Which option most accurately summarizes the two main causes of decreased dark adaptation in older adults?

• A. Cataracts and decreased rhodopsin formation
• B. Cataracts and decreased iodopsin formation
• C. Glaucoma and cataracts
• D. Decreased rhodopsin and iodopsin formation

Answer: (A)

Dark adaptation depends on the rod system and the regeneration of the rod pigment, rhodopsin. In older adults, two things blunt this process: the lens becomes more opaque (cataracts), which blocks and scatters light before it even reaches the retina, and the production/regeneration of rhodopsin in the rods slows down with age. With less light reaching the retina and slower rhodopsin recovery after exposure to bright light, the eye’s ability to adapt to darkness is reduced.

The other options don’t fit as well because iodopsin is the cone pigment used for bright-light and color vision, not for dark adaptation; glaucoma is an optic nerve/retinal disease not a primary cause of delayed dark adaptation; and decreased rhodopsin alone without cataracts wouldn’t fully explain the common age-related drop in dark adaptation seen clinically.