Hypercapnia and Retrobulbar Blood Flow Velocities in Normal Tension Glaucoma and Healthy Controls

Abstract

Abstract: : Purpose: To evaluate vasoreactivity of retrobulbar vessels provoked with hypercapnia. In normal tension glaucoma (NTG) an impaired vasodilatory response upon CO₂-provocation is postulated triggering a deficient capacity of blood flow regulation. Methods: Ten patients with NTG (57 ± 9 years) and ten age-matched healthy subjects (50 ± 11 years, p=0.13) were included in this prospective clinical study. Blood flow velocities (peak systolic velocity PSV, end-diastolic velocity EDV) and resistive indices (RI) of the ophthalmic artery and the central retinal artery were measured with color Doppler imaging (CDI). Blood flow velocities were measured under normocapnic and hypercapnic isooxemic conditions (increasing the end-tidal pCO₂ by 15%). Blood pressure, respiration rate and oxygen saturation were monitored simultaneously. Results: The PSV, EDV and the RI of the ophthalmic artery did not show any significant differences under normocapnic and hypercapnic conditions for NTG and controls. The PSV and EDV of the central retinal artery were significantly reduced during baseline examination in NTG (p<0.05). The PSV and EDV of the central retinal artery increased in hypercapnia significantly more pronounced in healthy controls than in NTG-patients (p<0.05, ANOVA). The RI of the central retinal artery remained unaffected in both groups. Blood pressure, respiration rate and oxygen saturation did not change significantly under hypercapnia. Conclusions: CO₂-provocation test reveals impaired vasoactive response of the central retinal artery in NTG. These changes could be in part as a result of abnormal autoregulation and metabolic state in eyes of NTG patients.

Keywords: clinical research methodology • imaging methods (CT, FA, ICG, MRI, OCT, RTA, S • optic flow