In dark adaptation, there is:: (A) Break down of rhodopsin, (B) Increased threshold for vision, (C) No role for cones, (D) No change in the dioptric power of the eye
Answer is D. 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.