Measurement of intraocular pressure using the NT-4000: a new non-contact tonometer equipped with pulse synchronous measurement function.
OBJECTIVE
NT-4000 (Nidek Co. Ltd., Gamagori, Japan) is a new non-contact tonometer (NCT) equipped with pulse synchronous measurement function that can measure intraocular pressure (IOP) synchronized with the ocular pulse. The purpose of this study was to evaluate the usefulness of NT-4000 in normal subjects and in patients with glaucoma and ocular hypertension.


METHODS
This study included 175 eyes of 175 subjects. Firstly, the IOP was measured using NT-4000 without the pulse synchronous measurement function (NTn). Secondly, the IOP at peak, middle, and trough phases of the pulse signal were measured using NT-4000 with the pulse synchronous measurement function (NTp, NTm, NTt, respectively). Additionally, the IOP was measured with Goldmann applanation tonometer (GT). The coefficient of variation (CV) of three readings in the NCT measurements was used to evaluate the intra-session reproducibility. Statistical comparisons were performed using Wilcoxon signed rank test and one-way analysis of variance with Scheffe's test. Linear regression analysis was used to calculate correlation coefficients. P values less than 0.05 were accepted as statistically significant.


RESULTS
The CV of NTn, NTp, NTm, and NTt were 6.4%, 5.5%, 4.9%, and 5.2%, respectively. The CV of NTp, NTm, and NTt were significantly smaller than that of NTn (P = 0.007, P < 0.001, P < 0.001, respectively). NTp was significantly higher than NTt (P = 0.038). GT was significantly correlated with NTn, NTp, NTm, and NTt (r = 0.898, P < 0.001; r = 0.912, P < 0.001; r = 0.908, P < 0.001; r = 0.900, P < 0.001, respectively).


CONCLUSIONS
NT-4000 can detect the fluctuation of IOP associated with the ocular pulse.
Yaoeda
Kiyoshi
K
Division of Ophthalmology and Visual Science, Graduated School of Medical and Dental Sciences, Niigata University, Niigata City, Niigata, Japan. yaoeda@med.niigata-u.ac.jp
Shirakashi
Motohiro
M
Fukushima
Atsushi
A
Funaki
Shigeo
S
Funaki
Haruko
H
Ofuchi
Nobutaka
N
Nakatsue
Tomoko
T
Abe
Haruki
H
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D005902:Glaucoma, Open-Angle / Q000175:diagnosis*; D006801:Humans; D007429:Intraocular Pressure; D008297:Male; D008875:Middle Aged; D009798:Ocular Hypertension / Q000175:diagnosis; D012016:Reference Values; D015203:Reproducibility of Results; D014065:Tonometry, Ocular / Q000295:instrumentation / Q000379:methods*