Words about vision and access

These definitions are written by Open Eyes in plain language, drawing on public information from sources such as the National Eye Institute. They are for general understanding and are not medical advice. If a word describes your own eyes, ask your eye care professional what it means for you.

A

Accessibility

Designing places, products and websites so people with disabilities can use them, with or without assistive technology.

Achromatopsia

A rare inherited condition in which the cone cells do not work properly. People usually have little or no color vision, blurry sight, strong sensitivity to bright light and shaky eye movements.

Age-related macular degeneration (AMD)

A common condition in which the macula wears down with age, blurring or blanking out the center of vision while side vision stays. It comes in a slower "dry" form and a faster "wet" form. See also Dry AMD and Wet AMD.

Alt text

A short written description of an image that a screen reader reads aloud. Without it, a blind user may not know the picture is there.

Amblyopia

Reduced sight in one eye caused by the brain not fully learning to use it in childhood. Also called lazy eye.

AMD

See Age-related macular degeneration (AMD).

Angiogenesis

The growth of new blood vessels. In some eye conditions, fragile new vessels grow where they should not and leak fluid or blood.

Anti-VEGF

A group of medicines, usually given as an injection into the eye, that block VEGF to slow the growth and leaking of abnormal blood vessels. They are used for wet AMD and for swelling caused by diabetes.

Antioxidant

A substance, such as vitamin C or vitamin E, that helps protect cells from damage caused by unstable molecules called free radicals. Many foods contain antioxidants.

Apoptosis

Programmed cell death, the body's orderly way of removing a cell. In several inherited retinal diseases, light-sensing cells die this way.

AREDS and AREDS2

Two large studies by the National Eye Institute that tested vitamin and mineral combinations for age-related macular degeneration. The results showed that a specific formula can slow the disease for some people with intermediate or advanced AMD. It is not for everyone, so ask your eye doctor before taking it.

Assistive technology

Any tool, device, app or software that helps a person do something that is harder because of a disability.

Astigmatism

A common refractive error where the front of the eye is shaped slightly unevenly, so things look blurred or stretched. Glasses or contacts usually correct it.

Audio description

Spoken narration of what is happening on screen, such as actions and scenery, placed in the pauses of a show or film.

Autosomal dominant

A way a condition is inherited: one changed copy of a gene, from either parent, is enough to cause it. A parent with the condition has a 1 in 2 chance of passing the changed gene to each child.

Autosomal recessive

A way a condition is inherited: a person needs two changed copies of a gene, one from each parent. The parents usually have no symptoms themselves. They are called carriers.

Autosome

Any chromosome other than the two sex chromosomes. People normally have 22 pairs of autosomes.

B

Bardet-Biedl syndrome

A rare inherited condition that causes retinal degeneration along with other features, which can include extra fingers or toes, kidney problems, weight gain and learning differences.

Best disease

An inherited condition of the macula that usually begins in childhood or the teen years. A yellow, egg-yolk-like deposit forms in the macula, and the effect on sight varies widely from person to person.

Biologics license application (BLA)

The request a company sends to the U.S. Food and Drug Administration for permission to sell a biologic product, such as a gene therapy, after testing it in clinical trials.

Blind spot

An area of the visual field where nothing can be seen. Everyone has a small normal one in each eye where the optic nerve leaves the retina. A larger blind spot is called a scotoma. See Scotoma.

Braille

A system of raised dots, arranged in cells, that is read by touch. Each cell stands for a letter, a number, a symbol or a short word.

Braille display

A device with a row of small pins that rise and fall to show braille for the text on a screen. It connects to a phone or computer.

Bruch's membrane

A thin layer of tissue between the retinal pigment epithelium and the choroid. It acts as a filter and support layer, and waste deposits called drusen can build up near it.

C

Carrier

A person who has one changed copy of a gene that causes a recessive condition. Carriers usually have no symptoms but can pass the changed gene to their children.

Cataract

Clouding of the eye's lens that blurs sight, dulls colors and increases glare. Surgery to replace the lens is common.

Central vision

The sharp, detailed sight you use to look straight at something, to read or recognize a face.

Cerebral visual impairment (CVI)

Vision loss caused by how the brain processes what the eyes send, rather than by damage to the eye.

Choroid

The layer of blood vessels between the retina and the white of the eye. It supplies oxygen and nutrients to the outer retina.

Choroideremia

An inherited condition, mostly affecting males, in which the choroid, the retinal pigment epithelium and the light-sensing cells slowly waste away. Night vision usually goes first, followed by a narrowing of side vision.

Chromosome

A tightly coiled strand of DNA inside a cell. People normally have 23 pairs, and genes are arranged along them.

Ciliary body

A ring of tissue behind the iris. It makes the fluid at the front of the eye and holds the muscle that changes the shape of the lens so you can focus.

Clinical trial

A research study with volunteers that tests whether a treatment, device or approach is safe and whether it works. See also Clinical trial phases.

Clinical trial phases

The stages of testing. Phase 1 looks mainly at safety in a small group. Phase 2 looks at whether the treatment seems to work and at side effects. Phase 3 compares it with the usual care in a larger group.

Color vision deficiency

Difficulty telling certain colors apart, such as red and green. Often called color blindness.

Cone cells

Light-sensing cells in the retina that handle sharp detail and color in bright light.

Cone dystrophy

A group of inherited conditions in which the cone cells slowly stop working. They can cause blurred sight, loss of color vision and discomfort in bright light.

Cone-rod dystrophy

An inherited condition in which cone cells are affected first and rod cells later. Sharp central sight and color usually fade first, followed by night vision and side vision.

Congenital stationary night blindness (CSNB)

A group of inherited conditions that cause trouble seeing in dim light from birth. In most forms the problem does not get worse over time.

Contrast

The difference in brightness or color between an object and its background. Higher contrast is easier to see.

Contrast sensitivity

How well you notice small differences between light and dark. It can drop even when the letters on an eye chart look fine.

Cornea

The clear dome at the front of the eye that helps focus light.

Cortical implant

An experimental device that sends electrical signals straight to the part of the brain that handles sight, bypassing the eye. It is being tested in research studies.

CSNB

See Congenital stationary night blindness (CSNB).

D

Dark mode

A display setting with light text on a dark background. Some people with glare or light sensitivity find it more comfortable; others find it harder to read.

Diabetic retinopathy

Damage to the retina's small blood vessels caused by diabetes. It can develop without early symptoms.

Dictation

Speaking to a phone or computer so it types what you say.

Dilated eye exam

An eye exam in which drops widen the pupils so the doctor can see the retina and optic nerve clearly. Vision is blurry and light-sensitive for a few hours afterward.

DNA

The molecule in nearly every cell that holds a person's genetic instructions, written in a four-letter chemical code.

Drusen

Small yellow deposits that collect under the retina. A few small ones are common with age. Larger or more numerous ones can be an early sign of age-related macular degeneration.

Dry AMD

The most common form of age-related macular degeneration. The macula thins gradually over years. In late stages, a patch of cells can die, which is called geographic atrophy.

F

FDA

The U.S. Food and Drug Administration, the federal agency that reviews medicines and medical devices before they can be sold.

Field of vision

Everything you can see at once without moving your eyes, including the sides. Also called the visual field.

Floaters

Small specks or strings that drift across your sight. Often harmless, but a sudden shower of new floaters needs an urgent eye exam.

Fovea

A tiny pit in the center of the macula with the most densely packed cone cells. It gives the sharpest sight of anywhere in the eye.

G

Gene

A section of DNA that holds the instructions for making one protein or other molecule the body needs.

Gene therapy

A treatment that delivers a working copy of a gene, or otherwise changes how a gene works, to treat a disease. One gene therapy for a form of inherited retinal disease caused by changes in the RPE65 gene has been approved by the FDA. Many others are being studied.

Genetic counselor

A trained professional who explains genetic test results and what they may mean for you and your family. Many genetic counselors work with eye clinics or can be found through a doctor's referral.

Genetic testing

A lab test, usually on blood or saliva, that looks for changes in genes. For inherited retinal disease it can confirm a diagnosis, show how the condition is passed on and help in finding clinical trials.

Genotype

A person's particular set of gene variants. It is different from the phenotype, which is how a condition actually shows up. See Phenotype.

Geographic atrophy

A late stage of dry AMD in which a patch of retinal cells has died, leaving a blind spot in or near the center of vision that can slowly grow.

Glare

Bright light that causes discomfort or makes it harder to see, such as sunlight on a wet road or an overhead lamp.

Glaucoma

A group of conditions that damage the optic nerve, often starting with the loss of side vision. Early treatment can slow it.

Guide dog

A dog trained to lead a person who is blind or has low vision around obstacles and through traffic.

Gyrate atrophy

A rare inherited metabolic condition that causes patchy loss of the retina and choroid. It often starts with nearsightedness and trouble seeing at night.

I

Inherited retinal disease

A condition passed down in families that causes the retina to work less well over time. Retinitis pigmentosa and Stargardt disease are examples.

Investigational new drug (IND) application

The filing a company or researcher sends to the FDA to get permission to test an experimental medicine in people.

Iris

The colored ring of muscle around the pupil that controls how much light enters the eye.

J

JAWS

A paid screen reader for Windows computers.

K

Keyboard navigation

Moving around a website or program using only the keyboard, with Tab, Enter and the arrow keys. Many people who cannot use a mouse rely on it.

L

LCA

See Leber congenital amaurosis (LCA).

Leber congenital amaurosis (LCA)

A group of inherited retinal conditions that cause severe sight loss from birth or early infancy. Many different genes can be the cause, and one form, caused by the RPE65 gene, can be treated with an approved gene therapy.

Legal blindness

A definition used in the United States for benefits and programs: best-corrected central sight of 20/200 or worse in the better eye, or a field of vision of 20 degrees or less. Many legally blind people still have some usable sight.

Lens

The clear part inside the eye, behind the iris, that fine-tunes focus.

Locus

The specific place on a chromosome where a gene sits. The plural is loci.

Low vision

Reduced sight that glasses, contacts, medicine or surgery cannot fully correct, and that makes daily tasks harder.

Low vision evaluation

An exam that looks at how you use your remaining sight and recommends tools, lighting and training.

Lutein and zeaxanthin

Yellow plant pigments found in leafy greens, corn and egg yolks. They collect in the macula and are part of the AREDS2 formula. See AREDS and AREDS2.

M

Macula

The small center of the retina that gives sharp, detailed central sight.

Macular edema

Swelling in the macula caused by fluid leaking from nearby blood vessels. It can follow diabetes, blocked veins in the eye or other conditions, and it blurs central vision.

Magnifier

A tool that enlarges what you look at. It can be a hand-held lens, a stand, a video device or an app.

Mutation

A change in the DNA code of a gene. Many are harmless, and some cause disease. Doctors increasingly call a change that has been tested a variant.

N

Narrator

The screen reader built into Windows.

NEI

The National Eye Institute, part of the U.S. National Institutes of Health. It supports eye research and publishes free information on eye conditions.

New drug application (NDA)

The request a company sends to the FDA for permission to sell a new medicine after clinical trials show it is safe and effective.

Night blindness

Trouble seeing in dim light or at night. It can be an early sign of some retinal conditions.

NVDA

A free, open-source screen reader for Windows computers.

Nystagmus

Involuntary, repeated movement of the eyes that can make it hard to hold a steady picture.

O

Occupational therapist

A health professional who helps people adapt everyday tasks, such as cooking or using a computer. Some specialize in vision.

Omega-3 fatty acids

Healthy fats found in fish, walnuts and flaxseed. One type, DHA, is plentiful in the retina. Studies of omega-3 supplements for eye conditions have had mixed results, so ask your doctor.

Ophthalmologist

A medical doctor who specializes in eye care and can treat eye disease and perform eye surgery.

Optic nerve

The bundle of fibers that carries visual signals from the eye to the brain.

Optical character recognition (OCR)

Software that turns a picture of printed text into text a computer can read aloud or enlarge.

Optogenetics

An experimental approach that uses gene therapy to make surviving cells in the retina sensitive to light, so that some sight might return. It is being studied in early trials.

Optometrist

An eye care professional who tests vision, prescribes glasses and contact lenses and diagnoses many eye conditions.

Orientation and mobility (O&M)

Training in knowing where you are and moving safely, often with a cane, taught by a certified specialist.

Oxidative stress

Damage that builds up when harmful reactive molecules outpace the body's ability to neutralize them. It is thought to play a part in aging and in some eye diseases.

P

Peripheral vision

Side vision: what you notice at the edges while looking straight ahead.

Phenotype

How a condition shows up in a person, such as the symptoms and the age they began. Two people with the same gene change can have different phenotypes.

Photophobia

Discomfort or pain from bright light.

Photoreceptor

A light-sensing cell in the retina. The two kinds are rod cells and cone cells.

Phototransduction

The chain of chemical steps in rod and cone cells that turns light into an electrical signal the brain can read.

Presbyopia

The normal, age-related loss of close-up focusing that usually begins in the 40s. Reading glasses help.

Pupil

The dark opening in the center of the eye. It widens and narrows to let in more or less light.

R

Refractive error

A focusing problem, such as nearsightedness, farsightedness, astigmatism or presbyopia, that glasses or contacts can usually correct.

Retina

The light-sensitive layer at the back of the eye that turns light into signals for the brain.

Retinal detachment

The retina pulls away from the back of the eye. It is an emergency that needs care right away.

Retinal pigment epithelium (RPE)

A layer of cells just behind the light-sensing cells. It feeds them, clears away their waste and absorbs stray light. When it fails, the cells it supports often fail too.

Retinal prosthesis

An implanted device, often paired with a camera worn on glasses, that sends electrical signals to the remaining cells in the retina. It is meant for some people with advanced vision loss from inherited retinal disease. Availability has changed over the years, so ask a retina specialist what is current.

Retinitis pigmentosa (RP)

A group of inherited conditions in which the retina slowly loses cells, often starting with night vision and side vision.

Retinoschisis, X-linked

An inherited condition, mostly affecting males, in which layers of the retina split apart. It reduces central sight, often from childhood.

Rhodopsin

The light-sensitive protein in rod cells. Changes in the gene for rhodopsin are one cause of retinitis pigmentosa.

RNA and messenger RNA (mRNA)

RNA is a chemical cousin of DNA. Messenger RNA carries a copy of a gene's instructions to the part of the cell that builds proteins.

Rod cells

Light-sensing cells in the retina that work in dim light and detect movement, mostly around the edges.

RPE

See Retinal pigment epithelium (RPE).

S

Sclera

The tough white outer wall of the eye.

Scotoma

A blind spot, or a patch of missing or dim sight, in the field of vision.

Screen magnifier

Software that enlarges part or all of a computer or phone screen.

Screen reader

Software that reads out what is on a screen and lets you control the device by keyboard, touch gestures or voice.

Snellen chart

The familiar eye chart with rows of letters that get smaller. It is used to measure visual acuity, such as 20/20.

Stargardt disease

An inherited condition of the macula that often begins in childhood or young adulthood and blurs central sight.

Stem cell

A cell that can divide and become other kinds of cells. Researchers are studying whether stem cells can replace damaged retinal cells. Be cautious about clinics that sell stem cell treatments for eye conditions outside of regulated trials, because these can cause serious harm.

Strabismus

A misalignment of the eyes, where one eye turns in, out, up or down. In children it can lead to amblyopia if it is not treated.

T

TalkBack

The screen reader built into Android phones and tablets.

Text-to-speech

Technology that reads written text aloud in a computer-made voice.

Tunnel vision

Loss of side vision so that only a small central area remains, like looking through a tube.

U

Ultraviolet (UV) light

An invisible part of sunlight that can damage the eyes over time. Sunglasses labeled as blocking UV protect the eyes.

Usher syndrome

An inherited condition that causes both hearing loss and vision loss.

Uveitis

Inflammation inside the eye, in the middle layer that includes the iris, ciliary body and choroid. It can cause pain, redness, floaters and loss of sight, and it needs prompt medical care.

V

Vector

In gene therapy, the carrier used to deliver a gene into cells. It is often a harmless, modified virus.

VEGF

Vascular endothelial growth factor, a protein that tells the body to grow new blood vessels. Too much of it in the eye drives abnormal vessel growth. See Anti-VEGF.

Vision rehabilitation

Training and services that help people with vision loss keep their independence, including skills, tools and counseling.

Visual acuity

How sharp your sight is, usually measured with an eye chart. Twenty-twenty (20/20) is the usual standard for normal acuity.

Visual cycle

The chain of chemical reactions in the retina that resets the light-sensing molecule in rod and cone cells so they can respond to light again and again.

Visual field

See Field of vision.

Vitreous

The clear jelly that fills the large space inside the eye.

Voice assistant

A feature that responds to spoken commands to do things like make a call, set a timer or open an app.

VoiceOver

The screen reader built into iPhones, iPads and Mac computers.

W

Wet AMD

The faster-moving form of age-related macular degeneration, in which abnormal blood vessels grow under the macula and leak. Early treatment with anti-VEGF injections can slow sight loss, so any sudden change in central vision should be checked promptly by an eye doctor.

White cane

A long cane that people who are blind or have low vision use to detect obstacles and signal to others.

X

X-linked

A way a condition is inherited: the gene sits on the X chromosome. Males, who have one X, are affected more often, and females can be carriers.

Z

Zoom (screen magnification)

A built-in setting on phones and computers that enlarges what is on the screen.