Comparing 24-hour IOP fluctuation slope curve between newly diagnosed ocular hypertension and primary open-angle glaucoma

Abstract

Objective: To compare the 24-hour intraocular pressure (IOP) fluctuation slope curve between newly diagnosed patients with ocular hypertension (OHT) and primary open-angle glaucoma (POAG).

Methods and analysis: Newly diagnosed and untreated OHT and POAG patients who underwent 24-hour IOP monitoring were consecutively enrolled in the study. IOP measurements were taken every 2 hours from 8:00 to 6:00 hours the following day using an iCare PRO tonometer. Patients maintained their daily routines, with IOP measured in a seated position during the day and supine at night. The 24-hour IOP fluctuation indices, including peak, trough and overall fluctuation, were calculated. Differences in the 24-hour IOP fluctuation slope curves over time between groups were analysed using a generalised additive mixed model.

Results: 46 patients with OHT and 41 with POAG were included. From 2:00 to 10:00 hours, mean IOP increased by 0.69 mm Hg every 2 hours in the POAG group (p<0.0001) and by 0.40 mm Hg in the OHT group (p<0.0001). After 10:00, the IOP showed a downward trend, decreasing by 0.31 mm Hg in the POAG group (p<0.0001) and by 0.17 mm Hg in the OHT group (p=0.0003) every 2 hours. The rate of slope change in the upward phase differed significantly between the groups (0.30 mm Hg per 2 hours; p=0.02), as did the rate in the downward phase (0.14 mm Hg per 2 hours; p for interaction=0.04). Multivariate models showed that each 1 mm Hg increase in circadian and diurnal IOP fluctuation was associated with a 27% and 21% higher likelihood of POAG presence, respectively.

Conclusion: The 24-hour IOP slope curve differed between POAG and OHT, with a steeper slope observed in the POAG group. However, the study is limited by potential confounding factors, reliance on a single 24-hour measurement period and the need for further longitudinal studies to validate these findings.

Keywords: Glaucoma; Intraocular pressure; Ocular Hypertension.

Figure 1. Participant selection and reasons for exclusion. CCT, central corneal thickness; IOP, intraocular pressure; NTG, normal-tension glaucoma; OHT, ocular hypertension; POAG, primary open-angle glaucoma; VCDR, vertical cup/disc ratio; VF, visual field.

Figure 2. Relationship between the time-varying pattern (TVP) in 24-hour IOP and clinical grouping (OHT vs POAG) in the generalised additive mixed model. The TVP in 24-hour IOP in the OHT and POAG groups followed an inverted ‘U’ curve with the trough IOP at 2:00 hours (set as the baseline for analysis). From 2:00 hours (trough) onward, the IOP increase showed an upward pattern. It reached an increasing peak at 10:00 and 12:00 hours, reaching close to the plateau period and then showed a downward pattern after 12:00 hours. The slope of the IOP curve in the POAG group (red) was steeper than that in the OHT group (blue). IOP, intraocular pressure; OHT, ocular hypertension; POAG, primary open-angle glaucoma.