<h4>Purpose</h4>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.<h4>Methods</h4>A thorough clinical characterization of patients with NTG and age-matched controls was performed prior to inclusion in the study. This evidence concerns the gene EDN1 and low tension glaucoma.