Changes in Optic Nerve Head Circulation in Response to Vasoactive Agents: Intereye Comparison in Monkeys with Experimental Unilateral Glaucoma

PURPOSE: To investigate circulatory changes in the optic nerve head (ONH) in response to vasoactive agents including calcium antagonists, a substrate of nitric oxide (NO), and an inhibitor of NO synthase (NOS) in monkeys with unilateral experimental glaucoma. METHODS: Argon laser cautery to the trabecular meshwork was used to create experimental unilateral glaucoma in nine monkeys. The effects of systemic lomerizine or nilvadipine (calcium-antagonists), L-arginine (a substrate of NO), and NG-nitro-L-arginine methyl ester (L-NAME, a NOS inhibitor) on the ONH tissue blood velocity (NB(ONH)) was studied by the laser speckle method. RESULTS: Lomerizine and nilvadipine significantly increased NB(ONH) in the untreated normal eyes (P = 0.039 and 0.008, respectively), while significant, less increases were found in the laser-treated experimental glaucomatous eyes with significant intereye differences (P = 0.036 and 0.011, respectively). L-arginine significantly increased NB(ONH) in both eyes without intereye difference (P = 0.71). L-NAME had no significant effects on NB(ONH) in the experimental glaucoma eyes; however, it produced a significant decrease in the nonlaser treated eyes (P = 0.036). CONCLUSIONS: In experimental glaucomatous eyes, the reactivity of ONH vessels to calcium antagonists was preserved, but was significantly reduced. The response to a NOS inhibitor was lost; however, reactivity to a substrate of NO was normal. These data indicate that in experimental glaucoma, vasodilator reactivity in the peripheral vasculature of the ONH is preserved, but functional alterations are likely to affect reactivity to the NO system.