In aging, decreased dark adaptation is due to cataracts and which rhodopsin-related change?

In aging, decreased dark adaptation is due to cataracts and which rhodopsin-related change?

• A. Decreased formation of rhodopsin
• B. Decreased formation of iodopsin
• C. Both rhodopsin and iodopsin
• D. Increased rhodopsin formation

Answer: (A)

Dark adaptation relies on rod vision and the regeneration of rhodopsin after it’s bleached by light. With aging, the process that forms rhodopsin can be reduced, so there are fewer rhodopsin molecules ready to respond in low-light conditions. This makes night vision slower and less sensitive, even when cataracts are present. Iodopsin is the cone pigment important for color and daylight vision, not the primary driver of dark adaptation, so changes in its formation don’t explain the decrease. Increased rhodopsin formation would actually enhance night vision, which isn’t observed here.

Dark adaptation relies on rod vision and the regeneration of rhodopsin after it’s bleached by light. With aging, the process that forms rhodopsin can be reduced, so there are fewer rhodopsin molecules ready to respond in low-light conditions. This makes night vision slower and less sensitive, even when cataracts are present. Iodopsin is the cone pigment important for color and daylight vision, not the primary driver of dark adaptation, so changes in its formation don’t explain the decrease. Increased rhodopsin formation would actually enhance night vision, which isn’t observed here.