. Effects of covariables were assessed through univariate and multivariate regression. Results Mean IOP difference between tonometers (RT200 minus PAT) was 1.26 mmHg (95%: 0.22–2.31). Absolute agreement (ICC) was 0.73 (95% CI: 0.62–0.82). Lower and upper limits of agreement (95%) were −8.06 mmHg (95% CI: −9.87 to −6.25) and 10.59 mmHg (95% CI: 8.77–12.40), respectively. The tonometers showed systematic differences (a = −4.63 mmHg; 95% CI: −9.11 to −1.44) and proportional differences; for each mmHg increase in PAT‐IOP, the RT200 reading increased by 1.28 mmHg (b = 1.28; 95% CI: 1.12–1.53). None of the variables tested as predictors were able to explain differences between the tonometers. Conclusions Despite the good overall agreement between both tonometers, caution should be taken in high values of IOP, considering the interchangeability of its readings as systematic and proportional differences appear to exist between both methods.

Effects of Corneal Biomechanical Properties on Rebound Tonometry (Icare200) and Applanation Tonometry (Perkins) Readings in Patients With Primary Congenital Glaucoma

“…This is consistent with results obtained in our preliminary study using IC200 6. Mean difference between IOP Ic200 and Perkins IOP readings was 1.26 mm Hg, an upper limit of agreement of −8.06 mm Hg and a lower limit of agreement of 10.59 mm Hg.…”

“…In our preliminary study, 6 systematic and proportional differences between IC200 and Perkins IOP readings were found. These differences were higher in high values of IOP, especially in PCG patients.…”

“…Nakakura et al14 also reported this underestimation of IOP by IC100 compared with ICare TA01 and Goldmann tonometry. This controversy observed in the literature could be explained by the Passing-Bablok regression equation recently reported: IC200-IOP=−4.63+1.28 Perkins-IOP 6. So, higher values of Perkins readings result on higher readings of IC200 IOP, however, readings using IC200 could be lower, when Perkins IOP is lower than 16 mm Hg.…”