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Vitamin A crystals. Polarized light micrograph of crystals of the fat-soluble antioxidant and trace nutrient vitamin A. It is also known as retinol. This vitamin is made in the body from precursor compounds obtained from sources such as milk, eggs and carrots. When converted to the retinal form in the body, this chemical is vital to the functioning of the eye's retina. Field of view size: 0.74 x 1.11 millimetres. (KEYSTONE/SCIENCE PHOTO LIBRARY/ANTONIO ROMERO/SCIENCE PHOTO LIBRARY)