Validity and limitations of the Nidek NT-4000 non-contact tonometer: a clinical study

Using Goldmann applanation tonometry (GAT) as a gold standard, we evaluated the accuracy of Nidek NT-4000 pneumotonometry (NPT) in adults without corneal disease. Bland and Altman analysis of serial intra-ocular pressures (IOPs) measured with NPT and GAT in 10 healthy subjects revealed that the repeatability coefficients for the two methods were similar. NPT, GAT and ultrasonic pachymetry were then performed in 100 patients. Bland and Altman analysis showed that NPT yielded significantly higher readings than GAT [mean biases for right and left eye measurements were 1.37 mmHg (95% limits of agreement: -3.02-5.76) and 1.17 mmHg (95% limits of agreement: -2.76-5.11) respectively] and was more affected by corneal thickness variations. For detection of IOPs >= 21 mmHg, NIPT displayed very high sensitivity (0.90) and good specificity (0.95). NPT may be useful in screening and clinical settings but borderline-high IOP readings should be confirmed with GAT.