Narrowband Blue and Green Light Are Associated with Opposing Refractive Effects and Dopamine Signaling in Guinea Pigs

Purpose To investigate the effects of narrowband blue and green light on refractive development in guinea pigs and to explore the associations of retinal and serum dopamine (DA) and melatonin. Design Experimental animal study. Participants Seventy-two 2-week-old pigmented male guinea pigs. Methods Animals were randomly assigned to white (5000 K), blue (430 nm), or green (530 nm) light for 12 weeks. A longitudinal cohort (n=15 per group) underwent biweekly measurements of refractive error, axial length (AL), and choroidal thickness (ChT). Separate terminal cohorts were euthanized at weeks 0, 4, and 12 (n=3 per group per time point) for measurement of serum and retinal dopamine (DA), melatonin, and scleral type I collagen. In vitro, primary scleral fibroblasts were treated with DA, melatonin, and pathway inhibitors to assess cAMP, cGMP, and type I collagen levels. Main Outcome Measures Refractive error, axial length, choroidal thickness, retinal and serum dopamine and melatonin levels, scleral type I collagen content, and in vitro type I collagen levels. Results In the longitudinal cohort, at 12 weeks, blue light exposure shifted refractive development toward greater hyperopia (+1.67 ± 0.14 D) and reduced AL elongation (−0.08 ± 0.07 mm) compared with white and green light (both P < 0.001), while green light exposure shifted refractive development toward greater myopia (−2.42 ± 0.14 D) and AL elongation (+0.69 ± 0.11 mm). ChT increased under blue light (+14.80 ± 10.35 μm) and decreased under green light (−19.25 ± 4.39 μm; P < 0.001). In the separate terminal cohorts, blue light was associated with significantly higher serum and retinal DA levels at 4 and 12 weeks compared with white and green light ( P < 0.05). Melatonin levels showed no sustained intergroup differences. In vitro, DA increased type I collagen levels, an effect enhanced by adenylyl cyclase inhibition, whereas melatonin reduced type I collagen levels. Conclusions Narrowband blue and green light are associated with opposing refractive and axial growth patterns in guinea pigs, accompanied by differences in dopamine levels and scleral collagen content. These findings support a dopamine-related contribution to wavelength-dependent refractive development and suggest that spectral composition may influence ocular growth. Further studies are needed to establish causality and evaluate translational potential for myopia prevention.