Human eye has a marvelous range of sight. We can see as clearly during the bright day as we can see during the night. Considering the fact that our eye is like a camera, we can easily understand how our eyes adjust to the different levels of light as quick as possible.
Parts of the Eye Responsible for Eye Vision
There are three major components in the eye that are responsible for letting us see in the dark:
1. Pupil of the Eye
The pupil is the opening in the eye, located in the middle of the iris. It appears as a bright black spot within the iris. Its appearance is black in color so that the light entering the pupil can be completely absorbed by the tissues located within the eye.
Pupil has the ability to contract and dilate involuntarily, so as to adjust the intensity and amount of light that enters or leaves it. This ability of the pupil is termed as the pupillary reflex. For the very reason, the pupil extremely contracts in the presence of bright light in order to block extra light from entering. In case of night vision, it dilates to its maximum, allowing maximum light exposure in order to see in the dark.
2. Rods and Cones of the Retina
The two major type of cells found in the retina are termed as rods and cones. The cones are the type of cells in the retina which are responsible for our colored vision, whereas the rods are responsible for the black and white images. It is the rod cells that are important for the night vision for they are primarily responsible for working in low light.
The main element responsible for night vision is a chemical compound found in the rod cells named Rhodopsin. It is a compound used by rods for the perception of light by absorption of protein. Whenever a Rhodopsin compound absorbs photon to perceive light, it breaks up into two molecules, Retinol and Opsin respectively. These molecules however, take their time to fuse back into Rhodopsin slowly.
Therefore, when one is in the presence of the bright light, the Rhodopsin splitting continues at a regular rate. However, if the lights are suddenly turned off, it takes several minutes for the eye vision to adjust correspondingly to see in the dark. This happens because during the time of the presence of bright light, most of the Rhodopsin breaks up into its molecules, and now in the dark, there is not enough Rhodopsin to see clearly. But as soon as the fusion of the molecules back into Rhodopsin is complete, the night vision gets clearer.
The Retinol present in the eye is a byproduct of Vitamin A. Vitamin A is therefore, responsible for maintaining healthy vision. However, a Vitamin A deficiency can lead to Night Blindness or Nyctalopia, which is the inability to see in the dark or in poor light. Therefore, an intake of a rich Vitamin A diet is advised by eye doctors for healthy night vision.