A Comparison of the Icare Pro Rebound Tonometer with Applanation Tonometry in Healthy Infants

Abstract

Aims: To study the accuracy and patient tolerability of the new Icare Pro rebound tonometer (ICPRO) compared with applanation tonometry in infants aged under 24 months. Methods: Prospective observational study of 50 consecutive patients with expected normal intraocular pressure (IOP). One eye of each patient was examined sequentially using an ICPRO and Perkins applanation tonometer (PAT) to obtain a single adequate IOP measurement for each device. Agreement was assessed using Bland-Altman analysis. An objective assessment of patient tolerance of IOP measurement was also recorded. Results: Mean age of patients was 12.6 months. Correlation of IOP measurement between PAT and ICPRO was moderate (r=0.384, p=0.0059). ICPRO underestimated IOP in 88% of cases: IOP was measured significantly lower with ICPRO (9.18±1.57 mmHg) compared to PAT (12.4±2.95 mmHg, p<0.001). The 95% limit of agreement (LOA) was -8.6 to 2.2 mmHg. Subgroup analysis showed ICPRO underestimated IOP most in infants over 12 months (mean: 4.8mmHg, 95% LOA:-9.5 to 0.2mmHg, p<0.0001). Measurement of IOP with the ICPRO was significantly better tolerated, causing distress and crying in 6%, compared to 62% with PAT (p<0.0001). IOP underestimation with ICPRO was significantly greater when infants were crying during PAT measurement (5.26±2.83) compared to when infants were not crying during PAT measurement (1.97±1.83, p<0.0001). Conclusions: ICPRO appears to be safe, tolerable and of adequate accuracy for the screening of IOP in infants. It consistently significantly underestimated IOP, therefore high or borderline IOPs measured with the ICPRO should be repeated with applanation tonometry to prevent missing cases of raised IOP.