A growing foetus is sheltered from the outside world, but external conditions may still affect it. Only a tiny amount of light manages to get inside the womb, but new evidence suggests this may be essential to ensure eyes develop correctly. Inside each growing eye, a cup-shaped network of blood vessels forms to supply the early retina with oxygen and nutrients. After birth these vessels are no longer needed, so they slowly break down. The left-hand image shows the pattern of vessels (stained blue) in the eye of a healthy eight-day-old mouse. In genetically engineered mice that lack the light-absorbing protein melanopsin (right-hand image) the vessels fail to break down normally post-birth, persisting as a dense, tangled mess. Exactly the same thing happens if a foetus grows in total darkness. This discovery may help to explain certain eye abnormalities, although the influence of light during human pregnancy is still unknown.
Written by Emma Stoye
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