Intraocular pressure and pulse rate measurements by the OBF tonograph — comparison to reference instruments

Aims: To investigate the effect of central corneal thickness and corneal curvature on intraocular pressure measurements using the pulsatile ocular blood flow tonograph and the Goldmann applanation tonometer, and to assess the agreement between the pulsatile ocular blood flow tonograph and the Goldmann applanation tonometer in intraocular pressure measurement. Methods: 479 subjects underwent intraocular pressure measurements with the Goldmann applanation tonometer and the pulsatile ocular blood flow tonograph. Of these, 334 patients underwent additional measurement of central corneal thickness with an ultrasonic pachymeter and corneal curvature measurement with a keratometer. Results: The intraocular pressure measurements obtained with both the Goldmann applanation tonometer and the pulsatile ocular blood flow tonograph varied with central corneal thickness and mean keratometric reading. Intraocular pressure measured using the Goldmann applanation tonometer increased by 0.027 mm Hg per mm increase in central corneal thickness. Intraocular pressure measured using the pulsatile ocular blood flow tonograph increased by 0.048 mm Hg per mm increase in central corneal thickness. For an increase of 1 mm of mean corneal curvature there was rise in intraocular pressure of 1.14 mm Hg measured by the Goldmann applanation tonometer and of 2.6 mm Hg measured by the pulsatile ocular blood flow tonograph. When compared to the Goldmann applanation tonometer, the pulsatile ocular blood flow tonograph underestimated at low intraocular pressure and overestimated at higher intraocular pressure. Conclusion: Central corneal thickness and corneal curvature affected measurements obtained with the pulsatile ocular blood flow tonograph more than they affected measurements obtained with the Goldmann applanation tonometer.

Section: Discussionsupporting

confidence: 82%

Effect of corneal parameters on measurements using the pulsatile ocular blood flow tonograph and Goldmann applanation tonometer

Gunvant

2004

“…*Oculab Tono-Pen; **Mentor Tono-Pen XL; ***Bio-Rad Tono-Pen XL; OBF tonograph (OBF Labs). ÀOverall value: tonometer overestimates GAT at low IOPs and underestimates at high IOPs.Overall value: tonometer underestimates GAT at low IOPs and overestimates at high IOPs.GAT/OBF comparisons On average, the OBF slightly underestimated IOP measurements by the GAT(table 1), in agreement with Yang et al8 In contrast, an overestimation by the OBF was reported by Bafa et al 9 and Bhan et al19 The 95% limits of agreement were similar to previous findings (table 4). The OBF underestimated GAT IOP by 2.6 mm Hg at 15 mm Hg and overestimated GAT IOP by 2.6 mm Hg at 25 mm Hg (table 3).…”

supporting

confidence: 88%

“…Various studies have compared one or two of these instruments with the GAT, [5][6][7][8][9][10][11][12] and most studies have not compared inter-tonometer agreement with GAT interobserver agreement (variation in measured IOP arise from both intertonometer and interobserver differences). To our knowledge, a broad comparison of all instruments in the same group of patients has not been published.…”

mentioning

confidence: 99%

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

Tonnu

2005

193

149

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.

“…13 25 26 It is claimed by the manufacturers to be unaffected by corneal thickness based on the measurement of IOP using a similar instrument before and after excimer photorefractive keratectomy. 26 27 In the current study, linear regression analysis of the three different instruments showed that IOP readings by the OBF pneumotonometer were most affected by the variations in CCT.…”

Section: Discussionmentioning

confidence: 99%

“…10 Recent studies have shown that the OBF pneumotonometer produces similar results to both manometric and Goldman applanation techniques. [11][12][13][14] However, other workers have questioned its usefulness in a clinical environment owing to its poor intra-individual repeatability. 15 The aim of this study was to determine the effect of CCT on IOP measurements made using the Goldmann applanation tonometer, Tono-Pen, and the OBF pneumotonometer in patients with keratoconus (KC), Fuchs' endothelial dystrophy (FED), and after penetrating keratoplasty (PK).…”

mentioning

confidence: 99%

The effect of corneal thickness on intraocular pressure measurement in patients with corneal pathology

Browning

Bhan²,

Rotchford³

et al. 2004

Background/aim: To compare intraocular pressure (IOP) measurements taken by the Goldmann applanation tonometer, the Tono-Pen and the ocular blood flow pneumotonometer in eyes with varying central corneal thickness (CCT) due to penetrating keratoplasty (PK), keratoconus (KC), and Fuchs' endothelial dystrophy (FED). Methods: IOP was measured with the Goldmann applanation tonometer, Tono-Pen XL, and OBF pneumotonometer in 127 eyes with the following corneal abnormalities. There were 56 eyes that had undergone PK, 37 eyes with KC, and 34 eyes with FED. CCT was measured using an ultrasound pachymeter after IOP determinations had been made. Results: Mean IOP measurements in all three patient groups were significantly higher when measured by OBF pneumotonometer. Linear regression analysis showed that patients with FED had a significant increase in IOP with increasing CCT of 0.18 mm Hg/10 mm using the Goldmann tonometer, 0.15 mm Hg/10 mm with the Tono-Pen, and 0.26 mm Hg/ 10 mm with the OBF pneumotonometer. In patients with KC and after PK, linear regression analysis did not show a significant effect of CCT on IOP. A multivariate linear regression model controlling for age, sex, graft size, and patient group, showed that the effect of CCT on IOP for Tono-Pen (0.13 mm Hg/10 mm CCT) and Goldmann (0.14 mm Hg/10 mm CCT) were significantly lower than for the OBF pneumotonometer (0.26 mm Hg/10 mm CCT). Conclusions: This study found that mean IOP measurements using the OBF pneumotonometer were significantly higher than those made using the Goldmann applanation tonometer or Tono-Pen in eyes with a variety of cornel pathologies. The OBF pneumotonometer was found to be most affected by variation in CCT. For all three instruments, the relation between IOP and CCT depended on the corneal pathology and was greatest for FED.