Aims-To assess the effects of the nitric oxide donor 5-isosorbide mononitra
te (ISMO) on blood flow in the optic nerve head (ON flow) and choroid (Ch f
low).
Methods-Laser Doppler flowmetry was used to measure ON flow and Ch flow in
12 normal subjects by aiming the laser beam at the fovea and at the tempora
l rim, respectively. In a double masked, randomised, crossover design, each
subject received orally on separate days either 20 mg of 5-isosorbide mono
nitrate (ISMO) or placebo. Ch flow and ON flow were determined monocularly
at baseline and 1 hour after dosing. In the last six subjects, additional m
easurements were obtained at 3 hours. Mean arterial blood pressure (BPm), h
eart rate, and intraocular pressure (IOP) were monitored, and ocular perfus
ion pressure (PP) was estimated.
Results-No significant changes in ON flow, PP, IOP, or BPm were observed fo
llowing placebo. Following ISMO, ON flow increased from baseline by 19.8% (
SEM 9.3%) at 1 hour (paired t test, p = 0.058) and by 33.1% (7.5%) at 3 hou
rs (p = 0.007). Compared with the changes following placebo, statistically
significant increases in ON flow were observed both at 1 (p=0.050) and 3 ho
urs (p=0.041) after ISMO treatment. Compared with placebo, PF decreased sig
nificantly 1 hour after ISMO dosing (p=0.039), mainly as a function of redu
ced BPm. A significant inverse correlation (R=-0.618; p=0.032) was observed
between the percentage changes in PP and ON flow 1 hour following ISMO adm
inistration, but not after placebo. No significant change in foveal Ch flow
was documented.
Conclusions-These results suggest that, in normal subjects, ISMO increases
significantly ON flow but not Ch flow. The inverse correlation observed bet
ween PP and ON flow suggests that the same mechanism(s) responsible for sys
temic vasodilatation and blood pressure decrease may also cause the ON flow
increase.