Question

what is near sightedness? State its any two causes. Explain with diagram that how it can be corrected​

Answer 1

Answer:

Near sightedness is also myopia. Due to decrease in the focal length of the eye lens. Myopia can be corrected by using a concave lens of suitable focal length in the spectacles of such a person. The ability of the eye lens to adjust its focal length is called automatic accommodation.

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Answer 2

Answer :

$\underline{\red{\mathcal{NEAR-SIGHTEDNESS\:\:OR\:\:MYOPIA\::}}}$

When a person can see near object clearly but can't see the objects beyond a certain distance clearly, then such a defect of vision is called near-sightedness or myopia.

In this defect the far point of eye is displaced closer to eye. In the figure (attachment fig.) an eye suffering from myopia is shown in which rays coming from infinity are focused at a point in front of retina. So, eye lens is unable to make a distinct Image on retina.

$\underline{\red{\mathcal{CAUSES\:OF\:MYOPIA\::}}}$

This defect is caused due to following two reasons :

• It may occur due to increase in curvature of eye lens due to which focal length of eye lens is reduced.
• It may occur due to the increase in the diameter of the eye ball, due to which the distance between eye lens & retina is increased.

$\underline{\red{\mathcal{CORRECTION\::}}}$

This defect can be corrected by using a concave lens, which can make the Image of a far distant object at the new position of far point of eye [Point P in figure]. In this position the rays entering the eye lens appear as if they are coming from the point P. After getting refracted through the eye lens, these rays are focused on yellow spot of retina so that a distinct Image is seen.