iCare HOME2 Monitoring of Diurnal Ocular Perfusion Pressure in Patients With Nonarteritic Ischemic Optic Neuropathy

This study evaluated time-of-day differences in intraocular pressure (IOP), mean arterial pressure (MAP), and ocular perfusion pressure (OPP) in eyes affected by nonarteritic anterior ischemic optic neuropathy (NAION), and compared these measures between NAION-affected and unaffected eyes at each time period.

Adults aged 18-90 years with a confirmed diagnosis of NAION were enrolled in this nonrandomized prospective observational cohort study. Participants were trained to measure blood pressure (BP) and IOP using an automated BP cuff and the iCare HOME2 rebound tonometer. In participants with only 1 eye affected by NAION, the unaffected eye was used as a control. Measurements were collected at 7 predefined daily time points (4:00, 6:00, 9:00, 12:00, 15:00, 18:00, and 21:00) for at least 7 consecutive days. MAP and OPP were calculated as 1/3 systolic + 2/3 diastolic pressure and 2/3 × (MAP - IOP), respectively. Early morning (4:00, 6:00), midday (9:00, 12:00, 15:00), and evening (18:00, 21:00) measurements were compared using linear mixed-effects models. The main outcome measures were intraday measurements of IOP, MAP, and OPP.

A total of 27 eyes of 15 patients were included in the study. Among NAION-affected eyes, mean OPP and MAP were lowest in the early morning. No IOP elevations were noted in the early waking hours. On average, OPP was 1.69 mm Hg higher and MAP was 2.70 mm Hg higher at midday than in the morning, while IOP increased by 0.76 mm Hg (all 95% confidence interval [CI]). In the evening, OPP was 1.83 mm Hg higher and MAP was 2.49 mm Hg higher than in the morning (both 95% CI). Evening IOP was 0.31 mm Hg lower than in the morning, but this difference was not statistically significant ( P = 0.08).

Early morning low OPP in nonglaucomatous eyes with NAION seems to be correlated with low MAP, rather than elevated IOP. These findings help support a role for impaired local perfusion in the early waking hours in the pathogenesis of NAION and highlight the potential utility of IOP and BP diurnal monitoring in at-risk patients.