Exposure to light in the womb is essential for unborn babies to develop healthy eyes, according to new research.

Eyes depend on light to see, and a new study on mice found that the eyes also need light for healthy development during pregnancy.

Scientists say that the finding, published in the journal Nature, offers a new basic understanding of fetal eye development and eye diseases caused by vascular disorders such as retinopathy of prematurity (ROP) that can blind premature infants.

"This fundamentally changes our understanding of how the retina develops," study co-author Richard Lang, a researcher in the Division of Pediatric Ophthalmology at Cincinnati Children's Hospital Medical Center said in a statement.

"We have identified a light-response pathway that controls the number of retinal neurons," Lang added. "This has downstream effects on developing vasculature in the eye and is important because several major eye diseases are vascular diseases."

Scientists explained that because several stages of eye development occur after birth, it was always assumed that the role light played in the development of the eye would also happen only after birth.

After experimenting on mouse models, researchers from the Cincinnati Children's Hospital Medical Center and the University of California, San Francisco, found that the activation of the newly described light-response pathway happens during pregnancy to activate the developmental process that produces a healthy eye. More specifically, researchers say that it is important for a sufficient number of photons to enter the mother's body by the late stages of pregnancy.

The study found that photons of light activate a protein called melanopsin directly in the fetus to help trigger normal development of blood vessels and retinal neurons in the eye.

Researchers explain that one purpose of the light-response pathway is to hold back the number of blood vessels that form in the retina. Researchers explain that while these vessels are critical to retinal neurons, which need large amounts of oxygen to form and to function, when they grow unchecked, retinopathy of prematurity can occur. The continued expansion of blood vessels in the eye would then put extreme pressure on the developing eye, and in extreme cases could lead to severe damage and blindness.

To study the specific components and function of the light-response pathway, researchers conducted several experiments on laboratory mice.

Researchers found that mice reared under dark conditions from late gestation and those with a mutated opsin gene that produces melanopsin, an essential protein in eye development, showed evidence of overgrowth of hyaloid vessels and abnormal retinal vascular growth.

Researchers explained that the unchecked growth of blood vessels was driven by the protein vascular endothelial growth factor called Vegfa. However, when the light response pathway was properly engaged, it controlled Vegfa to help prevent promiscuous vascular growth.

Researchers said that the latest findings could apply to people because the melanopsin protein is present in both mice and humans during pregnancy.

Scientists are now studying how the light-response pathway might affect the risk of retinopathy of prematurity in pre-term infants as well as other eye diseases.

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