For a normal eye, the cornea of eye provides a converging power of 40 D and the least converging power of the eye lens behind the cornea is 20 D. Using this information, the distance between the retina and the cornea-eye lens can be estimated to be:

The effective power (Peff) of the cornea and eye lens is the sum of their individual powers:

Peff = Power of cornea + Power of eye lens
Peff = 40 D + 20 D = 60 D

The focal length (f) is the reciprocal of the power:

f = 1 / Peff = 1 / 60 D = 1/60 m

Converting meters to centimeters:

f = (1/60 m) * (100 cm/m) = 100/60 cm = 1.67 cm

Therefore, the distance between the retina and the cornea-eye lens can be estimated to be 1.67 cm.