The validity of a new noncontact tonometer and its comparison with the Goldmann tonometer

Purpose. This study compared a new noncontact tonometer (NCT), the Nidek NT-4.000 (Nidek Co., Ltd., Aichi, Japan), with a pulse detection feature; an earlier model, the Nidek NT-2000, without this pulse detection facility; and Goldmann tonometry. Methods. Thirty-one young subjects had their intraocular pressure (IOP) in one eye randomly measured by two NCT's, followed by a Goldmann tonometer. The pulse detection mode used by the NT-4000 included synchronizing the IOP with the peak of the pulse (P-P), the middle of the pulse (P-M), or the bottom of the pulse (P-B). The order of measurements from these three modes was also random. Three consecutive readings were obtained from each mode/tonometer, and the mean was used for analysis. Results. Goldmann tonometry demonstrated the smallest variation from consecutive measurements (coefficient of variation, <4%), followed by the NT-4000 (coefficient of variation, <5% in various modes) and the NT-2000 (coefficient of variation, >5%). For the NT-4000, the mean IOP decreased from the highest in the P-P mode (16.1 mm Hg) to the lowest in the P-B mode (14.7 mm Hg), with the P-M mode in the middle. A significant difference was found among the IOP readings using the NT-4000 (in various modes), NT-2000, and Goldmann tonometry (repeated-measures analysis of variance, p < 0.01). More than 80% of the results from the NT-4000 were within 3 mm Hg of those from the Goldmann tonometry. Conclusions. The pulse detection feature from this new NCT could capture and monitor pulse waves, thus reducing the variations in the consecutive measurements. The NT-4000 also performed better than the NT-2000 when compared with the Goldmann tonometry.