TOPICAL LEVODOPA-CARBIDOPA EYE DROPS FOR MYOPIA CONTROL: A PILOT STUDY IN A RABBIT MODEL OF FORM-DEPRIVATION MYOPIA

Objective: Dopaminergic drugs may be repurposed to modulate ocular growth. Our study aims to evaluate the safety, stability, and efficacy of a novel levodopa-carbidopa topical ophthalmic formulation for controlling myopia progression in the form-deprivation myopia (FDM) rabbit model. Methods: A 4:1 molar ratio of levodopa to carbidopa was formulated into an eye drop with a pH of 5.8 and stored at 4 °C in light-protected glass containers. We used 14 New Zealand white rabbits, which received form-deprivation myopia induction and were divided into two groups: seven into the control group and the other seven into the intervention group, the latter receiving treatment with the prepared levodopa-carbidopa formulation. Ocular safety was assessed using a slit-lamp exam, Schirmer’s test, and behavioral observations. Efficacy was represented by axial length and refraction, with retinal tissues being harvested for ELISA quantification of dopaminergic markers. Results: Levodopa-carbidopa formulation remained clear and stable with no visual signs of microbial contamination or degradation during the study period. No signs of ocular irritation or systemic toxicity were observed. Schirmer’s test values showed no significant difference pre-and post-treatment, proving the absence of drug-induced ocular irritation (p>0.05). Treatment with levodopa–carbidopa significantly inhibited axial elongation (18.16 mm vs. 23.12 mm, p = 0.013) and reversed myopic refractive error (4.57±1.06 vs. 2.64±1.41, p = 0.013) compared to the control group. Retinal tyrosine hydroxylase (TH) and dopamine receptor D2 (D2R) expression were significantly elevated in the treated group (p = 0.006 and p = 0.036, respectively), supporting enhanced dopaminergic signaling. Conclusion: Topical levodopa–carbidopa is a stable, well-tolerated formulation that suppresses progression of myopia in a rabbit model. The therapeutic effect is associated with enhanced retinal dopamine activity. These findings further support a pharmacologic strategy for myopia control.