6.1 Human Vision

Using optical systems, human vision can be corrected and extended.
What is human vision? Human eyes can focus on objects that are near or far and can also adapt to both sunlight at day or darkness at night.
How light enters the eye: Light enters the eye through the pupil. It is in the center and it appears dark in order to let light passes through the opening without reflecting back. The iris is a circle of muscle surrounding the pupil. It is the part with colour on one's eye being: brown, blue, green, hazel, or grey....etc. The iris also controls the amount of light from entering the eye. ex: When in very dim light, the iris expands in order to let more light to enter the pupil.
ex: When in very bright light, the iris contracts the pupil and reduce the amount of light from entering the eye.
Covering over the pupil and iris is a transparent tissue ( clear, allow light to pass through) called the cornea. It is made of cells that are transparent enough to allow light to pass through, but it's also tough enough to hold the eye together. Around the cornea is the sclera, an opaque tissue. It is the white part surrounding the iris.
Beneath the pupil lies a flexible convex lens. All the light rays must pass through the lens and are focused on a screen behind the eye called the retina, then an image of the object is formed. Some other cells in the retina convert the light rays into electrical signals which are sent to the brain through the optic nerve (the pair of nerves passing impulses from the eye to the brain)