When a person can see nearer objects distinctly but not distant ones, he is said to be suffering from myopia. In this case the convexity of the lens of his eye cannot be sufficiently decreased to form the image of the distant object on the retina. It is remedied by the use of concave glasses.
When a person can see distant objects clearly but not the nearer he is said to be suffering from hypermetropia. It is remedied by the use of convex glasses.
The person can see vertical lines clearly but not the horizontal ones, or vice versa. It is remedied by the use of cylindrical glasses.
(iv) Colour blindness:
If a person cannot distinguish between different colours (especially between red and green), he is said to be suffering from this defect.
(d) Sense of smell:
This is due to the presence of smell perceiving cells present in the lining of the nasal chambers.”
(e) Sense of hearing:
It is due to the movement of ear drum by the sound waves.