Nearsighted Eyes See Better Underwater

A very nearsighted person can see more or less normally underwater because the faulty refractive index of the eye is partly negated by the water's refractive index. On land, myopia makes distant objects blur because the cornea bends light too strongly at the air–cornea boundary, so images focus in front of the retina. Underwater, the cornea loses much of that refractive power because water has a similar refractive index to the cornea, which cancels some of the eye's over-focusing.

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