Eye Glossary

The removal of material from the surface of an object by vaporization, or other processes. In ophthalmology, ablation refers to the vaporization of tissue with an excimer laser used is LASIK eye surgery after the flap has been lifted.
The ability of the eye to change it's focus from distant objects to near ones. Accommodation in the eye is just like the zoom on a telescopic camera lens: the crystalline lens of the eye changes its shape to increase its focusing power. The ability of the lens to change its shape, and thus, the eye to accommodate, declines slowly with age. By about age 45 or 50, enough near focusing power is lost that reading glasses are required. This loss of accommodative ability is called presbyopia.
LEARN More about crystalens®
Accommodative Intraocular Lens
Lenses implanted in the eye after a cataract is removed which, unlike traditional intraocular lenses, allow the eye to focus on both distant and near objects and relieve the symptoms of presbyopia. Accommodative intraocular lenses include a hinge type design which enables the lens to move forward as the eye attempts to focus on near objects, and move back when distant objects are viewed. The crystalens® was the first accommodating IOL with a hinged design and the only such lens currently available in the United States.
LEARN More about crystalens®
Age-related macular degeneration (AMD)
A disease associated with aging that gradually destroys sharp, central vision. This eye disease breaks down the macula, the region of the retina responsible for the sharp, direct vision needed to perform daily tasks. Detection of this disease is difficult because visual loss is typically painless. AMD is the most common cause of vision loss in Americans age 50 and older. Evidence suggests this is more common in smokers, people with blue eyes and post-menopausal females. SEE macular degeneration
This is an abbreviation for Automated lamellar keratoplasty.
Is a rare genetic eye condition in which the iris is not present or partially absent, causing extreme light sensitivity. Aniridic patients often have poor vision as well, due to poor development of their retinas. The iris is the circular colored membrane in the middle of the eyeball. Most cases of aniridia occur in as isolated genetic defects during development. However, some cases are associated with other diseases or syndromes, such as mental retardation, genitourinary maldevelopment or kidney cancer. For more information contact: National Association for Visually Handicapped
A visual defect where the shape and size of an ocular image is different in eye to eye.
A difference in refractive power of the two eyes in which the variance is at least one diopter. If a large difference in refractive power is present between the two eyes, double vision may occur.
Anterior chamber
The space of the eyeball between the cornea and the lens which is filled with a fluid called the aqueous humor.
Aqueous humor
The fluid in the anterior chamber. This fluid helps the eye hold its shape and provides nourishment to the internal structures of the eye.
Astigmatism a rather common vision condition where the corneal or lens surface is not evenly shaped, causing one to see ghosting or shadowing of images. With astigmatism, the cornea or lens is not a perfect sphere, like a basketball, but is steeper in one direction and flatter in the other, like a football. Astigmatism is measured in terms of diopters, cylinder meridian or axis.

Aspheric lens
All man made lenses have some degree of optical imperfection, called aberrations, which degrade the quality of the image created by the lens. Aspheric lenses are designed to minimize spherical aberration, an optical aberration that results from light coming into the edge of the lens being bent more strongly than light coming through the center of the lens. Aspheric lenses are using in intraocular lenses to help provide a sharp image and highest quality of vision.
Automated lamellar keratoplasty (ALK)
Automated lamellar keratoplasty (ALK) an older form of refractive surgery used to correct vision in nearsighted patients. This type of eye surgery involves creating a thin corneal flap with a Microkeratome and then making a second, deeper cut to remove a lamellar slice of cornea. This results in a flatter, central corneal shape and less nearsightedness. This procedure is no longer regularly used as excimer laser eye surgery, such as LASIK or PRK, which provides much more accurate results.
A yellow or white appearing band around the peripheral cornea, which represents the fatty or oily deposits in the cornea. A very common and benign condition, usually seen in older patients. Arcus in a person less than 40 years of age, however, may be a sign of high cholesterol. Most commonly associated with older people of senior eyes.
Bausch & Lomb
An eye health company providing one of the most diverse eye care product portfolios. This company is well known for contact lens development and refined improvements. Their products range over the entire spectrum of wearing modalities and include such well-known brand names as PureVision®, SofLens®, Boston® and Optima®. Their products for refractive surgery include The Technolas® Excimer Laser the Zyoptix® system for customized wavefront vision correction (customized LASIK) and the Zyoptix XP and Hansatome® brands of microkeratomes.
See best corrected visual acuity.
Best corrected visual acuity (BCVA)
The best possible vision a person can achieve with corrective lenses.
Bifocal lens
Spectacle lenses used by presbyopic (LINK) patients. The top portion of the lens allows clear viewing of distance objects, while the bottom portion of the lens allows near objects to be viewed. New Intraocular Lens technology provides great promise for patients who are currently reliant on bifocals to see both near and far clearly. SEE multifocal IOL.
Binocular Vision
The blending of separate images seen by each eye into a single image, allowing images to be seen with depth perception.
Source -
A chronic inflammatory condition of the eyelids, common in children and adults, which causes redness, burning, itching, swollen and crusty lid margins and dry-eye symptoms.
Source -
Blind Spot
A small area of the retina where the optic nerve enters the eye. In this small area, no vision exists, creating a small gap in the visual field, which is normal and present in all people.
Source -
A simple, nonsurgical, treatment that can temporarily relax muscle tone, smoothing facial wrinkles and severe frown lines between the brows. Botox is a toxin that is produced by the botulism bacteria which has been pharmacologically processed to make it safe for administration by a doctor. When injected in very tiny amounts into the eyelid muscles, botox has also been found to be effective in stopping uncontrollable eyelid spasms.
Bowman's membrane
A thin, clear membrane is situated just under the surface epithelium of the cornea. This membrane is composed of strong collagen fibers and helps the cornea maintain its shape.
Broad beam laser
An older style of excimer laser which applied refractive ablation treatment to the cornea using a broad laser beam. Most excimer lasers used today utilize much smaller beams for more accurate shaping of the cornea.

The clear front wall of the eye, which works in concert with the crystalline lens to help focus light on the retina. The cornea is about the thickness of a credit card, and can be reshaped with laser refractive surgery to help correct vision.

The cornea is comprised of several layers of tissue. The surface of the cornea is covered by a very thin layer of skin cells called the epithelium, which rest on a fine collagen membrane called Bowman's membrane. The bulk of the cornea, which lies underneath the epithelium and Bowman's membrane, is called the stroma. Underneath the stroma lies Descemet's membrane. The innermost portion of the cornea is a thin layer of cells called the endothelium, which are responsible for keeping the fluid inside the eye out of the cornea.

Corticosteroids (steroids)
Medications commonly used by doctors to reduce inflammation in the eye or the rest of the body. Inflammation occurs when the body
Crystalline lens

crystallineStructure inside of the human eye which helps focus light onto the retina, much like the lens of a camera. While the crystalline lens is 2/3rds water, the remaining 1/3rd of its mass is composed of highly ordered, specialized proteins. The precise ordering of these proteins allows light to pass through, and be bent, or refracted, to a focus on the retina.

Crystalline lensThe lens is constructed of several distinct sections: at the center of the lens lies the nucleus, which begins to form during the first few of weeks development in the womb. Surrounding the nucleus is the cortex

Dilated examination
Examination of the back of the eye, including the retina and vitreous. Drops are put in the eye to dilate, or make larger, the pupil, so that this exam can be performed. A dilated exam also allows the crystalline lens to be seen more easily. The effect of the dilating drops typically wears off in 4-6 hours, though some dilating drops may last for several days.
An age related condition where the upper eyelid skin looses its elasticity and begins to sag, giving the upper eyelids a "heavy" or "tired" appearance. The sagging skin may become so excessive that it can begin to create a hooding effect over the upper part of the eye, limiting the superior visual field. The function of the eyelid is unaffected in dermatochalasis, however, and a person can still fully open their eye. This condition can be cured by a blepharoplasty, which is a surgical excision of the excess eyelid skin.
Descemets Stripping Endothelial Keratoplasty (DSEK)
A partial corneal transplant procedure in which the endothelial lining of the cornea, the corneal endothelium(link to cornea glossary definition) is removed and replaced with a small disc of endothelial cells from a donor. The replacement of the malfunctioning endothelial cells allows the cornea to once again become clear by restoring the critical endothelial cells which may have been lost due to disease. DSEK is performed through small incisions and has a relatively fast recovery period. Usually, the cornea can recover its clarity by 4 to 6 weeks after the procedure. Occasionally, however, the donor endothelial cells become dislodged from the inside of the cornea and have to be repositioned surgically or replaced entirely.
(FDA) Food and Drug Administration
The United States federal government agency that is responsible for insuring the safety of food, drugs and medical devices for the country. A drug or medical device must undergo rigorous safety and effectiveness studies before being approved by the FDA for medical use in the United States.
The specialized portion of the retina that is responsible for the center of vision. When looking directly at an object, the fovea is used to see that object clearly.
A second refractive procedure performed to correct residual refractive error left over from a previous refractive procedure. An enhancement may be required to correct residual refractive error that occurred due to either under or over healing of the eye after the first procedure or under or over correction by the initial refractive procedure. In general, enhancements are needed after about 5-10% of primary LASIK or PRK procedures.
Excimer Laser
Laser used in some forms of refractive surgery, such as Laser Assisted In-Situ Keratomeliusis (LASIK) and Photorefractive Keratectomy(PRK). The excimer laser works by vaporizing tissue, rather than burning it, and is so precise that it could be used to draw shapes on a human hair. In refractive surgery, the excimer laser is used to precisely reshape the cornea to correct a person's rctiveefra error .The excimer laser was approved by the FDA for use in laser vision correction surgery in 1995. However, the technology was used on an experimental basis and in clinical trials for almost 10 years before it's FDA approval.

A form of refractive error in which light entering the eye is not properly focused on the retina, but rather would be focused at some point behind the retina if the retina was not blocking its path. Hyperopia results from the eye either being too short or from the cornea and/or crystalline lens not bending the light coming into the eye strongly enough to focus on the retina. The resulting vision is clear when distant objects are viewed, but blurry when close objects are viewed.

A pathologic condition of the eye in which the optic nerve is damaged, initially causing loss of the peripheral vision. With time, the central vision can also be lost and total blindness can occur. Glaucoma is often related to high eye pressure and current treatment approaches are aimed at lowering the eye pressure with medications or surgery.
Intraocular lens (IOL)
Prosthetic lens implant that is placed in the eye after a cataract is removed or during refractive lens exchange surgery. These lenses are made of plastic or silicone and stay permanently in the eye after removal of the crystallinelens and the cataract clouding it. Many forms of intraocular lenses are available. Most allow for excellent distance vision, but require the use of reading glasses for near tasks, like reading or sewing. Others, called multifocal lenses and accommodating lenses, allow for both distance and near correction. Toric IOLs can also be used to help correct astigmatism.
Intraocular pressure (IOP)
The pressure inside the eye created by the constant formation of eye fluid, the aqueaous humor. The eye pressure, or IOP, is followed closely in glaucoma patients and in those suspected of having glaucoma, but not firmly diagnosed. Lowering the IOP is the mainstay of glaucoma treatment.
A colored structure in the front part of the eye which acts as a diaphragm to control the amount of light entering the eye. The iris is what gives an eye the color that people notice, such as blue, green or brown. In the center of the iris is the pupil, or small opening in the iris that actually lets light enter into the eye. The iris can shrink or expand, depending on lighting conditions, to make the pupil bigger or smaller and let appropriate amounts of light into the eye.
Myopia (nearsightedness)

A form of refractive error in which light entering the eye is not properly focused on the retina, but rather is focused at some point in front of the retina. Myopia results from the eye either being too long or from the cornea and/or crystalline lens bending the light too strongly to a focus before it reaches the retina. The resulting vision is clear when objects are held close to the eye, but blurry when distant objects are viewed.

A refractive state of the eyes in which one eye is used for viewing distant objects and the other eye is used to view near objects. Monovision is used to help restore some near vision function in individuals whose eyes are presbyopic and have lost the ability to zoom in onto objects that are close to them. Monovision can be obtained through wearing contact lenses, through laser corneal eye surgery, such as LASIK or PRK, and through intraocular lens implants. Monovision requires some adaptation on the part of the brain in order to work well. While about 85% of people can adapt to monovision correction, a small percentage of people, however, may feel off-balance with monovision corrections.
An instrument which measures the thickness of the cornea. Most pachymeters use ultrasound to make measurements of corneal thickness, though some measure corneal thickness by other optical means.
Penetrating keratoplasty(PK)
A full thickness corneal transplant. During a PK, the entire cornea is removed, much like a man-hole cover, and replaced with a complete donor cornea. The donor tissue is secured in place with many sutures which are finer than a human hair. These sutures remain in place for several months, and then are slowly removed over the course of about a year.
The process of surgically removing a cataract, using ultrasound to help break the clouded crystalline lens into small pieces. These pieces are removed by washing them into a small vacuum needle. Cataract surgery by phacoemulsification requires only very small incisions into the eye for the surgery to be performed.
The process of determining what glasses prescription is required for a person. An instrument called a phoroptor [ phoroptor picture] is placed in front of the patient and nobs are rotated to place different power lenses in front of the eye. The combination of lenses that gives the sharpest vision is recorded and is called the patient
The structure of the eye responsible for capturing light and transforming it into neural impulses that are sent to the brain. The retina is like the film in a camera, as both capture and help form a usable image from incoming light. The retina is located on the inside, back wall of the eye. It can occasionally become detached from the inside wall of the eye if the eye is injured or small holes or tears form in the retina due to pathological processes.
Refractive Error

A common abnormality of the eye in which the incoming light is not focused clearly on the retina, causing vision to be blurry. Refractive error is categorized as myopia, which is commonly called nearsightedness; hyperopia, commonly called farsightedness; and astigmatism. Refractive error can usually be corrected with glasses, contact lenses refactive surgery, which allow the light to be sharply focused on the retina , resulting in clear vision.

Refractive surgery
Surgery performed on the eye which helps correct refractive error, decreasing or eliminating the need for glasses or contact lenses in order to see clearly.
Optic nerve
Structure at the back of the eye that collects the neuron signals of the retina and transmits them to the brain for processing. The optic nerve can become damaged in glaucoma and other diseases, causing loss of vision.

The loss of the ability to focus on objects close to the eye like a camera that has lost its zoom function. Presbyopia happens to everyone, and is caused by the slow decline in accommodation as a person ages. Presbyopia first appears around age 45 or 50. An individual with presbyopia notices increasing difficulty seeing things up close, and may need to hold books or sewing farther away from their eye to see them clearly. Reading glasses restore the near vision lost due to presbyopia.

An abnormal growth of the conjunctiva of the eye onto the surface of the cornea. As the conjunctiva is not clear, light is impeded from passing through the cornea in the area where the pterygium has grown. Pterygia can also bring scar tissue onto the surface of the cornea as they grow, further impeding the passage of light and causing astigmatism to occur. Pterygia can be removed surgically and the scar tissue sanded off the cornea, usually with a fine diamond-tipped corneal sander. As pterygia can recur after surgical removal, several additional techniques are used during the surgery to help prevent the abnormal tissue from growing again.
A drooping of the eyelid caused by poor function of the tendons which open the eyelid. Ptosis can be repaired surgically by reattaching the torn eyelid tendons to the eyelid plate.
Slit lamp examination
Examination of the eye using a special microscope, called a slit lamp. A slit lamp exam allows for detailed viewing of the front of the eye, including the cornea, the iris and the lens. Your doctor can also use hand-held lenses with the slit lamp to examine the back part of the eye, including the retina and optic nerve.
Specular Microscopy
A specialized microscopic and photographic examination of the cornea that shows the number and health of the corneal endothelial cells.
Trabecular meshwork
Drainage system of the eye, located at the junction of the cornea and the iris in the front part of the eye. The eye constantly makes eye fluid, which is drained in a controlled fashion out of the eye through the trabecular meshwork drain.
An inflammation of the iris and pigmented tissues inside the eye. Uveitis can be due to infection or an abnormal immune reaction by the body. In immune-related uveitis, there often is an underlying systemic inflammatory condition, such as rheumatoid arthritis, lupus or other collagen-vascular inflammatory disease.
Visual acuity
A measure of the sharpness of vision. Visual acuity is typically measured in the United States by the Snellen, or

A jelly-like substance that fills the back part of they eye and helps it to maintain its shape. In childhood, the vitreous is fairly firm in consistency and attached to back wall of the eye along the retina and optic nerve in several places. With age, though, it becomes more liquid and detached from the back wall of the eye, resulting in the formation of floaters.


Commonly referred to as lazy eye, this is an eye disorder of coordination between the eye and the brain. When amblyopia occurs the body actually prefers one eye over the other, thus causing unequal vision. This eye condition is most commonly noticed in early childhood and is a problem that can be corrected. Successful treatment of amblyopia depends upon the severity of the problem, and how old the child is when treatment is begun. Patching, and eyedrops maybe employed as needed to improve vision. The best outcome is often achieved if treatment is started before age of five years old. Pediatric ophthalmologists can assist with treatment.

LEARN More about pediatric ophthalmologist

array(13) { ["articles/"]=> string(13) "Content2/view" ["news/"]=> string(13) "Content3/view" ["events/"]=> string(13) "Content4/view" ["classifieds/"]=> string(13) "Content5/view" ["blog/"]=> string(13) "Content6/view" ["doctors/"]=> string(13) "Content7/view" ["corporate/"]=> string(13) "Content8/view" ["tag/"]=> string(13) "Content9/view" ["eye-glossary.html"]=> string(14) "Glossary/index" ["search/search.html"]=> string(12) "Search/index" ["search/.html"]=> string(12) "Search/index" ["form.html"]=> string(10) "Form/index" [""]=> string(13) "Content1/view" }

Vance Thompson Vision

Sioux Falls, SD

Minnesota Eye Consultants

Minneapolis, MN