(a)When the eye lens is fully relaxed , u = ∞

The retina is 2 cm behind the eye-lens,hence v = 2 cm = 0.02 m

Using lens formula –

Substituting the values-

Hence, the power of the eye lens is

So, when the eyes are fully relaxed condition, eye lens has a power of 50 D

(b)When the eye lens is strained-

Distance of object u = – 25 cm = – 0.25 m

Using lens formula –

Substituting the values-

Hence, power of the eye lens becomes-

So, when the eyes are most strained condition, eye lens has a power of 54 D.