What’s the Frequency?

At the present time, IOP remains the only clinically proven modifiable risk factor for glaucoma, and IOP measurements are vital for diagnosis and for judging the adequacy of therapy by reaching a target IOP. Daily diurnal IOP fluctuations are well-recognized – with particularly large ‘swings’ occurring in glaucomatous eyes. Although peak IOP has been definitively correlated with disease progression, and IOP fluctuation may be a separate risk factor for glaucoma, practicality has limited tonometry to a ‘split second’ in-office determination with patients in an upright position. Is this really an adequate sampling of IOP to drive clinical decisions?

An additional concern is the revelation that supine, nocturnal IOP is generally higher then upright, daytime IOP readings. Studies have also raised questions about activities that may lead to large IOP elevations, such as yoga, playing wind musical instruments, and sleeping on one side. There are also concerns about medical therapy inducing troughs and spikes in IOP as drug effects wane; consistent adherence with drug therapy; and the ineffectiveness of certain drugs at night. In other diseases, such as systemic hypertension and diabetes mellitus, there have been welcome advances in providing 24-hour measurements for advanced care, and it is great to see that those models have spurred a potential restructuring of glaucoma management.

Attempted methods to generate more IOP information have included performing in-office tonometry measurements at different times of the day and sleep laboratories dedicated to serial tonometry over 24 hours. But these options are of limited value since they are impractical for most,  preventing widespread adoption into clinical practice. Fortunately, there are emerging, innovative methods on the horizon that promise a larger sample of IOP measurements through home tonometry and telemedicine (1).

Patients can now be instructed on the home use of the iCare rebound tonometer without any need for corneal anesthesia. The majority of patients have been able to master the instrument and obtain meaningful measurements that are reasonably close to the gold standard Goldmann tonometry values. In one study, use of the Icare tonometer led to an adjustment in therapy in over 50 percent of patients (2). Another available tool is the Triggerfish contact lens, which has imbedded strain gauges that are able to detect relative changes in IOP (but not in mmHg). Studies using the contact lens verified peak IOP times during surveillance and documentation of a response to therapy. Both the iCare tonometer and Triggerfish contact lens have gained international approval by regulatory agencies. Implantable IOP sensors that are surgically placed in the eye have also been developed, and early clinical trials have been conducted (3). Thousands of IOP measurements are possible daily, and that information may be transmitted to a computer or smart phone; the specific IOP data and its presentation in a meaningful, useful manner will evolve.

There may be initial resistance raised about the amount of IOP data, the additional work needed to interpret that data, and questions raised about reimbursement. However, rapid assessment of response to therapy, nonadherence and extent of IOP fluctuations are reasonable expectations. Such information will undoubtedly enable clinicians to offer more rapid and timely adjustments in therapy. The promise of novel 24-hour IOP monitoring technology – whether home tonometry or IOP sensors – will revolutionize and optimize glaucoma care with a triple win: fewer office visits, more cost-effective care – and better outcomes for patients.