About vision: The human eye
The eye works much like a camera. Light enters the eye through the cornea
via the pupil at the center of the iris, the colored part of the eye.
The pupil controls the amount of light admitted while the cornea does
most of the focusing. Light then passes through the lens, where it is
finely focused, and travels back through the eye to the retina. The retina
interprets images and then sends the information to the brain via the
is sometimes referred to as the "window of the eye". It is composed of
5 layers of tissue. Its outer layer (the epithelium) provides protection
for the eye. The epithelium is made up of highly regenerative cells that
have the ability to grow back within 3 days, allowing for fast healing
of superficial injuries. Most of the inner layers of the cornea provide
strength to the eye.
This is the
black circle in the middle of the eye. The primary function of the pupil
is to control the amount of light entering the eye. When you're in a bright
environment, the pupil becomes smaller to allow less light through. When
it's dark, the pupil expands to allow more light to reach the back of
This is the
colored part of the eye surrounding the pupil. The primary function of
the iris is to control the size of the pupil. This is achieved through
contraction or expansion of the muscles of the iris.
is the white part surrounding the iris. The sclera's purpose is to provide
structure, strength, and protection to the eye.
The lens is the clear structure located behind the pupil. Its primary
function is to provide fine-tuning for focusing and reading. The lens
performs this function by altering its shape. At about the age of 45,
the lens becomes less flexible. At about the age of 65, the lens becomes
cloudy and hard, preventing light from entering the eye.
This is the clear gel-like substance located inside the eye's cavity.
Its purpose is to provide a spherical shape to the eye. The vitreous body
may develop small clumps known as 'floaters', which are especially common
in nearsighted people.
consists of fine nerve tissue which lines the inside wall of the eyes
and acts like the film in a camera. Its primary function is to transmit
images to the brain.
nerve carries images from the retina to the brain.