COMMENTARY

Self-tonometry: Good Potential but Not Yet Practical

Brianne N. Hobbs, OD

Disclosures

March 23, 2018

Real Potential for Self-tonometry?

Glaucoma is often a disease of subtleties. A tiny notch of rim tissue, an extra point of visual field depression, or even a single 1-mm Hg change in intraocular pressure (IOP) can alter the management of glaucoma. Challenging diagnostic and treatment decisions are sometimes made with only a few data points. If more data could be collected, individual trends in IOP such as time of peak IOP and variation in IOP theoretically could be identified, resulting in more effective management of glaucoma.

The theory of serial tonometry measurements is not new, but the methodology is. With the advent of home self-tonometry through the Icare® HOME tonometer (Icare USA; Raleigh, North Carolina), a multitude of data points can be collected, potentially allowing for a more accurate description of short- and long-term IOP fluctuations. The response to treatment can also be detected in a more expedient manner.

A recent study explored the potential implications of self-tonometry.

Study Summary

This study[1] investigated self-tonometry trends in 27 patients—nine with glaucoma and 18 glaucoma suspects. Glaucoma patients were newly diagnosed and had not been previously treated with any glaucoma medication. Enrolled patients initially engaged in a 30-minute training session and were required to demonstrate competence with the instrument prior to entering the data collection phase. Patients were instructed to measure their IOP four times a day in a seated position for 4-6 weeks. Data were downloaded directly from the instrument at the conclusion of the study. Patient satisfaction with the instrument and ease of use were assessed by a survey.

The two most common patterns of IOP fluctuation were peak IOP upon awakening and peak IOP at midday. In the glaucoma patients, initial response to treatment with latanoprost 0.005% ophthalmic solution was dramatic; average IOP reduced from 23.9 mm Hg to 16.1 mm Hg within the first 24 hours. Average compliance was 76% and was significantly higher in those with glaucoma compared with glaucoma suspects (84% vs 72%, respectively).

Viewpoint

The ability to more fully understand IOP fluctuations relative to glaucoma is a welcome advance, as it removes the constraints and limitations of IOP measurement in the office. For this technology to affect clinical care, however, self-tonometry has to be as accurate as Goldmann tonometry; at this time, that doesn't seem to be the case.

The Icare HOME tonometer overestimated the average baseline IOP (25.5 mm Hg) compared with applanation tonometry (22.9 mm Hg) in glaucoma patients. The percent change in IOP with treatment also varied significantly between self-tonometry and applanation tonometry—an important discrepancy. These findings are consistent with previous studies[2] that found that self-tonometry tends to overestimate higher IOPs and underestimate lower IOPs.

A major problem with the Icare HOME tonometer was the ease of use, or lack thereof. Originally this study included 40 patients, but only 67.5% of recruited patients were able to use the device as required—20% were unable to pass the competency test, three patients didn't collect enough data, and two patients withdrew. Most patients rated the instrument as "easy to use" overall, but a number of patients reported difficulty correctly positioning the instrument on the eye. Testing the left eye was also reported by a few patients to be more difficult than the right eye. Advances in the design of this self-tonometer are needed to increase utility.

The ongoing development of self-tonometry should be followed; but, at this time, it is likely practical for only a small percentage of those with glaucoma and glaucoma suspects.

In the future, self-tonometry could assist with appointment scheduling (by scheduling IOP checks at their peak times), more accurate diagnosis of glaucoma, and more effective management of glaucoma by prompt analysis of the treatment effect.

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