Besides cataracts, which biochemical change is implicated in reduced dark adaptation in older adults?

Besides cataracts, which biochemical change is implicated in reduced dark adaptation in older adults?

• A. Decreased rhodopsin formation
• B. Decreased iodopsin formation
• C. Both
• D. Increased macular pigment density

Answer: (A)

Dark adaptation is driven by the rod system and the visual pigment rhodopsin. After light exposure, rhodopsin is bleached and must be regenerated in the dark; in older adults, this regeneration is less efficient, so fewer rhodopsin molecules are available in rods. That slower replenishment directly reduces sensitivity in low light, making dark adaptation impaired. Iodopsin forms in cones and supports color and daylight vision; its formation is not the limiting factor for adapting to darkness, so decreased iodopsin formation wouldn’t explain the observed reduction in dark adaptation. Macular pigment density relates to blue-light filtering and central vision but doesn’t govern the biochemical regeneration of rod photopigment, so changes there aren’t the primary cause of reduced dark adaptation.

Dark adaptation is driven by the rod system and the visual pigment rhodopsin. After light exposure, rhodopsin is bleached and must be regenerated in the dark; in older adults, this regeneration is less efficient, so fewer rhodopsin molecules are available in rods. That slower replenishment directly reduces sensitivity in low light, making dark adaptation impaired.

Iodopsin forms in cones and supports color and daylight vision; its formation is not the limiting factor for adapting to darkness, so decreased iodopsin formation wouldn’t explain the observed reduction in dark adaptation.

Macular pigment density relates to blue-light filtering and central vision but doesn’t govern the biochemical regeneration of rod photopigment, so changes there aren’t the primary cause of reduced dark adaptation.