Which condition leads to a reduced sensitivity to red light?

Protanopia is a type of color vision deficiency that specifically results in a reduced sensitivity to red light. This condition occurs due to the absence of the long-wavelength (L) photopigments in the cone cells of the retina, which are responsible for detecting red wavelengths. As a result, individuals with protanopia have difficulty distinguishing reds and greens and may perceive these colors as shades of gray or other colors.

In contrast, deuteranopia affects the medium-wavelength (M) photopigments, primarily impacting green sensitivity, and tritanopia involves the short-wavelength (S) photopigments, which affects blue sensitivity. Anomalous trichromacy refers to a condition where there is a mild defect in one of the three cone types but not a complete absence, which typically leads to altered color perception rather than a total lack of sensitivity to a particular color. Therefore, the specific impact of protanopia on red light sensitivity makes it the correct choice for this question.