A comparison of four methods of tonometry: method agreement and interobserver variability

Abstract

Aim: To compare the inter-method agreement in intraocular pressure (IOP) measurements made with four different tonometric methods. Methods: IOP was measured with the Goldmann applanation tonometer (GAT), Tono-Pen XL, ocular blood flow tonograph (OBF), and Canon TX-10 non-contact tonometer (NCT) in a randomised order in one eye of each of 105 patients with ocular hypertension or glaucoma. Three measurements were made with each method, and by each of two independent GAT observers. GAT interobserver and tonometer inter-method agreement was assessed by the Bland-Altman method. The outcome measures were 95% limits of agreement for IOP measurements between GAT observers and between tonometric methods, and 95% confidence intervals for intra-session repeated measurements. Results: The mean differences (bias) in IOP measurements were 0.4 mm Hg between GAT observers, and 0.6 mm Hg, 0.1 mm Hg, and 0.7 mm Hg between GAT and Tono-Pen, OBF, and NCT, respectively. The 95% limits of agreement were smallest (bias ¡2.6 mm Hg) between GAT observers, and larger for agreement between the GAT and the Tono-Pen, OBF, and NCT (bias ¡6.7, ¡5.5, and ¡4.8 mm Hg, respectively). The OBF and NCT significantly underestimated GAT measurements at lower IOP and overestimated these at higher IOP. The repeatability coefficients for intra-session repeated measurement for each method were ¡2.2 mm Hg and ¡2.5 mm Hg for the GAT, ¡4.3 mm Hg for the Tono-Pen, ¡3.7 mm Hg for the OBF, and ¡3.2 mm Hg for the NCT. Conclusions: There was good interobserver agreement with the GAT and moderate agreement between the NCT and GAT. The differences between the GAT and OBF and between the GAT and Tono-Pen probably preclude the OBF and Tono-Pen from routine clinical use as objective methods to measure IOP in normal adult eyes.

Evaluation of agreement between intraocular pressure measurements using Goldmann applanation tonometry and Goldmann correlated intraocular pressure by Reichert's ocular response analyser

“…The authors presented estimates of IOP differences between tonometry methods at various levels of IOP, as in the current investigation. Of note, at 15 mm HgFapproximately the mean IOP in the current studyFestimated GAT-IOPg agreement in this study was superior to agreement between GAT and all other IOP measurement techniques considered by Tonnu et al Moreover, this study determined a mean difference of 0.1 mm Hg between GAT and IOPg values, compared with 0.7 mm Hg between GAT and NCT in the study by Tonnu et al 25 In addition, in two separate studies, Jorge et al 27 demonstrated a difference of 0.1 mm Hg between GAT and NCT values among normal 26 and glaucomatous subjects using the same NCT machine. However, using a different NCT machine (from the same manufacturer) to study the same cohort of normal subjects, the investigators reported a mean GAT-NCT difference of 0.8 mm Hg.…”

The effect of orbital decompression surgery on refraction and intraocular pressure in patients with thyroid orbitopathy

“…30 Goldberg 31 commented that in patients with TO, central corneal thickness is a confounder for accurate tonometry, and that apparent changes in IOP could be simply due to increases in CCT. By contrast, we found that orbital decompression did not significantly affect CCT, so would dispute this theory, but acknowledge that CCT is important in determining whether or not to commence ocular anti-hypertensive therapy.…”

Tonometry: an overview

“…Several authors have demonstrated that tonopen tends to overestimate low IOPs and underestimate high IOPs [7,8,9,10]. Others have concluded that there is no such variation [11,12].…”