Researchers at the NIH's National Eye Institute (NEI) have found that energy-producing organelles in the eye's photoreceptor cells, called mitochondria, function like microlenses that help channel light to the outer segments of these cells. where it is converted into nerve signals. The finding in ground squirrels provides a more accurate picture of the optical properties of the retina and could help detect eye disease earlier. The findings, published today in Science Advances, also shed light on the evolution of vision.