J Korean Ophthalmol Soc.  2015 Feb;56(2):228-233. 10.3341/jkos.2015.56.2.228.

Accuracy and Reliability of the Icare PRO in Enucleated Porcine Eyes - Upright and Horizontal Positions

• Lee KY
• Yoo YC

• KMID: 2216006
• DOI: http://doi.org/10.3341/jkos.2015.56.2.228

Abstract

PURPOSE
To compare the accuracy and reliability of intraocular pressure (IOP) measurements in enucleated porcine eyes using the Icare PRO in the upright and horizontal positions.
METHODS
We designed an enucleated porcine eye model whose anterior chamber was cannulated with a 30-gauge needle, connected in parallel to a pneumatic pressure device. The reference pressure was manipulated by changing the air pressure from 70 to 10 mm Hg at 10 mm Hg intervals, and the IOP of porcine eyes was measured with the Icare PRO at each pressure. Correlation analysis, comparison using the Bland-Altman plot and Wilcoxon signed rank test, was performed to assess the accuracy of IOP measurements. Intraclass correlation coefficients were calculated to assess the intra-observer variability in the upright and horizontal positions, respectively.
RESULTS
The IOP value in both upright and horizontal positions was well correlated with the reference pressure (r = 0.992 and 0.985, respectively). The Bland-Altman plot showed good agreement between the two positions. However, all IOP values in both positions were lower than the reference pressures. The IOP values in the horizontal position were significantly lower than those in the upright position at the a reference pressure of 50 mm Hg or greater. Values of intraclass correlation coefficient ranged from 0.911 to 0.984 when measured in the upright position and from 0.707 to 0.914 in the horizontal position.
CONCLUSIONS
IOP measurements of Icare PRO in porcine eyes were remarkably lower than reference pressures controlled by the pneumatic method even though they showed a good correlation with reference values. The higher was the reference pressure, the greater was the degree of underestimation of IOP measurement in both positions. This trend was more pronounced in the horizontal position, and the reliability of IOP measurements was also lower than that in the upright position.

Keyword

Accuracy; Horizontal position; Icare PRO rebound tonometer; Intraocular pressure; Reliability

MeSH Terms

Air Pressure
Anterior Chamber
Intraocular Pressure
Iron-Dextran Complex*
Needles
Observer Variation
Reference Values
Iron-Dextran Complex

Figure

• 

  Figure 1. Scatter plots showing the correlation between intraocular pressure with Icare PRO in the upright (IOPu) and horizontal (IOPh) position, respectively. They show reasonably good linear correlations between the measured IOP and reference pressure. Icare PRO measurements (Y-axis) are plotted against reference pressure (X-axis). Solid line indicates regression line whose formulae are y = 0.802 x -0.581 (A), y = 0.648 x +3.927 (B). (A) Upright positon, (B) horizontal position.

• 

  Figure 2. Bland-Altman plots including linear regression for all included eyes. X-axis: mean of reference pressure and IOP measurements performed in the upright position (IOPu) (A), IOP measurements performed in the horizontal position (IOPh) (B). Y-axis: difference between reference pressure with IOPu (A), IOPh (B). Solid line: bias (A: 8.5; B: 10.1). Dotted lines: 95% limits of agreement (A: -0.3 to 17.3; B: -4.5 to 24.8). Dashed line: slope (A: 0.21; B: 0.42 (p-value < 0.001)). IOP = intraocular pressure.

Reference

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