Asked by: Lucy Haddacks, Norwich
The only living cells in the body that aren't directly served by blood vessels are those of the cornea in the eye. Oxygen and nutrients instead diffuse directly from the tear fluid on the outside and the aqueous humour (the thick watery substance between the lens and the cornea) on the inside, as well as along the nerve fibres that are connected to the cornea.
One of the problems with contact lenses is that they reduce the oxygen supply from the outside. Even with gas-permeable lenses, this can cause corneal neovascularisation, where blood vessels grow into the cornea. This problem is reduced or eliminated by the newest silicone hydrogel lenses. As well as the cornea, other areas of the body that don't have blood vessels include hair, nails, tooth enamel and the outer skin layers.
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