Impact of dopamine depletion on refractive development in guinea pigs under different light conditions

This study aimed to explore the effects of dopamine (DA) depletion on refractive development in guinea pigs under different light conditions using intravitreal injections of 6-hydroxydopamine (6-OHDA). On day 1, 6-OHDA was injected into the vitreous of guinea pigs. Retinal DA and its metabolite 3,4-dihydroxyphenylacetic acid (DOPAC), the retinal DOPAC/DA ratio, and vitreal DOPAC were measured by high-performance liquid chromatography-electrochemical detection (HPLC-ECD). Refractive error, axial length, and corneal curvature were assessed at baseline and at 1, 2, and 4 weeks post-injection. In Experiment 1, under normal ambient light, 6-OHDA suppressed retinal DA and its metabolite (all P < 0.05). Dopamine depletion resulted in myopic shifts due to steeper corneas, accompanied by shorter axial length compared with the vehicle group (all P < 0.05). In Experiment 2, Dopamine depletion consistently induced corneal steepening across wavelengths, but axial length effects were wavelength-dependent: inhibition under white light, amplification of elongation under green light, and further shortening under blue light. The results suggest that corneal curvature regulation may involve DA-dependent mechanisms, whereas axial length control may involve DA-independent pathways.