Vision Glossary



Accommodation (uh-kah-muh-DAY-shun). The ability of the eye and specifically crystalline lens inside the eye to focus on near objects

Add Power. This is the amount of power you would need in a bifocal, if any. As you get older you lose the ability to focus at near. You may need added power at the bottom rim of your lenses to help you see more clearly at near with your existing eyeglass prescription. Whether you are near sighted, far sighted, or have never worn eyeglasses at all, you may need to wear a bifocal lens or reading glasses at some point in your life.

After-cataract (secondary cataract). After-cataracts are a type of cataracts that form after surgery for other eye problems, such as glaucoma. After-cataracts also can develop in people who have other health problems, such as diabetes. They are sometimes linked to steroid use

Amsler grid (AM-slur). A small grid that tests for retinal disorders, and is sometimes given to macular degeneration patients to take home in order to monitor any changes in their condition

Angle, anterior chamber angle. The area in the front of the eye where fluid from inside the eye drains out

Aphakia (ay-FAY-kee-uh). Once a patient has had a cataract removed, the eye is considered "aphakic". If an intra-ocular lens is put in, which is typical, the eye is considered "pseudo-phakic"

Aqueous (AY-kwee-us). The liquid that fills the front chamber of the eye to keep the eye round and the cornea nourished

A-scan. A measurement of the length of the eye taken before cataract surgery to properly determine the power of the lens implant

Asthenopia (as-then-OH-pee-uh). Any type of uncomfortable feeling in the eye, or eyestrain

Astigmatism (uh-STIG-muh-tiz-um). An irregular shape to the cornea causes this common refractive error that can usually be corrected with glasses or contact lenses

Axis. This is the degree the cylindrical correction sits at for optimal vision. You will only have this measurement if you have cylindrical correction.


Bifocals. Glasses that correct for blurred vision far away and up close

Binocular vision. The two eyes working together to see one image without eyestrain

Blepharitis (blef-uh-RI-tus). A common bacterial infection of the eyelids and eyelashes, requiring special hygiene measures and at times prescription medication

Blind spot. An area in the field of vision where objects cannot be seen. Everyone has a normal "physiologic" blind spot, but other blind spots from strokes, glaucoma or other diseases are not normal

B-scan. A 2 dimensional ultrasound view of the inside of the eye, useful in looking beyond a cloudy cornea or hemorrhage in the eye to determine the health of the retina.


Cataract. A clouding of the normally clear human lens inside the eye, causing vision to be blurred.

ACataract extraction. A surgical procedure done with ultrasound that removes the cloudy lens to restore vision

ACentral retinal artery. The main artery that supplies blood to the eye

Central retinal vein. The main vein that circulates used blood from the eye back to the heart

Central vision. Straight ahead vision, when you look directly at someone or at a book to read

Chalazion (kuh-LAY-zee-un). A stye on the eyelid which is the result of a blocked tear duct or infection

Choroid (KOR-oyd). The middle layer of the eyeball that provides nourishment to the retina

Color blindness. The lack of ability to distinguish colors, which can be inherited or acquired from a retinal disease

Cone. A type of retinal nerve cell that is responsible for central vision and color vision

Conjunctiva (kahn-junk-TI-vuh). The clear outer membrane covering the eye

Conjunctivitis (kun-junk-tih-VI-tis). Sometimes referred to as "pink eye", an infection of the outer layer of the eye that can be caused by a bacterial or viral infection

Convergence (con-VER-genc-es). The ability of the eyes to move in toward each other, as when one is reading or looking at a near target

Cornea (KOR-nee-uh). The clear front covering of the eye, and the first surface where light is focused onto the retina

Cross-eyes. See esotropia

Crystalline lens.The clear human lens inside the eye, that along with the cornea, focuses light onto the retina to create a clear image

Cycloplegic refraction.Measurement of the eyeglass prescription after drops are instilled in the eye to "freeze" the focusing mechanism. Often done on children to obtain an accurate assessment of the actual prescription

Cylindrical Correction.This part of the prescription is used to correct astigmatism. Astigmatism is a condition that is caused when the shape of the front of the eye is football like instead of round. Therefore, the light passing through the eye is distorted and causes certain degrees of blurriness. By adding this correction to the eyeglasses you maximize clarity. This is the second set of numbers you will find in a prescription. Usually, the "cylindrical" component is "fine tuning".


Diabetic retinopathy (ret-in-AHP-uh-thee). Hemorrhages and abnormal blood vessels seen in the retina of diabetics, especially those whose disease is not controlled well

Dilated pupil. A large pupil usually created by pharmacologic agents to allow a better look inside the eye

Diopter(D) (di-AHP-tur). A unit of measurement that describes the refractive power of a lens

Diplopia. Double vision, or seeing two or more objects when there is only one

Drusen (DRU-zin). Small yellow or white deposits in the retina frequently associated with macular degeneration

Dry eye syndrome. A lack of tears produced by the eye's lacrimal gland, thought to result from inflammation. This syndrome often leads to discomfort, specifically stinging, burning and a scratchy feeling


Ectropion (ek-TROH-pee-un). The lower eyelid can lose its elasticity, causing it to turn outward, which sometimes can result in tear drainage problems and excessive tearing

Emmetropia (em-uh-TROH-pee-uh). The refractive condition whereby light is focused perfectly on the retina, and the person sees 20/20 without any form of visual correction

Entropion (en-TROH-pee-un). The lower eyelid turns inward, often resulting in eyelashes contacting the front of the eye with resultant irritation

Esotropia (ee-soh-TROH-pee-uh). An inward turning of the eye, commonly known as "crossed eyes"

Excimer laser (EKS-ih-mur). An ultraviolet laser that removes human tissue precisely and without heat, thereby shaping the eye to reduce refractive errors such as reducing nearsightedness (LASIK or PRK)

Exotropia (eks-oh-TROH-pee-uh). An outward turning of the eye, commonly known as "wall-eye"

Extraocular muscles (eks-truh-AHK-yu-lur). The muscles that control eye movements, such as when one looks up, down or to the left or right

Eyelids. The thin membrane of skin that is designed to protect the eye and keep it from drying out


Farsightedness. See hyperopia.

Fluorescein Angiography (FLOR-uh-seen an-jee-AH-gruh-fee). A dye is injected into the vein and high speed photographs are taken to look at the blood flow in the retina, meant to detect leakage of abnormal blood vessels such as in diabetes or macular degeneration

Fovea (FOH-vee-uh). The very central part of the retina, used for fine focus distance and near vision

Fundus. The back of the eye, including the optic nerve and retina


Glaucoma (glaw-KOH-muh). A progressive disease of the optic nerve, often but not necessarily associated with high intraocular pressure, leading to slow deterioration of side (peripheral) vision. If there is a family history of glaucoma, other family members have up to a ten fold chance of developing the disease and should be checked yearly

Gonioscopy (goh-nee-AHS-koh-pee). A technique to look at the angle, the area of the eye where fluid drains out, which can be abnormal in people with glaucoma


Hyperopia (hi-pur-OH-pee-uh). Also known as far-sightedness, where distant objects are seen more clearly that print/objects up close

Hyphema (hi-FEE-muh). A hemorrhage inside the eye, often resulting from blunt trauma


IOL (intraocular lens). An artificial lens, typically made of silicone or acrylic material, that is implanted in the eye at the time of cataract surgery to replace the cloudy human lens that is removed

Iris. The colored part of the eye, which constricts or dilates depending on lighting conditions


Keratoconus (kehr-uh-toh-KOH-nus). A condition that causes the cornea to warp or bulge, leading to a large degree of astigmatism which requires treatment with either a rigid contact lens or a corneal transplant procedure

Keratometry (kehr-uh-TAH-mih-tree). A measurement of the curvature of the cornea


Lacrimal gland. The gland behind the upper eyelid that produces tears

Laser. A powerful beam of light that is used in a variety of forms of surgery to remove or vaporize tissue

LASIK (LAY-sik). Stands for "Laser Assisted In Situ Keratomileusis" which involves cutting a flap on the cornea, lifting it, and reshaping the cornea below with an excimer laser to reduce nearsighted or farsightedness, then replacing the flap

Legal blindness. Typically defined in the U.S. as visual acuity (with glasses) worse than 20/200 in the better seeing eye, or in combination with significant peripheral vision loss

Lens, crystalline lens. The lens inside the eye that, along with the cornea, bends (refracts) light onto the retina in order to create a sharp focus, allowing us to see clearly

Low vision. The optometric specialty that involves helping those who are legally blind to use their remaining vision using strong magnifiers, telescopes, and daily living aids


Macula. The very sensitive central part of the retina responsible for fine focus vision and the perception of colors

Myopia (mi-OH-pee-uh). Also known as nearsightedness. where objects up close are seen more clearly than distant objects


Nearsightedness. See myopia

Neovascularization (nee-oh-VAS-kyu-lur-ih-ZAY-shun). The formation of abnormal blood vessels, as seen in poorly controlled diabetes, which can lead to hemorrhages and retinal detachment

Nystagmus (ni-STAG-mus). Rapid involuntary eye movements that may be the result of poor vision, or a neurological condition


Ophthalmologist (ahf-thal-MAH-loh-jist). An eye doctor who specializes in the diagnosis and treatment of eye diseases and surgery of the eye

Ophthalmoscope (ahf-THAL-muh-skohp). A lighted instrument used to examine the back of the eye, specifically the optic nerve and retina, to rule out conditions such as retinal detachment, diabetes, glaucoma, etc.

Optic disc. The point where the optic nerve enters the retina; not sensitive to light

Optic nerve. The main nerve of the eye which carries visual information from the retina to the visual interpretation centers of the brain

Optician (ahp-TISH-un). A professional who specializes in making and fitting eye glasses

Optometrist (ahp-TAHM-uh-trist). An eye doctor who specializes in primary care of the eye, including correction of the visual system and the diagnosis and treatment of eye diseases

Orthoptics. Eye exercises designed to strengthen eye muscles and improve the way the eyes work together and focus


Patching. Covering an amblyopic patient's preferred eye, to improve vision in the other eye.

Perimetry (puh-RIM-ih-tree). The measurement of the peripheral or side vision, often done with an automated computerized instrument

Peripheral vision. Side vision, or the awareness of objects coming from outside the straight ahead line of sight

Phacoemulsification (fay-koh-ee-mul-sih-fih-KAY-shun). An ultrasound technique used to break up the cloudy lens (cataract) inside the eye, allowing for a smaller incision

Photophobia (foh-toh-FOH-bee-uh). Sensitivity to light or glare

Pinguecula (pin-GWEK-yu-luh). A growth on the outside of the eye, typically in the inner or outer corner, thought to be related to long term exposure to ultraviolet sunlight

Pink eye. See conjunctivitis

Presbyopia (prez-bee-OH-pee-uh). A condition that commonly develops after age 40, resulting from aging changes to the human lens and a lack of ability to focus up close requiring reading glasses

PRK (photorefractive keratectomy). Stands for Photo Refractive Keratectomy, a procedure to reduce or eliminate nearsightedness by scraping the outer layer of the cornea and using an excimer laser to shape the eye

Progressive Addition Lens (PAL). Invisible bifocals that focus light at a variety of intermediate and near distances

Proliterative retinopathy. See diabetic retinopathy

Pterygium (tur-IH-jee-um). A vascular growth on the outside of the eye, typically in the inner or outer corner, thought to be related to long term exposure to ultraviolet sunlight that can grow onto the cornea and affect vision

Ptosis (TOH-sis). A droopy upper eyelid

Pupil. The hole in the center of the iris that light is directed through onto the retina


Radial keratotomy (RK) (keh-ruh-TAH-tuh-mee). A surgical procedure, popular in the 1970's and 80's, that used eight spoke-like incisions to induce flattening of the cornea and correct nearsightedness. RK has been replaced by LASIK and PRK

Refraction. The measurement of the visual system to determine the appropriate eyeglass or contact lens prescription

Refractive error. The amount of nearsightedness, farsightedness or astigmatism that an individual has

Retina (RET-ih-nuh). The inner lining of the eye, consisting of sensitive nerve cells that receive light images and converts them to electrical impulses that are sent the brain by way of the optic nerve

Retinal detachment. A separation of the retina from the layers behind it, usually resulting from injury or seen in patients who are highly nearsighted. A retinal detachment can be surgically repaired but the amount of vision recovered depends on the extent of the detachment and how quickly it is diagnosed.

Retinoscope (RET-in-oh-skohp). An instrument used to determine the refractive error of the eye by shining a light in the eye and observing the reflected light images

Rod. A type of retinal nerve cell responsible for night vision and peripheral vision


Schlemm's canal (shlemz). The drainage channel where fluid exits the eye

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

Secondary cataract. See after-cataract

Slit lamp. Also called a biomicroscope, used to magnify structures in the front and back of the eye to examine various structures and diagnose abnormal conditions

Snellen chart. A vision chart that is read to determine one's visual acuity, or clarity of vision

Spherical Correction. This measures the amount of correction that a person needs to see clearly at near of distance. This number can stand alone as a prescription or be combined with another set of numbers to complete a prescription. This number is always the first set of numbers in the prescription.

Strabismus (struh-BIZ-mus). A misalignment of the eyes, often leading to double vision

Sty, stye. See chalazion


Tonometry (tuh-NAH-mih-tree). The measurement of the pressure inside the eye, often related to glaucoma

Trabecular meshwork (truh-BEK-yu-lur). The drainage channel in the front of the eye, and the area that is lasered in glaucoma that does not respond to medication

Trifocal (TRI-foh-kul). A segmented lens for up close, with one section for intermediate (computer) range and another for reading vision

20/20. The smallest line of the eye chart that someone with perfect vision can see


Uvea, uveal tract (YU-vee-uh). The middle layer of the eye, sandwiched between the retina and choroid, that supplies the eye with nutrients via the blood vessel system


Visual acuity. The level of clarity of vision

Visual field. The total area that can be seen both straight ahead and to the side

Vitreous (VlT-ree-us), vitreous humor. The gel like substance that fills the back chamber of the eye, helping keep the eye round

Vitreous detachment. A separation of the gel like vitreous from the retina, in some cases leading to a retinal tear or detachment

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