The eye is the first component of the sensory system of vision. Despite its small size, the eye is a very complex organ. The retina performs the first stage in visual perception. The optic nerve and the visual cortex of the brain are the next stages of visual perception.
Light enters the eye and passes through the cornea, the aqueous humor, lens and vitreous humor. It ultimately reaches the retina, the light-sensor of the eye.
Color vision is possible due to cones called cone pigments, which contain color responsive pigments. There are three kinds of color-sensitive pigments namely, Red-sensitive pigment, Green-sensitive pigment and Blue-sensitive pigment. Each cone has a pigment sensitive to the corresponding color.
Color blindness occurs when a cone does not function properly. This causes the inability to differentiate between colors. People suffering from color blindness may be able to see red or green, but confuse the two colors. This disorder affects men more than women. It is an inherited disorder.
Normal vision, known as vision or visual acuity, is the ability of a human being to read a Snellen eye chart from a distance of 20 feet. This is termed as 20/20 vision. A 20/40 vision is when a person stands 20 feet away from the chart, and can see what most people can see when standing 40 feet from the chart. In the United States, a vision of 20/200 is considered as legal blindness.
The general process of visual perception is universal and independent of any culture or race. It is also clear that individual differences such as impairment of sight and spatial skills also affect our visual perception.