How do glasses correct your vision? I know it has something to do with the retina but what exactly does it do?
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Imagine using a magnifying glass to burn some dried leaves. To concentrate the sunlight, you would move the magnifying glass back and forth until all that light hits a single point.
In a similar way our eyes need to bend the light coming into it so that the light rays can concentrate at a point at the back of our eyes (the retina) where the light-sensing cells are.
However the amount we need to bend light changes depending on how far the object we are looking at is. Light from closer objects need to be bent more than light from further objects. Our eye has a special lens (like the magnifying glass) to bend the light. To adjust how much the lens bends light, we have special muscles to pull or contract the lens which increases or decreases how much we bend the light (like using our arms to move the magnifying glass back and forth). However these muscles can weaken over time which prevents the eye properly bending the light to our retina.
Glasses compensate for this muscle weakness by bending the light a bit before it gets to your eyes so the muscles don’t have to do as much bending to get the object in focus.
This is also why people need different prescription lens – since some people will have weaker muscles than others and therefore they will need glasses that can do more (or less) of the light bending. And if a person has trouble seeing close things (myopia), they need glasses to help concentrate light (basically a magnifying glass) while a person who has trouble seeing far away things (hyperopia) will need glasses to help spread out light (the opposite of a magnifying glass). We have even designed glasses that can concentrate and spread light (bifocals) for people who have trouble with both.
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