Is the Icare Home tonometer affected by corneal biomechanical properties?
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Entering edit mode
3 months ago
@member

I know that FitEyes is currently recommending two tonometer options for self-monitoring of intraocular pressure at home. One is the Reichert 7CR, which has the advanced ability to compensate for corneal biomechanical properties. It gives a corrected IOP value called IOPcc.

Another recommended option is the Icare HOME tonometer. I know it is less expensive and it is portable. Does it have a similar capability to adjust IOP for corneal biomechanical properties?

tonometer corneal-biomechanics self-tonometry intraocular-pressure Icare • 110 views
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Entering edit mode
3 months ago
david 2.8k
@david_fe

Yes, those tonometers (the Icare HOME and the Reichert 7CR) are both good choices for self-tonometry. The Reichert provides research-quality IOP data even when used at home (and especially when combined with the free FitEyes software). But the Icare offers convenience, portability and lower cost, as you stated.

The Icare, like the vast majority of professional-grade tonometers used in medical practices today, does not measure or adjust for corneal biomechanical properties. Only a few tonometers do that.

As a community, we are very fortunate that we do have a tonometer option that offers that feature and is also suitable for home use. But that does not take away from the viability of the Icare HOME.

We are at an early stage of the self-tonometry revolution for glaucoma care. Most people living with glaucoma do not even have access to a home tonometer. Either of the tonometers we usually recommend are great -- and far better than not having a tonometer. However, FitEyes is always at the leading edge of tonometer technology, so you will see conversations about the few advanced tonometers that can measure and compensate for corneal biomechanical properties.

The Icare HOME is approximately as accurate as most professional tonometers used in medical practices today. Are there a few more accurate tonometers? Yes. Is the Reichert 7CR more accurate? Yes. Is the average Goldmann tonometer significantly more accurate than an Icare HOME? No. Most tonometers in use today, even those used in professional medical practices, do not measure and compensate for corneal biomechanical properties.

Here's a relevant paper directly addressing your question:

The Influence of Corneal Biomechanical Properties on Intraocular Pressure Measurements Using a Rebound Self-tonometer - PubMed

Abstract

Purpose: The purpose of this study was to examine the effect of corneal biomechanical properties on intraocular pressure (IOP) measurements obtained using a rebound self-tonometer (Icare HOME) compared with Goldmann applanation tonometry (GAT).

Methods: An observational study of 100 patients with glaucoma or ocular hypertension. All had a comprehensive ophthalmic examination and standard automated perimetry. IOP was assessed by GAT, Icare HOME and Ocular Response Analyzer, which was also used to assess corneal hysteresis (CH) and corneal resistance factor (CRF). Central corneal thickness (CCT) was recorded.

Results: Mean (±SD) IOP measurements were 14.3±3.9 and 11.7±4.7 mm Hg using GAT and Icare HOME, respectively. Average CCT, CRF, and CH were 534.5±37.3 μm, 9.0±1.7 mm Hg, and 9.4±1.5 mm Hg, respectively. The mean difference between Icare HOME and GAT was -2.66±3.13 mm Hg, with 95% limits of agreement of -8.80 to 3.48 mm Hg, however, there was evidence of proportional bias. There was negative correlation between IOP and CH [5.17 mm Hg higher Icare HOME IOP (P=0.041, R=0.029) and 7.23 mm Hg higher GAT IOP (P=0.008, R=0.080) for each 10 mm Hg lower CH], whereas thinner CCT was significantly associated with lower IOP (P<0.001, R=0.14 for Icare HOME and P<0.001, R=0.08 for GAT). In multivariable analysis, although CRF and CH remained associated with IOP measured using either GAT or Icare HOME, CCT was no longer significant.

Conclusion: IOP measurements obtained using a self-tonometer, similar to GAT, were more influenced by overall corneal biomechanics than CCT.

My commentary about the conclusion. That last statement is true for every tonometer. All tonometers are more influenced by overall corneal biomechanics than by CCT. A few advanced tonometers can make a correction based on corneal biomechanics. A patient's tonometer measurements should not be manually corrected for CCT, as discussed here.

The Icare uses a technology called "rebound tonometry."  Here's a link to another Icare study related to your question:

The effect of corneal biomechanical properties on rebound tonometer in patients with normal-tension glaucoma - PubMed

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