Effect of levodopa on contrast sensitivity and scotomas in human amblyopia

The neurotransmitter dopamine (DA) is involved in several visual functions. Visual deprivation decreases retinal DA concentration in chickens and monkeys. In animals with deprivation amblyopia, several studies suggest that neurotransmitters are involved in visual-cortical plasticity and can restore partial visual acuity in adult cats. We investigated in a cross-over, double-masked study the influence of levodopa on contrast sensitivity and binocular suppression in human adult strabismic and amblyopic patients. After one single administration of levodopa, a significant increase in contrast sensitivity and decrease of the size of the fixation point scotoma was found. No changes could be detected after placebo administration. Levodopa did not induce changes in contrast sensitivity in the dominant eyes of the patients or in normal subjects. In conclusion, we found a short-term effect of levodopa on contrast sensitivity and fixation point scotomas in amblyopic eyes of adult patients.