Will a nearsighted person who wears corrective lenses in her glasses be able to see clearly underwater when wearing those glasses?
closed as off-topic by Kyle Kanos, WillO, Jon Custer, eranreches, M. Enns Jun 7 at 18:53
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When light moves from one medium to another, the light refracts, meaning that it changes its direction of travel slightly. A nearsighted person would use a concave lens to correct for their nearsightedness. The lens would spread out the light coming through the lens. These lenses are designed so that the glasses correct for the nearsightedness so that the light ends up in the correct spot in the eye.
There's something called the refractive index and based on the difference between the refractive indices in two mediums, the refraction angle, meaning the angle at which the light travels after it has been refracted, will change.
The glass' lens is designed to work with the difference in refractive indices of air and glass, but when the air is replaced with water, the difference is less. Because the difference is less, the light will refract differently.
This difference in how the light refracts between water and glass, compared to air and glass, means that glasses would not correct your vision underwater, because the glasses would not put the light on a correct path into the eyes to create a clear image.
EDIT: As Poutnik points out, the glasses would work if you were wearing a mask that covered both the glasses and the eyes in air.