Effects of Light of Different Spectral Composition on Refractive Development and Retinal Dopamine in Chicks

There is ample evidence that retinal dopamine (DA) is involved in the biochemical signaling cascade that controls emmetropization, but it is unknown how its release depends on the spectral composition of ambient light. We have studied DA release, refractive development, and growth in chicken eyes that were exposed to light of different spectral bands, and had either normal vision or were covered by frosted diffusers to induce myopia.

Experiment 1: After spending the night in the dark, chicks were exposed to white room light (spectral range, 430-630 nm) or kept in the dark. Additional chicks were unilaterally exposed to blue (peak at 470 nm), red (620 nm), or UV lighting (375 nm) for 30 minutes and their fellow eyes covered with black occluders to minimize light exposure. Experiment 2: In the second experiment, chicks wore diffusers over one eye to induce deprivation myopia and were raised for 5 days in either white room light or in lighting supplied by UV, blue, or red light-emitting diodes (LEDs). Refractive states were recorded daily with infrared photoretinoscopy, and ocular dimensions at the start and end of the experiment with A-scan ultrasonography. DA and its metabolites were measured in retina and vitreous by high pressure liquid chromatography-electrochemical detection (HPLC-ED) in all cases.

Compared to chicks kept in the dark, retinal DA and vitreal 3,4-dihydroxyphenylacetic acid (DOPAC) concentrations were clearly elevated after 30 minutes in white light. Vitreal DOPAC was also increased in red, blue, and UV lighting, compared to the fellow eyes covered with black occluders (black occluder versus blue light: 1.31 ± 0.32 vs. 1.70 ± 0.37; red: 1.26 ± 0.33 vs. 1.64 ± 0.38; UV: 1.13 ± 0.19 vs. 1.63 ± 0.21 ng/0.1 g wet weight). Chickens developed significantly less deprivation myopia, with shorter eyes, when raised under UV and blue lighting for 5 days, compared to under red and white light. Eyes with normal vision became more hyperopic in blue and UV lighting. Vitreal DOPAC levels were lowest after 5 days of exposure to UV lighting.

Red, blue, and UV lighting all stimulated the release of retinal DA, but there were wavelength-dependent differences in DA release and metabolism. Less deprivation myopia developed in UV and blue lighting, compared to white and red light. The application of these findings to humans is limited by the fact that, different from chicks, humans have very low sensitivity in the near-UV region of the spectrum.