Which two factors are the main contributors to decreased dark adaptation in elderly?

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

Answer: (A)

Dark adaptation relies on the rods in the retina and the rapid regeneration of rhodopsin after it’s bleached by light. In older individuals, two main factors slow this process: cataracts, which cloud the lens, reduce the amount and quality of light reaching the retina, and thus blunt the rod signal needed for twilight and night vision; and decreased formation or slower regeneration of rhodopsin in the rods, which delays the restoration of rod sensitivity after exposure to bright light. Cone pigment (iodopsin) is involved in daylight and color vision, not the night-time adaptation that primarily uses rods, so its reduced formation isn’t the driving factor here. Glaucoma affects nerve transmission rather than the photochemical steps of dark adaptation, so it’s not the primary contributor. Therefore, cataracts plus slower rhodopsin production best explain the age-related decrease in dark adaptation.