How does vitamin A help the eye see in dim light?

Vitamin A is essential for vision in dim light because it is a key component of rhodopsin, a light-sensitive pigment found in the rod cells of the retina.12

Rhodopsin is composed of a protein called opsin and a pigmented molecule known as 11-cis-retinal, which is derived from vitamin A. When light strikes the retina, it triggers a process called photoisomerization, where the 11-cis-retinal is converted into all-trans-retinal. This structural change initiates a cascade that converts light into an electrical signal sent to the brain.234

In dim light, the eye relies on the regeneration of rhodopsin to maintain sensitivity. This process, known as dark adaptation, involves recycling the all-trans-retinal back into the 11-cis form so it can recombine with opsin. Because vitamin A is the precursor for this essential pigment, a deficiency leads to night blindness, as the eye lacks the necessary rhodopsin to effectively detect low levels of light.2513