The white part of the eye is
known as the sclera.
Light enters the eye
through the cornea, which is made of transparent tissue.
The cornea is one of the elements that provides focusing
power for the eye.
The pupil is the dark,
round opening in the center of the colored iris. It acts
as an aperture to regulate the amount of light entering
the eye by becoming smaller in bright light and larger
in dim light.
Directly behind the pupil is the lens, which also
provides some of the eye's focusing power.
During the reading
process, muscles in the ciliary body contract, which
changes the shape of the lens to bring near objects into
focus. Around age 40, the lens becomes rigid and the
muscles are no longer able to change its shape, so
reading glasses or bifocal lenses become necessary.
The retina is made of photosensitive cells that capture light images and translate them into electrical
impulses that travel to the brain via the optic nerve.
The macula is a specialized area in the center of the
retina that is responsible for fine detail.
There is a clear gel-like substance called vitreous inside
the eye's cavity which helps maintain the spherical
shape of the eye (not shown).
The contour of your
cornea, the power of your lens, and the length of your
eye determine how clearly you can see. If these elements are matched together perfectly, light
rays are properly focused and you can see clearly.
If these elements are not properly coordinated, then
your vision will be blurry. These
focusing (we call them “refractive”) problems are
referred to as myopia, hyperopia, astigmatism, and