[Clinical evaluation of the dynamic rebound tonometer Icare]

The Icare dynamic tonometer (impact or Rebound tonometry) is a new tonometer based on making a moving object collide with an eye and on monitoring the motion parameters of this object following contact. The purpose of this study was to assess intra- and interobserver variability of IOP measurements with the Icare and their correlations with Goldmann applanation tonometry (GAT) and central corneal thickness (CCT).

A prospective study including three groups of patients: group 1 (50 normal subjects), group 2 (50 patients with OHT or POAG and GAT IOP>22 mmHg), and group 3 (38 glaucomatous patients with GAT IOP< or =22 mmHg). In group 1, three consecutive IOP measurements were taken by three distinct observers with Icare followed by three GAT measurements by the same clinician. In group 2, the same procedure was followed from patients 1 to 25 and the reverse sequence from patients 25 to 50 after a 10-min break. In group 3, only one clinician took three GAT measurements followed by three Icare measurements after a 10-min break to exclude a tonographic effect in eyes with statistically normal-range IOPs.

: In group 1, intraobserver variability was about 6% for each observer (NS). There was no learning curve effect. The interobserver variation coefficient was 6.4%. Icare overestimated IOP compared to GAT (mean difference, 1.5-2.2 mmHg) (p<0.001). Icare IOP was 23.4 mmHg for observer 1 when GAT was 22 mmHg (95% individual CI, 18-28.9 mmHg). In group 2, intraobserver variation coefficients of the IOP ranged from 5% to 5.4% (NS). Icare overestimated IOP by mean 0.84 mmHg compared with GAT. In group 3, mean IOP was not different between Icare and GAT. Icare IOP of 20.7 mmHg corresponded to a value of 22 mmHg using GAT. In this group, correlations between CCT and IOP measurements were higher for Icare than for GAT (p=0.062).

Icare measures IOP in an unanesthetized sitting patient in a very brief time. Patient's minimal cooperation is needed. As long as the device is correctly positioned, the learning curve is short. Icare gives reproducible IOP measurements. Intra- and interobserver variability of IOP measurements are close to those of GAT. Icare overestimates IOP measurements an average 1.5 mmHg compared with GAT. Whatever the IOP level, Icare IOP measurements are well correlated with GAT. To a greater extent than for GAT, the reliability of IOP measurements is influenced by CCT. This tonometer can be used as a screening device for ocular hypertension as long as CCT measurements can be taken.