BACKGROUND: In several species there is strong evidence that the retinal dopamine turnover is influenced by retinal dark and light adaptation. In the human retina, dopamine has been found in amacrine and interplexiform cells. METHODS: In the present study, the influence of orally administered levodopa on the human dark adaptation was investigated in healthy subjects using the Goldmann-Weekers adaptometer. To exclude effects of levodopa on the pupil size, a second group was examined after pupil dilation before each examination. A third and fourth group were examined under the same conditions as the first two groups, but without levodopa administration. RESULTS: Levodopa caused a uniform threshold elevation throughout dark adaptation with undilated and dilated pupils. No effect on sensitivity was observed in the control groups. CONCLUSION: These results show a dopaminergic reduction in sensitivity during human dark adaptation.
BACKGROUND: In several species there is strong evidence that the retinal dopamine turnover is influenced by retinal dark and light adaptation. In the human retina, dopamine has been found in amacrine and interplexiform cells. METHODS: In the present study, the influence of orally administered levodopa on the human dark adaptation was investigated in healthy subjects using the Goldmann-Weekers adaptometer. To exclude effects of levodopa on the pupil size, a second group was examined after pupil dilation before each examination. A third and fourth group were examined under the same conditions as the first two groups, but without levodopa administration. RESULTS:Levodopa caused a uniform threshold elevation throughout dark adaptation with undilated and dilated pupils. No effect on sensitivity was observed in the control groups. CONCLUSION: These results show a dopaminergic reduction in sensitivity during human dark adaptation.