Purpose To evaluate long-term intraocular temperature (IOT) variations in eyes with primary open-angle glaucoma (POAG) using an intraocular telemetric sensor.

Methods This prospective, open-label, multicentre observational study analysed the IOT variations in 22 eyes of 22 patients with POAG. All enrolled patients underwent implantation of an intraocular pressure (IOP) sensor during cataract surgery. The telemetric system uses a built-in temperature sensor to control measured IOP for temperature. Each time a patient measures their IOP, both the IOP and IOT are recorded in the reader device. Patients were instructed to self-measure their IOP as often as desired, but at least four times daily. Recorded readings were retrieved and analysed using mixed effect models and pairwise comparisons using Bonferroni correction to assess the statistical significance of average IOT variations between each individual weekday and calendar month.

Results The mean age of patients was 67.8±6.8 years and 36.4% were women. A total of 132 745 readings over 21 102 measurement-days were obtained. On average, IOT was significantly higher on Sundays (34.57°C; 95% CI 34.37 to 34.78) than on any other day of the week (p<0.001). Mean IOT on other weekdays ranged from 34.48°C to 34.51°C. Over the year, IOT followed a clear seasonal pattern, reaching its maximum in July (34.8°C; 95% CI 34.56 to 34.97) and its minimum in January (34.4°C; 95% CI 34.15 to 34.56; p<0.001).

Conclusions This study demonstrates the feasibility of continual and long-term measurement of IOT using intraocular sensors. The results show significant short-term and long-term fluctuations of IOT. Research is warranted to understand the impact of IOT variations on IOP, ocular perfusion and glaucoma progression.