Glossary of Terms


amblyopia: commonly called “lazy eye”. A functional defect of the eye in which the muscles that control each eye are unbalanced, resulting in unequal vision.

accommodation:  a process of the eye, in which the lens changes the shape of the eye to switch focus between distance and near vision.

AMD:  Age-Related Macular Degeneration

Amsler grid: a tool used to detect issues within the central visual field that may result from problems in the retina or optic nerve.  It involves a white background with a black grid.  Patients view the field and note any areas where the lines are missing or distorted.

astigmatism:  a refractive error of the eye in which the cornea has a warped curvature.  This prevents the light entering the eye from meeting in a single focal point, which causes a distorted image.


bifocals:  corrective lenses that have two different focusing powers.  Generally, one portion is used for distance vision and the other for near vision.

best corrected visual acuity:  the best vision that is able to be achieved through refraction, glasses, or contact lenses.

blepharitis:  chronic inflammation of the eyelid margins resulting in redness, swelling, itching, crusty lids, and dry eye symptoms.


cataract:  a clouding of the eye’s lens that affects vision, causing a blurred or distorted image, glare or halos and/or poor night vision.

conjunctivitis: Also known as “pink eye”, an eye condition in which the clear membrane over the white part of the eye (conjuctiva) becomes inflamed resulting in redness, swelling and itching.  This condition is sometimes contagious and often caused by a virus in the eye.

cornea:  the clear front section of the eye that is responsible for the majority of its focusing power.  The cornea is curved, allowing it to refract light onto the back of the eye.

corneal abrasion: A scratch or similar injury to the smooth surface of the corneal which can result in pain, irritation and/or a decrease in visual acuity.

corneal transplant: A procedure during which a diseased or damaged cornea is removed and replaced with a healthy, donor cornea.


diabetic retinopathy:  a complication of diabetes that causes retinal changes, hemorrhaging, and the potential growth of abnormal new blood vessels.

diopters:  a unit of measure of the refractive power of a lens, equal to the power of a lens with focal distance of one meter.

drusen: Tiny, white or yellow deposits on the retina or optic nerve head, often developed after age 60.  These deposits can be an early indicator of macular degeneration.

DSAEK: Descemet’s stripping automated endothelial keratoplasty.  A type of corneal transplant that replaces the damaged or diseased innermost corneal layer, (the endothelium) with a healthy donor layer.

dry eye:  insufficient moisture of the eyes, due to insufficient tear production and/or an improper chemical composition of the tear film; more common symptoms include burning, redness, tearing, foreign body sensation and light sensitivity.


excimer laser:  A laser used during refractive surgery to reshape the cornea, thus allowing it to focus images correctly on the retina.


femtosecond laser:  A laser used during LASIK to create a “flap” in the cornea.  The femtosecond laser forces millions of tiny air bubbles in between corneal layers, gently forcing open a flap, allowing access to the underlying layers of the cornea.

floroscein angiogram: A test used to visualize the blood vessels in the retina, during which a fluorescein dye is injected into the arm, then travels to the eye.  As the dye passes through the blood vessels, it allows any defects or problems within the vessels to be visualized and recorded

fundus: The interior lining of the eye, which includes the retina, macula and optic disc. The fundus is viewed through the pupil during a dilated eye exam.


glaucoma:  A group of diseases characterized by increased pressure in the eye.  Treatment is necessary to avoid damage to the optic nerve which can result in gradual and irreversible vision loss up to total blindness.


hyperopia (farsighted):  a refractive error where the light entering the cornea focuses behind the retina.  The patient’s distance vision is clear, but near vision is blurred.


intraocular lens:  A synthetic lens that replaces the eye’s natural lens, most commonly during cataract surgery.

intraocular lens: The amount of fluid pressure in the eye.  High intraocular pressure can be a sign of glaucoma and can cause permanent damage to the eye.

iris: The tissue behind the cornea that gives the eye its color.  The iris regulates the amount of light that enters the eye by adjusting the size of the pupil.



keratoconus:  A degenerative disease of the cornea characterized by the thinning and cone-shaped bulging of the central cornea.  This hereditary condition causes astigmatism and blurred vision.


laser:  “Light Amplification by Simulated Emission of Light”  It is a concentrated beam of light which can be focused to produce intense heat. Used in medicine, low power lasers are used to cauterize wounds or cut tissue in microsurgery as well as for diagnostic purposes.

LASIK:  (Laser in situ keratomileusis) a surgical procedure aimed at correcting refractive error in the eye.  After a flap is created in the surface of the cornea, an excimer laser is used to reshape the cornea to correct nearsightedness, farsightedness and/or astigmatism.

lens: The structure of the eye that fine tunes the focus of the light rays refracted by the cornea onto the retina.


macula:  The small, central area of the retina that provides high-acuity vision.

macular degeneration:  A disease in which the tissues of the macula break down, causing hemorrhaging and/or scarring, causing a loss of sharp, central vision.  Though painless, its effects are not reversible and it is the leading cause of blindness in patients over 60.

monovision:  A type of refractive correction in which one eye is corrected for distance vision and one eye is corrected for near vision. This can be accomplished through refractive surgery or corrective lenses.

multifocal:  A lens that provides more than one area of focus, such as near vision and distance vision.  Generally used to treat presbyopia along with near- or farsightedness.

myopia:  Commonly called “nearsightedness,” myopia is a refractive error where the light entering the cornea focuses ahead of the retina.  The patient’s near vision is clear, but distance vision is blurred.



ophthalmologist:  A medical doctor specializing in the  diagnosis and treatment of diseases and disorders of the eye.

optic nerve:  A bundle of nerve fibers that carry images from the retina to the brain.

optician: A professional who uses a refraction provided by an ophthalmologist or optometrist to make or dispense corrective eyewear.

optometrist:  A licensed medical professional (doctor of optometry), who provides primary eye care services such as eye examinations, the diagnosis and treatment of certain eye conditions and the prescription of visual aids such as glasses and contact lenses.


photophobia: An extreme sensitivity to light.

posterior capsular opacity:  Also called a “secondary cataract” this is the clouding of the capsule that holds the lens implant after cataract surgery, resulting in decreased vision.

presbyopia:  The aging of the eye.  The gradual loss of near vision, caused by a decreased flexibility of the eye’s crystalline lens.  This results in the need for reading glasses for close tasks.

PRK (photorefractive keratectomy): A surgical procedure aimed at correcting refractive error in the eye.  It involves the removal of the top layer of the cornea followed by the reshaping the cornea with an excimer laser to correct nearsightedness, farsightedness and/or astigmatism.  This is an alternative to LASIK.

PAL (progressive addition lenses):  Eyeglass lenses used to correct myopia or hyperopia as well as presbyopia.  The upper portion of the lens has the distance prescription while the prescription gradually changes to the reading addition on the bottom.  Unlike bifocals, these lenses have a gradual change, so there is no line to differentiate powers.

pterygium:  A non-cancerous, raised growth in the eye, generally caused by prolonged exposure to the sun. Symptoms can range from a foreign body sensation in the eye to irregular astigmatism and blurred vision depending on the size and location of the growth.  In some cases, surgical removal is necessary.

punctual plug:  A treatment for dry eye that involves the insertion of tiny silicone plugs into the tear ducts.  These plugs block the drainage of fluid through the duct, increasing the surface moisture of the eye.

pupil: The black area in the center of the iris, which adjusts to let varying levels of light into the eye.



refraction:  A test that determines the refractive error of the eye.  This information is used to prescribe the correct power of corrective lens.

refractive error:  An error in the way that the eye focuses light generally resulting in reduced visual acuity.  Common refractive errors are myopia (nearsightedness), hyperopia (farsightedness), astigmatism (an abnormally shaped cornea) and presbyopia (a loss of near vision).  Remedies include glasses, contact lenses and refractive surgery.

retina: The tissue lining the inner surface of the eye upon which the image formed by the eye’s lens is focused.  The retina then transmits this image through nerve endings along the optic nerve to the brain.

retinal detachment:  The separation of the retina from it’s supporting layers in the back of the eye.  This is a potentially vision threatening condition that requires immediate medical attention.


strabismus: A lack of coordination between the eyes that causes misalignment.  Commonly referred to as “crossed eyes.”


toric:  A type of corrective lens or intraocular implant that treats astigmatism.

20/20 vision:  The standard for normal vision. This measurement is based on the ability to view an object that is 20 feet away.  The higher the lower number, the worse the visual acuity.


Ultraviolet radiation (UVR):  Invisible, high-energy rays from the sun.  Long-term exposure can increase your risk of cataracts, macular degeneration and pterygium.  Sunglasses with UV protection are recommended to reduce these risks.


Visual Acuity:  The ability to distinguish the shapes and details of objects.

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