Question

A student is unable to see clearly the words written on the black board placed at a distance of approximately 3 m from him. Name the defect of vision the boy is suffering from. State the possible causes of this defect and explain the method of correcting it.

Answer 1

There are two defects of vision, Farsightedness and Nearsightedness. Hypermetropia is corrected by using a concave lens. Myopia is corrected by using a convex lens.

Complete step by step answer:
As the student is not able to see nearby objects clearly so he is suffering from farsightedness or hypermetropia. It is a defect of vision in which a person is not able to see nearby objects clearly. This defect causes the inability of the eye to focus on nearby objects. In such cases the lens' power of eyes to refract light is diminished and the images of nearby objects are focused at a location behind the retina. The light-detecting nerve cells are located on the retinal surface As the image is not focused properly in such cases. These nerve cells thus detect a blurry image of nearby objects. Such defects are corrected by using a converging lens. It will refract light before entering the eye and decreases the distance of the image. So, this defect of vision is corrected by using a concave lens of suitable focal length.

Note:
Hypermetropia is a common eye condition where nearby objects appear blurred, on the other hand Myopia is a common eye condition where distant objects appear blurred. A hypermetropic person is not able to see nearby objects but able to see distant objects clearly. On the other hand a myopic person is not able to see distant objects but able to see nearby objects clearly. Hypermetropia is corrected by using a concave lens. Myopia is corrected by using a convex lens.