Retinal Function in Young Adults Following Topical Application of Levodopa to the Eye

Purpose: Levodopa has been investigated as a therapeutic solution for ocular disorders involving dysregulation of the dopaminergic system, especially in the context of myopia. However, given the critical role dopamine plays in normal vision, this phase I trial examined whether levodopa/carbidopa eye drops induce any regional changes in retinal structure and function. Methods: Twenty-nine healthy male subjects 18 to 30 years of age were randomly assigned to receive either a low (1.4/0.34 μmoles/day, n = 14) or high (2.7/0.68 μmoles/day, n = 15) dose of levodopa/carbidopa eye drops in 1 eye for 28 consecutive days. A placebo solution was applied to all fellow eyes. Measures included visual acuity, regional frequency doubling perimetry, regional multifocal electroretinogram (mfERG) and optical coherence tomography (retinal thickness). Outcome measures were undertaken at baseline, end-of-treatment (4 weeks), and at a follow-up (4 months posttreatment). Results: For low dose treated eyes, regional analysis showed a small, statistically significant change in mfERG recordings (increase in ring 5 amplitude in low dose treated eyes, P < 0.05) and the retinal thickness map (localized retinal thinning in low dose treated eyes, P < 0.05). These changes were not clinically significant. No significant changes were observed in high dose treated eyes. Pharmacokinetic analysis (rabbits) demonstrated that levodopa was not detectable within blood and peaked within the eye at 15 to 30 minutes (and eliminated within 4 hours). Conclusions: No clinically significant effects of levodopa/carbidopa eye drops were found with regard to normal retinal structure and function following short-term use. Translational Relevance: This study further demonstrates the safety of topical levodopa, which may support its use in the treatment of ocular disorders in which the dopamine system is dysregulated.