Water acts as a magnifier, so anything viewed from above the water will seem larger and every time your head moves from in and then out of the water, this magnification and de-magnification will occur. If you are far-sighted or near-sighted, this will be complicated by the magnification of the water.

When prescription swim goggles or dive masks are worn underwater, the visual acuity that the wearer experiences is still far less than they would experience above ground with regular prescription glasses.