Question

The diagram alongside represents a certain defect of vision of the human eye.
Figure

(i) Name the defect.
(ii) Describe briefly the condition in the eye responsible for the defect.
(iii) Redraw the figure by adding a suitable lens correcting the defect. Label the parts through which light-rays pass.
(iv) What special advantage do human beings derive in having both eyes facing forward?

Answer 1

(i) The defect is known as long-sightedness, or hypermetropia.

(ii) The defect occurs for the following reasons.

• Flattening of the lens
• Shortening of the eyeball from front to back

(iii) The defect can be rectified using convex lenses.


(iv) The forward-facing eyes of humans help them to see an object with two eyes at the same time, with both eyes set in the same plane. When signals from the two eyes reach the brain, they are superimposed and processed into a single picture with depth. As a result, humans get a 3D picture and are able to judge distances well.