Reduced vascular response in patients with normal tension glaucoma in response to hypoxia

Abstract

PurposeIncreased evidence exists on an association between normal tension glaucoma (NTG) and endothelial dysfunction. Moreover, it is recognized that glaucomatous damage is linked to episodes with hypoxia. The aim of our study was to investigate the vascular response after hypoxia in patients with NTG compared to controls.MethodsThe vascular response was evaluated after hypoxia by Peripheral Arterial Tonometry (PAT) and recorded as Reactive Hyperemic Index (RHI). All subjects went through two days of investigation. In random order the first visit included either hypoxia or normoxia with successive measurements. Hypoxia/normoxia was induced in 2 h through a tightly fitting face mask. Additionally, the peripheral circulation was measured by a thermographic camera. Blood samples were taken before, during and after hypoxia/normoxia to evaluate stress factors such as cathecolamines. The two days of investigation were at least three weeks apart.ResultsRHI measurements showed a tendency of greater difference between hypoxia and normoxia in the NTG group. Thermographic images showed a tendency of colder temperatures in the fingertips of the NTG patients before hypoxia compared to the controls. A significant difference in temperature between the hypoxia day and the normoxia day was seen in the NTG group after both 2 h of hypoxia/normoxia and half an hour after the mask was removed. Adrenalin levels differed significantly in response to hypoxia in the control group, whereas no significant change was observed in response to hypoxia in patients with NTG.ConclusionsOver all, the vascular response to hypoxia was less prominent in patients with NTG compared to controls. This confirms a decreased ability to regulate the vascular tonus in response to vascular stress (hypoxia) in patients with NTG.