Here the least converging power of eye lens is given as 20 dioptres behind the cornea. If we can calculate the maximum converging power, then we can get the range of accommodation of a normal eye. (a) To see objects at infinity, the eye uses its least converging power = 40 + 20 = 60 dioptres ∴ Approximate distance between the retina and the cornea eyelens = focal length of the eyelens = $\frac{100}{P}$ = $\frac{100}{60}$ = $\frac{5}{3}$ cm (b) To focus object at the near point on the retina, we have u = − 25 v = $\frac{5}{3}$ cm ∴ Focal length f should be given by $\frac{1}{f}$ = $\frac{1}{v} - \frac{1}{u}$ = $\frac{3}{5} + \frac{1}{25}$ = $\frac{15+1}{25}$ = $\frac{16}{25}$ ⇒ f = $\frac{25}{16}$ cm ∴ Corresponding converging power = 64 dioptres Power of the eyelens = 64 – 40 = 24 dioptres Thus the range of accommodation of the eyelens is approximately 20 to 24 dioptres.