Why can vitamin A deficiency cause night blindness?

Vitamin A deficiency causes night blindness because the vitamin is essential for the production of rhodopsin, a light-sensitive pigment found in the rod cells of the retina.41

Rhodopsin is composed of a protein called opsin combined with 11-cis-retinaldehyde, a derivative of vitamin A. These rod cells are responsible for vision in dim light. When vitamin A levels are low, the eye cannot produce sufficient amounts of 11-cis-retinaldehyde, leading to reduced levels of rhodopsin. This deficiency impairs the eye's ability to adapt to darkness, resulting in the reduced capacity to see in dim light or at night.2341

Fortunately, this condition is typically not permanent; vision often recovers once adequate levels of vitamin A are restored to the body.43