Mammoth Memory

Myopia and correction

Myopia means that a person is short-sighted. A person's sight is good at short distances.


A person who is short-sighted can focus clearly on near objects but cannot focus on distant objects. Distant objects are blurry.

This is caused when an eyeball grows too long or the cornea becomes too steeply curved.

Distant blurry image on retina of short sighted person

Myopia – light rays focus too far in front of the retina. The retina only receives a blurry image.

Here we can see the light is focused in front of the retina and not on it, which will make the image look blurry.


If it could, the lens would need to get flatter and therefore thinner so that light does not refract as much. So the problem is as follows:

Convex lens too thin to focus the image

The way to get the image to focus on the screen is to use a concave lens in front of the convex lens.

Concave lens used in conjunction with a convex lens to focus an image

The effect of using a concave lens in front of a convex lens is to move the image to the point where it focuses on the screen. This has exactly the same effect as putting a concave lens in glasses in front of an eye that suffers from myopia when you need to see objects at distance.

Concave lens of glasses used to focus image on eyes retina

Using a concave lens in a pair of glasses lengthens `di` (image distance) to the point where it focuses on the retina.



Sight short is great
Use concave glasses (lens)


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