Evaluation of the Effect of Hypercapnia on Vascular Function in Normal Tension Glaucoma

Introduction. Altered ocular perfusion and vascular dysregulation have been reported in glaucoma. The aim of this paper was to evaluate the vascular response to a hypercapnic stimulus. Methods. Twenty normal tension glaucoma (NTG) patients and eighteen age- and gender-matched controls had pulsatile ocular blood flow (POBF) measurements, systemic cardiovascular assessment, and laser Doppler digital blood flow (DBF) assessed. Measurements were taken at baseline, after 10-minutes rest, in the stable sitting and supine positions and following induction and stabilization of hypercapnia, which induced a 15% increase in end-tidal pCO(2). The POBF response to hypercapnia was divided into high (>20%) and low responders (<20%). Results. 65% of NTG patients had a greater than 41% increase in POBF following CO(2) rebreathing (high responders). These high responders had a lower baseline POBF, lower baseline DBF, and a greater DBF response to thermal stimulus. Conclusion. NTG patients that have a greater than 20% increase in POBF after a hypercapnic stimulus have lower baseline POBF and DBF values. This suggests that there is impaired regulation of blood flow in a significant subgroup of NTG patients. This observation may reflect a generalised dysfunction of the vascular endothelium.