Short‐term intraocular pressure fluctuation in primary angle closure glaucoma

Purpose: To identify the most sensitive period for detecting significant circadian and ultra‐short‐term intraocular pressure (IOP) fluctuation associated with disease progression in primary angle closure glaucoma (PACG). Methods: PACG eyes, which had been followed up for over 2 years under the CUHK PACG Longitudinal (CUPAL) Study, were recruited. Eyes with or without functional or structural glaucomatous progression were classified into ‘progressive’ or ‘stable’ groups based on serial visual field (VF) and retinal nerve fibre layer (RNFL) thickness documentations, respectively. Circadian and ultra‐short‐term IOP fluctuations were recorded by Sensimed Triggerfish® sensors with 288 readings over 30 s, at 5‐min intervals, over a 24‐h period. The circadian IOP fluctuation was represented by smoothed sensor output signals using B‐spline smoothing transform and described by functional data analysis. In each of seven activity‐related 1‐h periods during the examining day, the mean value of the amplitude‐frequency profiles of the signal fluctuations in twelve 30‐s intervals, which represent the ultra‐short‐term IOP fluctuation, was calculated by semi‐variogram/semi‐variance. The signals were compared between ‘progressive’ and ‘stable’ groups by permutation tests on functional t‐statistics. Results: Among the 25 recruited PACG eyes, 16 eyes were classified as RNFL ‘progressive’ group (the mean rate of change in global RNFL thickness: −0.199 ± 0.128 μm/month). Statistically significant differences were found during the time periods from 22:00 to 23:00 and from 07: 00 to 08:00 in gradients that reflected by the first derivative of the IOP fluctuation curve, as well as from 23:00 to 24:00 and 08:00 to 09:00 in curvatures that reflected by the second derivative of the IOP fluctuation curve, between the VF progressive and the VF stable groups (p