Question

the distance between the eye lens and the retina for healthy eye​

Answer 1

the distabce between the eye lens and retina for healthy eye is 20mm

Answer 2

The distance between the lens and retina of a normal and healthy eye is 20 mm.

When a particular object is located at infinity( far away from the eye), the image is essentially formed at the focal point.

Hence, when the muscles of the eye are in the relaxed state, the focal length of the lens and the cornea should also be about 20 mm.