Background

The Diaton Tonometer estimates intraocular pressure by rebound tonometry through the upper eyelid. A metal rod is released within the instrument and rebounds off the eyelid, superior tarsus, and superior sclera. The deceleration of the metal rod is used to estimate intraocular pressure. Obviously, in the vast majority of clinical scenarios, this strategy is inferior to methods of corneal applanation tonometry such as Goldmann applanation or the Tono-Pen.

However, in patients with a Boston Type I Keratoprosthesis (or KPro), accurate corneal applanation is impossible because of the rigidity of the central optic and peripheral backplate that surround the corneal graft.  In these patients, the current gold standard for estimating intraocular pressure is palpation of the sclera through the eyelid with the examiner’s finger. Because of the subjectivity of this technique, and the high rate of glaucoma in KPro patients, we have used the Diaton tonometer as an objective, though unproven, supplement to our estimates of intraocular pressure by finger palpation.

The evidence for the accuracy of the Diaton in normal patients is fair at best (Li 2010, Doherty 2012, Toker 2008). According to our preliminary unpublished research in patients with ocular hypertension, glaucoma, and glaucoma drainage devices, the Diaton is modestly reliable as a screening tool for elevated intraocular pressure.

In KPro patients, the accuracy of the Diaton has not been proven, and doing so would be challenging given the status of the current gold standard. However, there is presently no practical objective alternative to finger palpation in these patients, so use of the Diaton seems reasonable given the high incidence of glaucoma in these patients (Greiner 2011, Talajic 2012).

In our experience, the plausibility and reproducibility of Diaton measurements are largely dependent on patient positioning and user technique. First-time users who do not read the instruction manual or practice the technique will likely obtain questionable results and become suspicious of the Diaton’s reliability. Therefore, we created this video to demonstrate proper technique for the use of the Diaton and the common pitfalls we have encountered in our early experience using the device.

Disclaimer: EyeRounds.org and its authors have no financial interest in this device. For official device instructions and further details, please visit the manufacturer’s website at www.diaton-tonometer.com.

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