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
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 United States.
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.
Retinal 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.