Publisher: St. Erik's Eye Hospital, Sweden

Authors: Quérat, Laurence

Self-monitoring of intraocular pressure and its clinical application


Purpose: Measuring the intraocular pressure (IOP) is one of the most common ophthalmologic examinations, especially within glaucoma management. An elevated IOP is a major risk factor for the development and progression of glaucoma, and is so far the only modifiable parameter. Treatment consists of lowering the IOP to slow down the disease, and the effect of treatment is evaluated by monitoring the IOP level and visual field status. Until recently, IOP measurements were performed by healthcare personnel at the eye clinic or by optometrists and opticians. A decade ago, a new tonometer was launched on the market, aimed at allowing patients to measure their own IOP. The purpose of this thesis was to evaluate the feasibility of self-tonometry by glaucoma patients and healthy volunteers, and the reliability of their measurements compared with the gold-standard method, Goldmann applanation tonometry (GAT). We also wanted to observe IOP variations and IOP patterns over consecutive days. Furthermore, we wanted to investigate the inter-user variability with both methods. Finally, we wanted to examine the impact of self-tonometry on clinicians’ decision-making regarding glaucoma treatment.

Methods: In the research reported in Papers I, II, and III, glaucoma patients and healthy volunteers were trained to use a self-tonometer at the eye clinic. Measurements from the participants and trainers were recorded at the eye clinic. In Papers I and II, participants borrowed the self-tonometer over a few days to collect additional IOP measurements. In Paper III, additional measurements made by healthcare personnel at the clinic were collected as well. IOP values obtained by different users and different methods were analyzed, as well as IOP levels over consecutives days. In Paper IV, medical records from glaucoma patients who had performed self-tonometry were retrospectively reviewed. Different parameters were analyzed to evaluate which parameters had the most impact on the clinicians’ decisions.

Results: We found that more than 85% of the participants were able to perform self-tonometry (Paper I, II, and III). Overall, approximately 70% of the measurements made with iCare self-tonometers were within 3 mmHg of GAT measurements. IOP means were similar between the different users and methods. In Papers I and II, more than 60% of glaucoma patients had their highest IOP level in the morning. Between 9%–16% of glaucoma patients and healthy volunteers had an IOP peak outside office hours. There was good agreement between the methods of self-tonometry and GAT, although Bland-Altman analyses showed a bias with a cut-off at 18–20 mmHg in Paper I and 15 mmHg in Papers II and III. There was good repeatability of measurements, although we found a statistically significant difference in Paper III between the trainers’ values obtained with GAT and those obtained with a self-tonometer, as well as between the trainers’ and other healthcare personnel’s values obtained with GAT. The reliability between the users was excellent with iCare Home, at 0.903 (95% CI 0.880–0.959) and good with GAT, at 0.741 (95% CI 0.558–0.849). In Paper IV, we found a statistically significant difference between the clinicians’ decision to keep the existing treatment or escalate therapy based on maximum and mean IOP.

Conclusions: Our studies showed that self-tonometry was feasible and that the measurements made by participants were reliable. Different IOP patterns from day to day and the presence of IOP peaks outside office hours support the idea of monitoring IOP over several days. We showed that tonometry with iCare Home used by the patients themselves had similar or less inter-user variation compared with GAT measured by healthcare professionals. Finally, we found that high IOP measurements collected during IOP phasing with self-tonometry could motivate additional treatment. Self-tonometry appeared to be a useful method to confirm that the present treatment was probably adequate when no deviating IOP values were observed. Thus, self-tonometry provided clinicians with a solid basis on which to make their decisions and avoid a possible under- or over-treatment for the benefit of patients. Self-tonometry with iCare Home appears to be a valuable complement to traditional glaucoma care