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Editors Selection IGR 18-2

Clinical Examination Methods: IOP Temperature Measurements

Comment by Luciano Quaranta on:

100359 Measurement of intraocular temperature in glaucoma: week-day and seasonal fluctuations, Mansouri K; Gillmann K; Rao HL et al., British Journal of Ophthalmology, 2023; 107: 941-945

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This paper reports results on the evaluation of both the short-term and long-term variability of intraocular temperature (IOT) patterns in eyes with primary open-angle glaucoma (POAG) based on measurements collected with an intraocular pressure sensor the second generation eyemate-IO system (Implan-data Ophthalmic Products GmbH, Hannover, Germany) implanted in 22 patients during cataract surgery. The implant is powered externally by an electromagnetic field produced by the hand-held reader (Mesograph), which also acts as an antenna for the transmission of the reading signals emitted by the sensor. The mesograph also contains an ambient temperature sensor.

To obtain a measurement, the reader and the sensor implant need to be brought in close proximity with each other to activate the electromagnetic coupling sequence. During the sequence, ten measurements per second are made and averaged. The resulting IOP is recorded on the reader unit. Temperatures measured by the sensor and the mesograph on each occasion IOP measurement are also recorded.

The data collecting device was the abovementioned implanted sensor along with an external reading device able to provide power supply to the sensor via electromagnetic coupling as well as to perform as a data relay both via a cable connection or wireless into a web-based database.^1,2 Patients were trained on how to measure their own IOP with the device and were instructed to carry out at least four measurement cycles per day. The 24-hour day duration was split into seven time periods, in which measurement cycles could take place. Twenty-two eyes of 22 patients underwent cataract surgery with implantation of the eyemate-IO sensor. Their mean age was 67.8 ± 6.8 years, and eight (36.4%) were women. A total of 132745 readings over 21102 measurement days were obtained from the sensor during the study period. The average number of measurements obtained from each study eye was 6.3 per day.

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).

In my opinion, three aspects must be analyzed.

Firstly, as the authors correctly state in the paper, at present we do not have any normative data on IOT, to make a comparison with glaucoma patients. This is an important aspect to be further clarified in order also to understand if IOT has a potential role in glaucoma onset and progression (differences between normal and glaucoma patients).

Secondly, short-term IOT patterns. This finding is really intriguing. As a matter of fact, IOT increase during the night-time could be correlated with the decrease of aqueous humor production during sleep. In this prospect, if IOT increase should be considered a risk factor for glaucoma progression, further decrease of aqueous humor production during the night should be avoided or limited.

Thirdly, clinical meaning of IOT and its variations. The clinical meaning of increase of IOT in not completely understood. At the present only speculations can be drawn on the role of this variable on retinal ganglion cells vulnerability/apoptosis. Further pre-clinical and clinical investigations are warranted to understand the impact of IOT variations on glaucoma progression.

Overall, this is an outstanding job, based on an innovative and promising approach. Studies must go on, especially with regards to long-term variability for which the authors of this paper themselves claim there is a strong data paucity bias. Studies on short-term variability should consider and include different timeframes for both data collection and interpretation. The hours of the day should be covered more uniformly. These findings can have important implications both for clinical glaucoma management and clinical trials. We congratulate Kaweh Mansouri and coworkers for their so valuable contribution.

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