Abstract
Purpose: :
To study blood pressure (BP), intraocular pressure (IOP), and day and nighttime ocular perfusion pressure (OPP) parameters in patients with untreated normal tension glaucoma (NTG) in the habitual position, and to investigate the relationship between day and nighttime OPP parameters and glaucomatous damage at initial presentation.
Methods: :
IOP and BP were evaluated in the habitual position during 24-hour hospital monitoring in patients with NTG. Patients were classified into three groups: non-dippers; dippers; and over-dippers, corresponding to the degree of reduction in their nocturnal mean arterial pressure (MAP) compared with diurnal MAP. OPP was calculated for diurnal, nocturnal, and circadian period from the 24-hour IOP and BP data. Multivariate regression models were used to evaluate potential risk factors for glaucomatous damage: age; central corneal thickness (CCT); myopia; mean/peak in-hospital IOP; average day, night, and 24-hour mean arterial pressure (MAP), and average day, night, and 24-hour mean OPP. Functional outcome variables for glaucomatous damage were mean deviation (MD), and pattern standard deviation (PSD). Anatomic outcome variables were TSNIT (temporal, superior, nasal, inferior, and temporal) average, superior average, inferior average, and nerve fiber indicator (NFI) on Scanning Laser Polarimetry (GDx VCC).
Results: :
Among 90 NTG patients, twenty four (26.7%) patients were classified into the non-dipper group, 20 (22.2%) into the dipper group, and 46 (51.1%) into the over-dipper group. Marked nocturnal mean OPP fluctuation was noted in the over-dipper group (p < 0.05). In the multivariate regression models, lower nocturnal mean OPP was significantly associated with decreased average TSNIT and increased likelihood of glaucoma (NFI score) among outcome variables. Lower nocturnal mean OPP trough value was associated with decreased average TSNIT and increased NFI score. Age was also a strong predictor of glaucomatous damage.
Conclusions: :
Large nocturnal mean OPP fluctuation was associated with nocturnal BP drop. Marked nocturnal OPP reduction was the most consistent clinical risk factor for glaucoma severity in eyes with NTG when estimated in the habitual position. These findings may suggest an etiology of NTG as a chronic and ischemic end organ disease.
Keywords: intraocular pressure • optic nerve • visual fields