The eyes are complex organs,
with many parts that must work together to produce clear vision. Here is a
basic overview of eye anatomy.
The cornea is a layer of
clear tissue at the front of the eye that helps focus light.
Located at the corner of
each eye, tear ducts drain tears secreted by the lacrimal gland to the surface
of the eye. Tears keep the cornea lubricated and clear of debris.
Iris and Pupil
The colored part of the eye
is the iris. It is a muscle that controls the pupil, the opening in the middle
of the eye that controls the amount of light coming in.
Lens and Retina
The lens is behind the pupil and focuses light onto
the retina, the light-sensitive cells on the back of the eyeball. Acting much
like the film in a camera, the retina converts images into electrical signals
that are sent to the optic nerve.
The optic nerve is a thick bundle of nerve fibers
attached to the back of the eye that transmits visual information from the
retina to the brain.
When Things Go Wrong
Problems or malfunctions in any of eye parts cause
many common eye conditions.
When light is not focused properly, it causes
blurry vision. Refractive errors can usually be corrected with glasses,
contacts, or surgery. They include:
- myopia (nearsightedness), which is when far-away
objects look blurry
- hyperopia (farsightedness), which is when close-up
objects look blurry
- astigmatism, which can result in blurry vision
because the cornea is not perfectly shaped to direct light into the eye
- presbyopia, which is farsightedness caused by the
loss of elasticity of the eye’s lens due to aging
Glaucoma is increased pressure of the fluid inside
the eye, which can cause optic nerve damage. Glaucoma is a common cause of blindness,
particularly in diabetic patients.
Cataract is a clouding of the lens, causing blurry
or color-tinted vision. People with cataracts often report “haloes” surrounding
objects that they are looking at, particularly at night. It is most common in
older people, and cataracts can be removed by surgery that replaces the lens
with an artificial lens.
Age-related macular degeneration (AMD) is gradual
damage to the cells of the macula. This condition is most common in people over
60 years old. It causes blurry vision, especially in the center of the field of
view. According to the Foundation
Fighting Blindness, AMD is the leading cause of blindness among people over age 55 in the
Commonly referred to a "lazy eye,"
amblyopia occurs when one eye has worse vision than the other, and the brain
begins to favor the better eye. This will occur if one of the eyes is blocked
from producing clear images during the critical years from ages 0 to 6. One eye
may be inhibited by problems such as a lid droop, tumor, or crossed eyes
(strabismus) that are not fixed when a child is young. It is crucial to have
young children evaluated by an eye doctor in order to ensure that subtle signs
of amblyopia are not present.
Diabetic retinopathy is damage to the blood vessels
of the retina caused by diabetes. It causes blurred or dark spots in the field
of vision and will eventually lead to blindness. The best way to avoid these
vision problems is to keep your blood sugars under control and see your eye
doctor every year for a dilated eye exam.
Detachment or Tear
A tear in or detachment of the retina causes blurry
vision or partial loss of vision.
Dry Eye Syndrome
Dry eye is a lack of proper tears, usually due to a
problem with the tear ducts or eyelids, or a problem with certain medications.
This condition can cause pain and blurry vision.