In dark adaptation, there is:
Break down of rhodopsin
Increased threshold for vision
No role for cones
No change in the dioptric power of the eye
In dark adaptation, there is re-synthesis of the bleached rhodopsin. In the retina, the storage form of vitamin A (all-trans retinol) is conveed to 11-cis retinal which combines with opsin to form rhodopsin. Initial dark adaptation is due to cones; cones form visual pigment faster as compared to rods. Other changes in the dark: (1) dilation of pupil, (2) increased number of impulses in the optic nerve fibers.
Special Senses