Self-tonometry consistently measures diurnal IOP fluctuations
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Self-tonometry consistently evaluated diurnal IOP fluctuations in patients with ocular hypertension or open-angle glaucoma, according to a crossover clinical treatment trial in Optometry and Vision Science.
“Traditionally, 24-hour IOP profiling involves performing applanation tonometry measurements regularly over a 24-hour period, which is resource intensive and largely infeasible to implement in standard clinical practice,” Janelle Tong, BOptom, BSci, of the Centre for Eye Health and the school of optometry and vision science at University of New South Wales, Australia, and colleagues wrote. “Its inconvenience has spurred the development of technologies enabling IOP monitoring outside of office hours, including contact lens sensor-based devices such as the Triggerfish (Sensimed) and self-tonometry devices such as the iCare Home rebound tonometer (iCare Finland Oy).”
Tong and colleagues recruited 14 patients (10 men) with open-angle glaucoma or ocular hypertension who were using latanoprost 0.005% ophthalmic solution for at least 6 weeks.
After training on the iCare Home tonometer, participants performed self-tonometry on both eyes when they woke up, at lunch time, at dinner time and before sleep. During the self-tonometry period, participants continued latanoprost use for 1 week, ceased use for 4 weeks and then used timolol 0.25% gel-forming solution for 2 weeks.
IOP responses varied for latanoprost and timolol, with significant reductions for all IOP parameters with both medications in three subjects, significant reductions for some IOP parameters with one or both medications in nine subjects and no significant change in IOP parameters with either medication in two subjects.
“Meanwhile, the proportion of participants reaching a clinical target of at least 30% reduction in IOP fluctuations on either latanoprost or timolol was significantly greater than peak and mean IOPs, where the majority of patients demonstrating significant reductions achieved only a 10% to 30% reduction,” the study authors wrote. Among participants who had at least a 30% reduction in fluctuation, there was no significant difference in the percentage reductions in IOP fluctuation between the two drugs.
Longer duration of latanoprost use was associated with smaller reductions in peak and mean IOP on timolol (P = .007 for both). There were no significant associations between years of latanoprost use and IOP parameters during latanoprost use or between age and IOP parameters during either medication period.
Women had more significant reductions in IOP fluctuation than men with latanoprost (mean differences, 4.34 vs. 1.41 mm Hg; P < .02) and borderline significant reductions with timolol (mean differences, 2.83 mm Hg vs. 0.60 mm Hg). Sex was not associated with any other IOP parameters.
Limitations of the study included small sample size, a small number of women, few subjects with ocular hypertension, self-reported compliance and unmasked medication use.
“Further studies with a larger cohort on long-term latanoprost use and longer period of washout would be beneficial to confirm whether the findings are replicable and therefore whether further investigations regarding mechanisms affecting long-term IOP variations are warranted,” Tong and colleagues wrote.
Perspective
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Considering that IOP lowering is our sole glaucoma treatment, it behooves us to better understand how therapeutic interventions affect IOP. Studies have shown that in-office IOP testing may miss important information such as peak IOP and short-term diurnal IOP fluctuations. Tong and colleagues explore how home monitoring with the iCare home tonometer might shed some light.
While interesting, this small study (14 participants) did little to pique my interest in utilizing self-tonometry. Several factors have me doubting the validity of their findings. For example, they found considerable variability between subjects in response to treatment and found no difference between latanoprost and 0.25% timolol in achieving a 30% reduction in IOP fluctuations. This doesn’t ring true with my clinical experience, and they didn’t provide in-office data that might have supported these and other curious findings.
While true that our “snapshot” looks at IOP in office may be missing important information, I’m doubtful that adding a couple more snapshots with an at-home device will yield useful information. Glaucoma typically progresses slowly, and our effective treatments are empirically determined. With early detection, that data we lack may be of little significance, and this study suggests iCare at home tonometry will not add useful information.
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