Patient Education Glossary

Patient Resources


An ultrasound device used to measure the length of the eyeball by emitting high frequency waves that are reflected by ocular structures and converted into electrical impulses.


The ability of the eye to maintain a clear image (focus) as power is increased or objects are moved closer. This occurs when ciliary muscle contract and zonules relax resulting in the elastic-like lens to "round up" and increase its optical power. Natural loss of accommodation with increasing age is called presbyopia..

Age-Related Macular Degeneration (ARMD/AMD)

An eye condition that leads to the deterioration of the center of the retina, called the macula, leading to loss of central vision.


The human immunodeficiency virus (HIV) is a virus that causes the body’s immune system to break down, leading to illness from infections. HIV and AIDS affect the eye by making the eyes susceptible to infection.


A group of hereditary conditions that affect how the body produces or distributes pigment. People with albinism have a reduced amount or absence of pigment in their eyes, hair and skin.

Allergies, Eye Allergies

A condition when the eyes react to an irritant or allergen, making them red, itchy, tearful and swollen.

Amblyopia (Lazy Eye)

Poor vision in one or both eyes that did not develop normal sight during childhood. 

Amsler Grid

A  grid of crisscrossed lines used to detect central visual field distortions or defects, as in macular degeneration.

Angle, Anterior Chamber Angle

Junction of the back surface of the cornea and the front surface of the iris, where aqueous fluid drains or filters out of the eye.


Pupils present as different sizes.

Anterior Chamber

The fluid-filled space between the innermost layer of the cornea (endothelium) and the iris.

Aqueous, Aqueous Humor

Clear, watery fluid produced by the ciliary processes filling the space between the inner surface of the cornea and the front surface of the vitreous, bathing the lens and nourishing the cornea, iris and lens and maintaining intraocular pressure.


An imperfection in the curvature of your cornea — the clear, round dome covering the eye’s iris and pupil — or in the shape of the eye’s lens, causing refractive power not being uniform in all directions (meridians) resulting in blurry or distorted vision.  Light rays entering the eye are bent unequally at the different meridians, preventing formation of sharp focus of image on the retina.  Mild uncorrected astigmatism may not be symptomatic but moderate to severe amounts may result in significant blurring and headache.


The brand name for bevacizumab, a drug injected into the eye to slow vision loss in people who have “wet” age-related macular degeneration (AMD).

Bacterial Keratitis

Bacterial keratitis is an infection of the cornea, often due to improper care and cleaning of contact lenses or from injury to the cornea.

Bell’s Palsy

Bell's palsy is a temporary condition that causes certain muscles in your face to weaken or become paralyzed.


Eyeglasses that distinctly incorporate two different powers for distance and reading correction.  A line is usually seen in between the different powered lenses.

Black Eye

A black eye is bruising around the eye due to an injury to the face or head.


Irritation or inflammation (swelling) of the eyelids, where the upper and lower eyelids become coated with oily particles and bacteria near the base of the eyelashes. Blepharitis causes irritation, itchiness, redness, crusting, and stinging or burning of the eye.

Blocked Tear Duct

A blocked tear duct is when the eye’s drainage system for tears is either partially or completely obstructed. Tears cannot drain normally, causing a watery, irritated or chronically infected eye.

Branch Retinal Vein Occlusion (BRVO)

Branch retinal vein occlusion (BRVO) is a blockage of the small veins in the retina.


Clouding of the eye’s normally clear lens, causing vision problems.


Cellulitis is a bacterial infection of tissue that can affect both the eyes and skin.

Central Retinal Vein Occlusion (CRVO)

Central retinal vein occlusion (CRVO) is a blockage of the main vein in the retina.

Central Serous Retinopathy

In central serous retinopathy, fluid builds up under the retina and distorts vision.

Chalazia and Styes

A chalazion is a lump on the eyelid caused by enlarged oil-producing gland in the eyelid. A stye is also a lump on the eyelid, usually caused by an infected eyelash follicle.

Choroidal Neovascular Membranes

In the eye, a healthy, intact retina is key to clear vision. Choroidal neovascular membranes (CNVM) are new blood vessels that grow beneath the retina and disrupt vision. CNVM are associated with many serious eye diseases.


A coloboma describes conditions where normal tissue in or around the eye is missing from birth.

Color Blindness

Color blindness occurs when you are unable to see colors in a normal way. Most commonly, color blindness happens when someone cannot distinguish between certain colors, usually between greens and reds, and occasionally blues.

Conjunctivitis (Pink Eye)

Conjunctivitis is swelling of the conjunctiva — the thin, filmy membrane that covers the inside of your eyelids and the white part of your eye (sclera).

Contact Lens-Related Eye Infections

The most common infection related to contact lens use is keratitis, an infection of the cornea (the clear, round dome covering the eye's iris and pupil).

Corneal Abrasion

Corneal abrasion is a scratch or scrape on the eye’s cornea.

Corneal Dystrophies

Corneal dystrophies are a group of relatively rare genetic eye disorders in which abnormal material often accumulates in the cornea.

Corneal Erosion

Corneal erosion affects the cornea, the clear dome covering the front of the eye. The outermost layer of the cornea is the epithelium. When the epithelium does not stay attached correctly to the corneal tissue below, this can cause a condition called corneal erosion.

Corneal Laceration

Corneal laceration is a cut on the cornea.

Corneal pachymetry

Corneal pachymetry is the process of measuring the thickness of the cornea. It is used to perform prior to refractive surgery, for Keratoconus screening, LRI surgery and is useful in screening for patients suspected of developing glaucoma among other uses.

Corneal Topography

Corneal topography, also known as photokeratoscopy or videokeratography, is a non-invasive medical imaging technique for mapping the surface curvature of the cornea, the outer structure of the eye. The three-dimensional map is a valuable aid to the examining ophthalmologist as it can assist in the diagnosis and treatment of a number of conditions; in planning cataract surgery and intraocular lens (IOL) implantation (plano or toric IOLs); in planning refractive surgery such as LASIK, and evaluating its results; or in assessing the fit of contact lenses.

Corneal Transplant

A healthy, clear cornea is necessary for good vision. Scars, swelling or an irregular shape can cause the cornea to scatter or distort light, resulting in glare or blurry vision.

Corneal Ulcer

A corneal ulcer is an open sore on the cornea.

Cytomegalovirus Retinitis

Cytomegalovirus retinitis (CMV retinitis) is a serious viral eye infection of the retina, the light-sensing nerve layer that lines the back of the eye. It is most often found in people with compromised immune systems.

Diabetic Retinopathy

Diabetic retinopathy is a common diabetic eye disease caused by changes in retinal blood vessels.

Dilating Eyedrops

Dilating eyedrops (called mydriatics) are used to dilate, or enlarge, the pupils of your eyes so that your eye doctor can see the inside of your eye in detail.


Drusen are yellow deposits under the retina. While drusen likely do not cause age-related macular degeneration (AMD), their presence increases a person’s risk of developing AMD.

Dry Eye

Dry eye is a condition where the eyes don’t produce enough tears or the right quality of tears to be healthy or comfortable.

Endothelial Cell Count (ECC)

Specular microscopy topography is a rapid, non-invasive in-office test that that does not require any ocular anesthesia. This test can examine the size, shape and density of the corneal endothelial cells. Serial measurements can be obtained to follow the health of these cells. Any suspected abnormality of the corneal endothelium such as endothelial dystrophy, Fuchs dystrophy, pseudophakic corneal edema can be monitored with this test. 

Eye Cancer

Cancer of the eye is a malignancy that starts and grows in your eye. A malignancy is a group of cells that are cancerous and that can spread to other sites in the body or invade and destroy tissues.

Eye Lymphoma

Primary intraocular lymphoma (PIOL) involves the retina, vitreous and optic nerve. Eighty percent of cases involve both eyes; many people with PIOL will develop lymphoma within the part of the brain called the cerebrum.

Farsightedness (hyperopia)

Hyperopia (farsightedness) is a refractive error, which means the eye does not bend or refract light properly. With hyperopia, distant objects look clear but close objects appear blurred.

Floaters and Flashes

Floaters are shadows cast on the eye’s retina from clumps of gel or cells inside the vitreous. Flashes are flashes of light that you see when the vitreous gel pulls or rubs the retina.

Fuchs' Dystrophy

Fuchs’ dystrophy is a progressive eye disease affecting the cornea, causing certain cells to deteriorate and die off, making corneal cells swollen and cloudy.

Fundus Photography

A fundus camera or retinal camera is a specialized low power microscope with an attached camera designed to photograph the interior surface of the eye, including the retina, retinal vasculature, optic disc, macula, and posterior pole. It is critical to identify progressive changes in the optic nerve that may indicate damage from glaucoma. Photographs allow comparison of the optic nerve appearance over the course of time. Photographic techniques allow us to capture three-dimensional, images to better highlight glaucoma damage. 

Fungal Keratitis

Fungal keratitis is an infection of the cornea, often due to improper care and cleaning of contact lenses or from injury to the cornea.

Giant Cell Arteritis

Giant cell arteritis (GCA) is a swelling of the arteries, which are the blood vessels that carry blood away from the heart. When arteries swell, it reduces the blood flow through these vessels. GCA affects the arteries in the neck, upper body and arms. Because these blood vessels also help nourish your eyes, reduced blood flow can cause sudden, painless vision loss.


Glaucoma is a disease that damages the eye’s optic nerve.


Gonioscopy is an eye examination to look at the front part of your eye (anterior chamber) between the cornea and the iris. Gonioscopy is a painless examination to see whether the area where fluid drains out of your eye (called the drainage angle) is open or closed.

Graves' Disease

Graves disease is an autoimmune disorder that leads to over activity of the thyroid gland. The gland produces hormones that regulate your body’s metabolism. When Graves’ disease affects the eyes, the condition is known as thyroid eye disease.


Hemangioma is a non-cancerous tumor caused by abnormal growth of blood vessels. Hemangiomas can occur anywhere on the body, but are most commonly found on the face and neck. While they can be present at birth, hemangiomas more often appear during the first six months of life.

Herpes Keratitis

Herpes keratitis is a viral infection of the eye caused by the herpes simplex virus (HSV). Type I HSV is the most frequent cause of eye infections.

Herpes Zoster (Shingles)

The virus varicella zoster causes two distinct diseases: chicken pox and, if reactivated later in life, herpes zoster, more commonly called shingles.


Histoplasmosis is a disease caused when airborne fungus spores are inhaled into the lungs. Histoplasmosis initially is a lung infection. However, it is believed that the infection, even if mild, can later migrate to the eye through the blood stream and cause a serious eye disease called ocular histoplasmosis syndrome (OHS).


The human immunodeficiency virus (HIV) is a virus that causes the body’s immune system to break down, leading to illness from infections. HIV and AIDS affect the eye by making the eyes susceptible to infection.


A hyphema is a collection of blood in the front part of the eye.

Iridocorneal Endothelial Syndrome

Iridocorneal endothelial syndrome (ICE) is a rare group of conditions whose three main features include swelling of the cornea, changes in the iris, and a form of glaucoma.

Ischemic Optic Neuropathy

Ischemic optic neuropathy (ION) is a sudden loss of central vision, side vision or both due to a decreased or interrupted blood flow to the eye’s optic nerve. Some ophthalmologists may describe ischemia of the optic nerve as a stroke at the back of the eye.

Juvenile Macular Degeneration

Juvenile macular degeneration is a series of inherited eye disorders that affects children and young adults. The most common form of juvenile macular degeneration is Stargardt disease. Other types of juvenile macular degeneration include Best’s disease and juvenile retinoschisis. All of these diseases are rare and cause central vision loss.


Keratitis is a condition where the cornea becomes swollen or inflamed, making the eye red and painful and affecting vision.


Keratoconus is a condition when the normally round cornea becomes thin and develops a cone-like bulge.

Lazy Eye (Amblyopia)

Lazy eye is poor vision in an eye that did not develop normal sight during childhood. Lazy eye is also called amblyopia.

Low Vision

Low vision is a loss of eyesight that makes everyday tasks difficult or impossible, affecting central and/or peripheral (side) vision. Low vision cannot be improved with regular eyeglasses, medicine or surgery.


Lucentis is the brand name for ranibizumab, a drug injected into the eye to slow vision loss in people who have “wet” age-related macular degeneration (AMD).

Macular Degeneration

Age-related macular degeneration is an eye condition that leads to the deterioration of the center of the retina, called the macula, leading to loss of central vision.

Macular Edema

Macular edema is a swelling or thickening of the macula, the area of the retina responsible for central vision.

Macular Hole

Macular hole is a small break in the macula, the central area of the retina that is responsible for central vision.

Macular Pucker

A macular pucker is when the macula—part of the eye’s retina—wrinkles, creases or bulges, leading to blurry or distorted vision and possibly a blind spot in your visual field.

Macular Telangiectasia

Macular telangiectasia is a disease affecting the macula, causing loss of central vision. The macula is a small area in the retina that is responsible for your central vision. Macular telangiectasia develops when there are problems with the tiny blood vessels around the fovea, the center of the macula.

Marfan Syndrome

Marfan syndrome is a genetic condition that affects the body’s connective tissue. Marfan syndrome can affect many different parts of the body, including the eyes.

Microvascular Cranial Nerve Palsy

Microvascular cranial nerve palsy (MCNP) is a neurological condition that affects the muscles that move the eyes, causing inability to move the eyes in certain directions, double vision and sometimes a droopy eyelid.


Classic migraine starts with visual symptoms such as zigzag lines, colored lights or flashes of light expanding to one side of your vision over 10 to 30 minutes, followed by a single-sided pounding, severe headache. Along with the headache, you may have nausea, vomiting and light sensitivity. Common migraine may cause only a headache felt on both sides of the head.

Mohs Surgery

Mohs surgery is a procedure used to remove skin cancer. Because the surgery removes only tissue with cancer cells, it is commonly used on areas of the body where it is important to minimize the removal of healthy tissue. For the eye area, Mohs surgery is used to remove basal cell and squamous cell cancers found on the eyelids or around the eyes, and sometimes to remove melanoma.

Myasthenia Gravis

Myasthenia gravis is a chronic autoimmune disorder that causes muscles to weaken and tire easily. Most people affected by myasthenia gravis develop “ocular myasthenia” first, where the muscles that control eye and eyelid movement are affected, causing eyelid drooping, blurry vision or double vision.

Nearsightedness (Myopia)

Myopia (nearsightedness) is a refractive error, which means the eye does not bend or refract light properly. With myopia, close objects look clear but distant objects appear blurred.


A nevus (plural, nevi) in the eye is a common, benign, pigmented growth, similar to a mole on your skin.


Nystagmus is an involuntary, rapid and repetitive movement of the eyes — either side-to-side, up and down or vertical.

Ocular Hypertension

Ocular hypertension is when the pressure inside the eye (intraocular pressure) is higher than normal. Unlike glaucoma, with ocular hypertension the optic nerve appears normal and no signs of glaucoma are found during visual field testing, which tests side (peripheral) vision.

Ocular Melanoma

Ocular melanoma (also called eye melanoma) is a type of cancer that develops in the cells that produce pigment — the substance that gives your skin, hair and eyes color.


Ophthalmoscopy, also called funduscopy, is a test that allows an eye care professional to see inside the fundus of the eye and other structures using an ophthalmoscope. It is crucial in determining the health of the retina, optic disc, and vitreous humor.

Optic Neuritis

Optic neuritis is an inflammation of the eye’s optic nerve.

Optical Biometry (IOL Master)

Optical biometry is the current standard for intraocular lens (IOL) power calculations in clinical practice. The test allows for fast, accurate measurements of multiple areas of the eye, such as eye length and surface curvature, which are necessary for cataract surgery.

Optical coherence tomography (OCT)

Optical coherence tomography (OCT) is a non-invasive imaging test that uses light waves to take cross-section pictures of your retina, the light-sensitive tissue lining the back of the eye. With OCT, each of the retina's distinctive layers can be seen, allowing your ophthalmologist to map and measure their thickness.

Photokeratitis, including Snow Blindness

Photokeratitis is a painful eye condition that occurs when your eye is exposed to invisible rays of energy called ultraviolet (UV) rays, either from the sun or from a man-made source. Photokeratitis is like having a sunburned eye.

Pigment Dispersion Syndrome

Pigment dispersion syndrome is a condition in which increased amounts of pigment, the material that gives your iris its color, circulate in other parts of the eye. The tiny granules of pigment can clog your eye’s drainage system, causing eye pressure problems.

Pinguecula and Pterygium

Pinguecula and Pterygium are common, non-cancerous growths on the cornea and conjunctiva likely caused by exposure to ultraviolet (UV) light, dry eye and wind and dust.

Pink Eye (Conjunctivitis)

Pink eye (called conjunctivitis) is swelling of the conjunctiva — the thin, filmy membrane that covers the inside of your eyelids and the white part of your eye (sclera).


Presbyopia is an age-related condition when the eye’s lens doesn’t change shape as easily as it once did, making it more difficult to read or see things at close range.


Ptosis is when the upper eyelid droops, sometimes restricting or blocking vision.


A series of different powered lenses are presented to determine eye’s refractive error and best prescription that can provide sharpest, clearest or best vision.

Retinal Detachment

Separation of the retina from the underlying pigment epithelium, disrupting visual cell structure and thus markedly disturbing vision.  Commonly a result of vitreous detachment or retinal tear, and often requires immediate surgical repair.

Retinitis Pigmentosa

Retinitis pigmentosa is a group of genetic disorders that affect the retina’s ability to respond to light, causing a slow loss of vision.


Retinoblastoma is cancer of the eye that begins in the retina, and is most common among children.

Retinopathy of Prematurity

Retinopathy of prematurity (ROP) is an eye disease that occurs in a small percentage of premature babies where abnormal blood vessels grow on the retina.


Scleritis is a painful swelling of the white part of the eye, which is also known as the sclera. In almost half of all cases, scleritis is associated with an underlying autoimmune disorder such as rheumatoid arthritis. There are two main types of scleritis: anterior and posterior.

Shingles (Herpes Zoster)

The virus varicella zoster causes two distinct diseases: chicken pox and, if reactivated later in life, herpes zoster, more commonly called shingles.

Stargardt Disease

Stargardt disease is the most common form of inherited juvenile macular degeneration. The progressive vision loss associated with Stargardt disease is caused by the death of specialized, light-sensitive photoreceptor cells in the central portion of the retina called the macula.

Steroid Tablets

Corticosteroids are medications used to treat inflammatory conditions affecting the eye and other parts of the body. Corticosteroids are different from anabolic steroids, which are used sometimes by athletes and bodybuilders to enhance muscle mass. Corticosteroids are found naturally in the body and help regulate blood sugar, salt and water levels, metabolism and growth. They also help to control allergic reactions.

Stickler Syndrome

Stickler syndrome is a genetic disorder that affects collagen, the connective tissue of the body. Collagen is a main component of the cornea. People with Stickler syndrome can experience a range of problems, including eye disorders, hearing impairment and joint abnormalities.


Strabismus is a visual problem in which the eyes are not aligned properly and point in different directions. One eye may look straight ahead, while the other eye turns inward, outward, upward or downward.

Stroke Affecting the Eye

Most people know that high blood pressure and other vascular diseases pose risks to overall health, but many may not know that high blood pressure can affect vision by damaging the arteries in the eye. A stroke affecting the eye, also known as a retinal artery occlusion, is a blockage in the blood vessels in your retina.

Subconjunctival Hemorrhage

A subconjunctival hemorrhage is a single, concentrated spot of blood, or many scattered blood splotches, under the conjunctiva, a clear membrane that covers the white of the eye (called the sclera) and the inner eyelids.


Tonometry is the procedure eye care professionals perform to determine the intraocular pressure (IOP), the fluid pressure inside the eye. It is an important test in the evaluation of patients at risk from glaucoma. 

Torn or Detached Retina

A torn retina is when the retina tears in one or more places. A detached retina is when the retina is lifted off the wall of the back of the eye.


Trachoma, an eye infection affecting both eyes, is the world’s leading cause of preventable blindness. Trachoma is caused by a bacterium called Chlamydia trachomatis. If the infection is untreated, scarring occurs inside the eyelid. This leads to the eyelashes turning inward toward the eye, a condition called trachiasis. The eyelashes brush and scratch against the cornea. This continual irritation turns the cornea cloudy and can lead to the development of corneal ulcers and vision loss.


Trichiasis is a common eyelid abnormality in which the eyelashes are misdirected and grow inwards toward the eye. Those inward-turning lashes rub against the cornea, the conjunctiva and the inner surface of the eyelids, irritating the eye.

Twitching/Eyelid Spasm

Eyelid spasm or twitching, which is also called blepharospasm, is an abnormal, involuntary blinking or spasm of the eyelids.

Usher Syndrome

Usher syndrome is the most common genetic condition that affects both vision and hearing. The major symptoms of Usher syndrome are hearing loss and vision loss from an eye disorder called retinitis pigmentosa, or RP.


Uveitis is inflammation of the uvea, the middle layer of the eye between the retina and the sclera (white of the eye), and can lead to vision loss if left untreated.

Visual Acuity

Assessment of eye’s ability to distinguish object details and shape seen at a specified distance.

Visual Field Test

The purpose of visual field testing is to determine the amount of peripheral vision that may be lost. Unlike central vision, peripheral vision is insufficient to read letters or numbers and is not tested by reading a wall chart. Visual field testing most often involves presentation of a stimulus (light, a moving target, or even fingers) in the peripheral visual field while the eye is stationary. Visual field testing is subjective and requires the respondent to signal when the stimulus is identified. Sophisticated equipment using mathematical algorithms help standardize visual field testing. Peripheral vision loss occurs in many conditions besides glaucoma. Visual field testing may help separate glaucoma from non-glaucomatous causes of vision loss.  

Vitamin A Deficiency

A lack of access to a balanced diet with enough vitamin A can lead to vitamin A deficiency. Vitamin A deficiency is the leading cause of preventable blindness in children worldwide. An estimated 250,000 to 500,000 children become blind every year because of vitamin A deficiency.

YAG Laser

Laser produced in short pulses of high energy light beam to perforate, fragment or photocoagulate tissue.


Fibers behind the iris radially arranged to suspend the lens from the ciliary body and hold it in position.

Discover the AO Patient Portal Today!

Access your medical record securely from anywhere, anytime.

View & download your Health Care Summary, securely message your Physician, view appointments & visit histories, access billing statements & pay bills online, request updates to your personal information, and so much more... 

Access the AO Patient Portal

© Associate Ophthalmologists 2018. All rights reserved