James Crook

“The optical system of the eye cornea and lens is designed to bring point objects to a focus at a point. However the rods are not points, they are much longer than their diameter. The rod will gain in sensitivity if the light reaching it is collimated, that is travelling as a parallel beam rather than converging to a point and then diverging. The full length of the sensitive part of the rod will then be being used. If this is indeed what happens in human eyes, then the sensitivity lost through having additional layers of cells to pass through is more than made up for by the correct focusing of light onto the rods and cones by these additional cells themselves.”
― James Crook