Question

A person is unable to see objects distinctly placed within 75 cm from his eyes.

a) Name the defect of vision the person is suffering from.

b) List its two possible causes.

c) Calculate the power of the lens needed to correct this defect. Assume that the near point for the normal eye is 25 cm.

Answer 1

(a) Hypermetropia or long sightedness.

(b) Two possible causes: 

• Curvature of eye lens decreases. 
• Shortening of eye ball.

(c) Given, u= -25 cm, v= -75 cm, f= ? 

1/f = 1/v- 1/u 

f = 37.5 cm 

P = 100/f 

= +2.67 D