Ocular pulse amplitude (OPA) was measured to investigate the influence of peripheral vasoconstriction and vasodilation on choroidal perfusion in healthy volunteers and to determine whether low OPA in low-tension glaucoma (LTG) patients is associated with a vasospastic reaction and its response to the calcium channel blocker nifedipine.OPA was determined using the Langham ocular blood flow (OBF) system, applanation intraocular pressure (IOP), systemic blood pressure, and heart rate were measured, and ocular perfusion pressure was calculated before and after exercise and smoking in 12 otherwise nonsmoking, healthy volunteers and prior to and for 3 months after initiation of nifedipine therapy in 32 LTG patients with and without a vasospastic reaction as manifested by a nailfold capillary blood flow test.Exercise significantly (P 0.1) affected by changes in these parameters. Smoking significantly (P 0.09) alter OPA. There were two distinct LTG subtypes, with and without a vasospastic reaction. Only those with a vasospastic reaction showed a significant (P < 0.001) increase in OPA after 3 months of nifedipine treatment, while all other parameters tested were not significantly altered.Despite affecting ocular and systemic perfusion parameters, exercise and smoking did not alter OPA, suggesting functional isolation, i.e. autoregulation of the choroidal and/or ophthalmic artery circulation in healthy volunteers. Low OPA in LTG was increased by nifedipine only in vasospastic LTG patients, suggesting different, vasotonus-related pathologies. Calcium channel blockers and other vasodilators may be useful in vasoreactive LTG patients with reduced OPA.