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

Converging power of corneaPc=+40DLeast converging power of eye lens,Pe=+20DPower of the eye-lens,P=Pc+Pe=40D+20D=60DPower of the eye lensP=1Focal  length of  the  eye lensff=1P=160D=160m=10060cm=53cmDistance between the retina and cornea-eye lens= Focal length of the eye lens=53cm=1.67cm