Question

What is myopia (or short sightedness)? What is the cause of this defect? How can this defect be minimized? Explain drawing a ray diagram.

Answer 1

Hint: We must be aware that myopia is a defect caused in vision due to this an individual cannot see nearby objects. This is a defect caused by the elongation of the eyeball. Which is related to the change in focus of the eye as the dimension of a lens changes. This defect is commonly seen in children.

Complete step by step answer:
So let us discuss what is myopia and how it is caused by the help of a ray diagram. Myopia is a vision defect, where a person cannot see distant objects distinctly after a limit but can see nearby objects.

Generally, Myopia is caused due to two reasons.

(I) The variation happens in the distance between the eye lens and the retina as it becomes larger when the eyeball gets elongated along its axis.
(II) If the curvature of the cornea is larger, then it will affect the refraction of light into the eye and results in making the focal length of the eye lens too small.

As we can understand from the diagram, the parallel rays coming from an object at infinity is forming an image not on the retina but slightly in front of it but there is no problem for image formation of nearer objects.

Now we will look at how a myopic eye could be treated. A myopic eye can be corrected by use of a concave lens of focal length which is equal to the far point F from the eye. So, this concave lens diverges the parallel rays from distant objects as if they were coming from the far point F. Then the eye lens produces a clear image.

Note:
We can simply understand the concept of myopia if we take the example of a single convex lens. If we look at images formed by a particular lens and then if we change the radius of curvature of the lens it will also change the focal length. It is like using an entirely new lens. This is what happens in a myopic eye. So, to neglect this we can introduce more paths to the incoming ray by using a concave lens.