Library · Physiology
Night vision
Make it clearer
At night the eye does not see with the same cells it uses by day. The photoreceptors of the retina, the cells that turn light into a signal, are not all alike: cones work in bright light. Rods are the ones that make vision possible in dim light, and that low-light vision is called scotopic.
Rods have a single light-sensitive pigment, rhodopsin. It is made of two parts: a protein called scotopsin and retinol, which is a form of vitamin A.
That detail explains something we have all noticed. With a single pigment there is no way to tell colors apart: rods are achromatic. Color and fine detail both come from the cones, and cones need more light. That is why at night everything appears in shades of gray.
And that is why vitamin A matters so much here. When intake falls, the available 11-cis-retinal can drop, dark adaptation can break down, and night blindness, known in medicine as nyctalopia, can appear.
In brief
Seeing in low light, or scotopic vision, depends on the rods, the retinal photoreceptors that make vision possible in dim light.
Rods have a single photopigment, rhodopsin, made from the protein scotopsin and retinol, which comes from vitamin A.
With only one pigment they are achromatic; color and acuity come from the cones, which need more light.
Low vitamin A intake can lower 11-cis-retinal, impair dark adaptation, and show up as night blindness, or nyctalopia.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Night Vision, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
Updated