Purpose: To assess novel differences in serum levels of glucose, lactate and amino acids in patients with normal-tension glaucoma (NTG) compared to agematched controls, at baseline and in response to universal hypoxia. Methods: Twelve patients diagnosed with NTG and eleven control subjects underwent normobaric hypoxia for 2 hr. Peripheral venous blood samples were taken at baseline, during hypoxia and in the recovery phase. Serum glucose and lactate levels were measured by a blood gas analyser. Amino acids were analysed by high-performance liquid chromatography. Results: Baseline levels of lactate and total amino acids were significantly lower in patients with NTG compared to healthy controls. No differences were seen in blood glucose levels between the two groups. Lactate levels remained unchanged during hypoxia in the control group, but increased in patients with NTG. In the recovery phase, total amino acid levels were reduced in the control group, whereas no changes were found in patients with NTG. Conclusion: Reduced serum levels of lactate and total amino acids were identified as potential markers for NTG. Moreover, significant differential regulatory patterns of certain amino acids were found in patients with NTG compared to control subjects. Overall, our results suggest a link between systemic energy metabolites and NTG and support a novel understanding of glaucoma as an inner retinal manifestation of a systemic condition.

Purpose. To investigate whether patients with normal tension glaucoma (NTG) show an enhanced stress response to reduced oxygen supply compared to age-matched healthy controls, measured by serum adrenaline and endothelin-1 (ET-1) levels and changes in distal finger temperature. Methods. A thorough clinical characterization of patients with NTG and age-matched controls was performed prior to inclusion in the study. Twelve patients with NTG and eleven healthy controls met the inclusion criteria and were enrolled in the study. All subjects underwent a two-day investigation. Participants were randomly exposed to either hypoxia or normoxia during the first visit. Hypoxia or normoxia was induced for two hours through a tightly fitting face mask. In addition, the peripheral circulation was assessed with a thermographic camera. Blood samples were obtained before, during, and after hypoxia or normoxia to evaluate systemic stress molecules such as catecholamines and ET-1 levels. Results. In patients with NTG, reduced oxygen supply induced an increase in peripheral blood adrenaline ( p  < 0.05) and a decrease during recovery ( p  < 0.01). A difference in distal finger temperature was shown in patients with NTG under hypoxia compared to normoxia (exposure: p  < 0.05; recovery: p  < 0.05). Hypoxia induced an increase in peripheral blood ET-1 levels in both groups (NTG: p  < 0.01; controls: p  < 0.05). Conclusion. Patients with NTG had an enhanced physiological stress response as a consequence of hypoxia compared with age-matched controls. Although more studies are needed, the present study supports the involvement of vascular risk factors in the pathophysiology of NTG.

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.