Colour blindness (colour vision deficiency) is a condition in which certain colours cannot be distinguished, and is most commonly due to an inherited condition.

Cones (colour sensitive receptors) containing single visual pigments selective for red, green, and blue light, are present in the normal human eye.

Disturbances of colour vision will occur if the amount of pigment per cone is reduced or if one or more of the three cone systems are absent.

Protanomaly is referred to as "red-weakness", an apt description of this form of colour deficiency.

Deuteranomalous person adjust your television and he would add more green and subtract red. He is considered "green weak".

Nyctalopia (Greek for "night blindness") is a condition making it difficult or impossible to see in relatively low light. It is a symptom of several eye diseases.

Night blindness may exist from birth, or be caused by injury or malnutrition (for example, a lack of vitamin A).

The outer area of the retina is made up of more rods than cones. The rod cells are the cells that enable us to see in poor illumination. This is the reason why loss of side vision often results in night blindness.