Relationship between the effect of carbon dioxide inhalation or nilvadipine on orbital blood flow in normal-tension glaucoma

Purpose: To investigate the relationship between the effect of carbon dioxi de (CO2) inhalation or oral nilvadipine, a calcium-channel blocker, on orbi tal blood flow in patients with normal-tension glaucoma, as determined by c olor Doppler imaging. Patients and Methods: Sixteen patients with normal-tension glaucoma (mean a ge, 55.6 +/- 9.8 years; male:female ratio, 3:13) underwent color Doppler im aging to measure the resistance index, and peak systolic and end-diastolic blood flow velocities of the ophthalmic artery, central retinal artery, and nasal and temporal short posterior ciliary arteries. Measurements were tak en before and during CO2 supplementation sufficient to increase the end-tid al CO2 partial pressure by 10%. The color Doppler imaging measurements were repeated after 2 to 4 weeks of treatment with 2 mg oral nilvadipine, and c omparisons were made between the effects of the two treatments. Results: Both CO2 inhalation and nilvadipine treatment significantly reduce d the resistance index in the central retinal artery, nasal short posterior ciliary artery, and temporal short posterior ciliary artery. There was a s ignificant correlation between the effects of the two treatments on the dif ference in the resistance indexes of the ophthalmic artery and central reti nal artery, but not on those of the nasal or temporal short posterior cilia ry artery. Conclusions: Both CO2 inhalation and oral nilvadipine significantly reduce the resistance index measured by color Doppler imaging in orbital vessels. The effect of oral nilvadipine might be predicted by CO2 inhalation in pati ents with normal-tension glaucoma.