Which factor is NOT a main contributor to decreased dark adaptation in the elderly?

Which factor is NOT a main contributor to decreased dark adaptation in the elderly?

• A. Cataracts and decreased rhodopsin
• B. Cataracts and decreased iodopsin
• C. Cataracts and increased pupil size
• D. Decreased rhodopsin and iodopsin formation

Answer: (C)

Dark adaptation in dim lighting relies mainly on the rod system and the regeneration of rhodopsin. Anything that reduces the amount of light reaching the retina or lowers the rod pigment available for phototransduction will impair this process. Cataracts scatter and absorb light, so less light gets to the retina, directly blunting dark adaptation. A age-related drop in rhodopsin formation further diminishes the rod’s sensitivity to light, making adaptation to darkness slower. Loss of iodopsin, the cone pigment, mainly affects cone-mediated vision, which is more important in bright conditions, but its decreased formation can still contribute to overall photosensitive performance, especially in mixed lighting. When both rhodopsin and iodopsin formation are reduced, both rod and cone pathways are less capable of adjusting to changing light levels, which further impairs adaptation. Increased pupil size would actually allow more light into the eye and would tend to improve dark adaptation. However, in the elderly, pupils are more likely to become smaller (senile miosis), which reduces retinal illumination and worsens dark adaptation. Therefore, increased pupil size is not a main contributor to decreased dark adaptation.

Dark adaptation in dim lighting relies mainly on the rod system and the regeneration of rhodopsin. Anything that reduces the amount of light reaching the retina or lowers the rod pigment available for phototransduction will impair this process.

Cataracts scatter and absorb light, so less light gets to the retina, directly blunting dark adaptation. A age-related drop in rhodopsin formation further diminishes the rod’s sensitivity to light, making adaptation to darkness slower. Loss of iodopsin, the cone pigment, mainly affects cone-mediated vision, which is more important in bright conditions, but its decreased formation can still contribute to overall photosensitive performance, especially in mixed lighting. When both rhodopsin and iodopsin formation are reduced, both rod and cone pathways are less capable of adjusting to changing light levels, which further impairs adaptation.

Increased pupil size would actually allow more light into the eye and would tend to improve dark adaptation. However, in the elderly, pupils are more likely to become smaller (senile miosis), which reduces retinal illumination and worsens dark adaptation. Therefore, increased pupil size is not a main contributor to decreased dark adaptation.