Effects of corneal biomechanical properties on rebound tonometry (Icare200) and applanation tonometry (Perkins) readings in patients with primary congenital glaucoma

Objective: To assess the influence of corneal biomechanics on intraocular pressure (IOP) measurements made with the Icare200 (IC200) rebound tonometer and the Perkins hand-held applanation tonometer in patients with primary congenital glaucoma (PCG). \nMaterials and methods: 40 PCG patients and 40 healthy controls, age and gender-matched, were recruited. IOP was measured with the Ocular Response Analyzer (IOPc, IOPg), Icare200 and Perkins. The variables age, IOP, corneal hysteresis (CH), corneal resistance factor (CRF), central corneal thickness (CCT), best corrected visual acuity, spherical equivalent, medications and glaucoma surgeries were recorded for each subject. Uni and multivariate analysis were used to detect effects of variables on IOP measurements. \nResults: Mean CCT was 545.65±71.88 μm in PCG vs. 558.78±27.58 μm in controls (p=0.284). CH and CRF were significantly lower in PCG group than in control group: mean CH 8.11±1.69 mmHg vs. 11.15±1.63 mmHg (p<0.001), and mean CRF 9.27 ± 2.35 mmHg vs. 10.71 ± 1.75 mmHg (p=0.002). Mean differences between IOP IC200-Perkins were 0.79 ± 0.53 mmHg in PCG vs. 0.80 ± 0.23 mmHg in controls (p<0.001) and mean differences IC200-IOPc were -0.89 ± 5.15 mmHg in PCG (p<0.001) vs. 1.60 ± 3.03 mmHg in controls (all p<0.009). Through multivariate analysis, CRF showed \npositive association and CH negative association with IOP measured with Perkins or IC200 in both subject groups. No association was detected for CCT, age or gender. \nConclusion: CH and CRF were identified as the main factors interfering with IOP measurements made with both tonometers in patients with PCG and healthy controls.