AIM: To evaluate the accuracy of the single measurement of intraocular pressure in 24h and to explore the differences of intraocular pressure in different body positions at night.

METHODS: A prospective study. A handheld tonometer(iCare-PRO rebound tonometer)was used to measure the intraocular pressure for 24h with 24 patients(48 eyes)who were measured for 48h at 7:00, 10:00, 14:00, 18:00, 22:00, 02:00, 05:00 from July to August in 2019 in the department of Ophthalmology, Jiaxing Hospital of Traditional Chinese Medicine, Intraocular pressure measurements in sitting and lying positions were performed at 22:00, 2:00, and 5:00. Intraocular pressure measurements in lying positions were measured at first. Then the patients were required to remain the sitting position for 10min, and measured the intraocular pressure in sitting positions again. Repeated measurements were used in the intraclass correlation coefficient(ICC)within-group to analyze consistency. The intraocular pressure of different body positions at night was analyzed and compared with the paired t test.

RESULTS: The ICC value at each time point fluctuates between 0.79-0.94, most of which are around 0.90 and both eyes are basically the same. The ICC values in the night time decubitus position fluctuated from 0.73 - 0.91, mostly above 0.86. The ICC value at each time point was above 0.75, most of which was around 0.90 which shows the consistency of repeated intraocular pressure measurements at each time point is good. However, the ICC results of intraocular pressure fluctuations were poor. The ICC value of the right eye was 0.49 and the left eye was 0.55. The ICC value of the right eye in lying positions was 0.40 and the left eye was 0.43. The consistency of the right eye was poor. The intraocular pressures in lying positions at night were higher than that in the sitting position, which was a difference at all time points.

CONCLUSION: A single 24h intraocular pressure measurement may not be highly reproducible, especially for intraocular pressure fluctuations. The reliability of the results of one measurement needs to be studied. The intraocular pressure measurement in the sitting position at night may not represent the actual intraocular pressure during sleep at night.