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Age-related macular degeneration
(AMD) (MACK-yoo-ler dee-gen-er-RAY-shun) A leading cause of blindness in older adults. AMD gradually destroys the macula, which provides sharp, central vision needed for seeing objects clearly.
(uh-STIG-muh-tiz-um) Occurs when light is bent differently depending on where it strikes the cornea and passes through the eyeball. The cornea of a normal eye is curved like a basketball, with the same degree of roundness in all areas. An eye with astigmatism has a cornea that is curved more like a football, with some areas that are steeper or more rounded than others. This can cause images to appear blurry and stretched out.


(BREYL) The system of writing for the blind that uses characters made up of raised dots.


(KAT-uh-rakt) When the lens of the eye grows cloudy. The cloudy lens can be replaced with a plastic lens in a usually safe and successful surgery.
(KOR-nee-uh) The clear dome covering the front of your eye. It helps your eye focus light so things look sharp and clear.


(die-uh-BEE-teez) A very serious disease in which the glucose (sugar) levels in the blood are high. Diabetes can cause problems such as blindness, heart disease, kidney failure, and amputations.
Diabetic eye disease
A group of eye problems that people with diabetes may get. All of these eye problems can lead to vision loss or blindness. Diabetic eye disease includes diabetic retinopathy, cataract, and glaucoma.
Diabetic retinopathy
(die-uh-BEH-tic ret-in-AHP-uh-thee) The most common diabetic eye disease. It's caused by changes in the blood vessels of the retina. It is a leading cause of blindness in adults. Treatments that can prevent serious vision loss include medications, lasers, and/or surgery.
Dilated eye exam
(DAHY-ley-ted) Allows an eye care professional (ophthal-mologist or optometrist) to see more of the inside of the eye to check for signs of disease. During a dilated eye exam, drops are placed in the eyes to widen or dilate the pupils.


The fringe of hair edging the eyelid They close to keep particles, like dust, out of your eyes.
Protects the front of the eye. It limits light entering the eye and spreads tears over the cornea.


Farsightedness or hyperopia
(hi-pur-OH-pee-uh) A vision condition where far away objects are seen clearly, but close objects look blurred. Farsightedness happens when the light entering your eye is not focused properly because your eyeball is too short or your cornea, the clear front of your eye, isn't curved enough.
(FOH-vee-uh) The center of the macula, where your vision is sharpest.


(glaw-KOH-muh) A group of diseases that damage the optic nerve and can cause vision loss and blindness. It affects side or peripheral vision. Glaucoma can be controlled with medication, lasers, and/or surgery.


The colored part of the eye. It regulates the amount of light entering the eye through the pupil.


The clear part of the eye behind the iris that helps to focus light on the retina. It allows the eye to focus on both far and near objects.
Low vision
Even with regular glasses, contact lenses, medicine, or surgery, people find everyday tasks difficult to do. Reading the mail, shopping, cooking, seeing the TV, and writing can seem challenging.


(MACK-yoo-luh) The small, sensitive area of the retina needed for central vision. It contains the fovea.


Nearsightedness or myopia
(mi-OH-pee-uh) A common vision condition. With nearsightedness, close objects are seen clearly, but far away objects look blurred. Nearsightedness happens when the light entering your eye is not focused properly because your eyeball is too long or your cornea, the clear front of your eye, is curved too much.


(ahp-TISH-un) A trained professional who grinds, fits, and dispenses glasses by prescription from an optometrist or ophthalmologist.
(ahf-thal-MAH-loh-jist) A medical doctor who specializes in eye and vision care. Ophthalmologists are specially trained to provide the full spectrum of eye care, from prescribing glasses and contact lenses to performing complex and delicate eye surgery.
(ahp-TAHM-uh-trist) Also known as a doctor of optometry, receives different training than an ophthalmologist. Optometrists examine, diagnose, treat, and manage diseases, injuries, and disorders of the visual system, the eye, and associated structures. They also identify related systemic conditions affecting the eye.
Optic nerve
(OP-tic nurv) The bundle of more than 1 million nerve fibers that carry visual messages from the retina to the brain.


(PYOO-pul) The opening at the center of the iris. The iris adjusts the size of the pupil and controls the amount of light that can enter the eye.


(REH-tin-uh) The light-sensitive tissue lining the back of the eyeball. It sends electrical impulses through the optic nerve to the brain.


(SKLEH-ruh) The white outer coating of the eye.


Ultraviolet (UV)
(UHL-truh-VAHY-uh-lit) The sun produces radiation that we see as light. But it also produces invisible radiation called UV or ultraviolet radiation. Ultraviolet radiation may contribute to the development of eye diseases and conditions such as macular degeneration and cataract.


Vitreous humor
(VIT-ree-us HYOO-mer) The clear gel that fills the inside of the eye

Ask a Scientist: Nearsighted or Farsighted

Switch to video with audio description

Dr. Cheri Wiggs talks about what happens to our eyes when we cry and what it means to be nearsighted or farsighted.

Last updated: June 10, 2022