The discovery of a light-dependent molecular pathway that regulates how blood vessels develop in the eye suggests that light therapy could help premature babies, whose eyes are still developing, avoid vision problems. Called the opsin 5-dopamine pathway, it helps ensure that blood-vessel development in the eye is appropriately balanced, but it can be thrown out of balance when a baby is born prematurely. The study, a collaboration of research institutions in the United States and Czech Republic, was led by Richard Lang’s team at Cincinnati Children’s Hospital Medical Center. The researchers studied eye development and the influences of the opsin 5-dopamine pathway in postnatal mice and demonstrated in their mouse models that the developing postnatal eye depends on light responses in the retina that are controlled by opsin 5. Lang said opsin 5 is highly conserved in the chain of species evolution, enhancing the potential relevance of these findings for humans. To show what would happen without the balancing influence of opsin 5, researchers studied genetically modified mice that did not express the OPN5 protein in the retina. Loss of opsin 5 was found to increase levels of dopamine in the vitreous, causing blood vessels in the still-developing eyes to regress, hindering normal eye development. This microscopic image shows light-sensitive opsin proteins in the retinal ganglia nerve fibers of the neonatal mouse eye, helping scientists identify the role and importance of opsin proteins (such as OPN4 and OPN5) in the developing neonatal eye. Researchers are looking for light-based therapies that might prevent or treat eye diseases such as retinopathy of prematurity in premature babies or the condition myopia. Courtesy of Cincinnati Children’s. To test the influence of light stimulation, the researchers used 380-nm violet-colored light to activate signaling via opsin 5. This reduced dopamine levels in the eye and produced other molecular changes that helped restore proper timing cues needed for appropriately balanced vascular development. Previous studies have suggested that violet light and dopamine could be key regulators of eye development. Although the findings in the current study require additional research to become clinically relevant to humans, the data demonstrate that balanced coordination in the opsin 5-dopamine pathway is important to healthy eye development in baby mice, and possibly in human babies. “Our study indicates opsin 5-dopamine pathway is probably part of a light-dependent disease process for conditions like myopia, which is now a worldwide epidemic,” said Lang, who is the director of the Visual Systems Group at Cincinnati Children’s. “It raises the interesting possibility that we might be able to use light exposure to treat conditions like retinopathy of prematurity after a premature infant is born or in people with myopia.” The research was published in Nature Cell Biology (https://doi.org/10.1038/s41556-019-0301-x).