| DICTIONARY OF TERMS
Amsler Grid
Home eye test featuring equally spaced horizontal and vertical lines in a grid pattern. Used for determining the presence of macular degeneration and other defects that affect central vision. Back To The Top Anterior Segment
The front third of the eyeball, including the structures located between the front surface of the cornea and the vitreous. Back To The Top Aphakia
Absence of the eye’s natural crystalline lens, usually after cataract extraction. Aqueous Humor The clear watery fluid that fills the space between the corneal surface and the inner lens. This fluid nourishes the cornea, iris and lens and maintains intraocular pressure. Back To The Top Astigmatic Keratotomy (AK)
Surgical procedure used to correct moderate cases of astigmatism. Often performed at the same time as the Radial Keratotomy (RK) procedure for correcting nearsightedness. The procedures are somewhat similar, differing primarily in the pattern of incisions made in the outer periphery of the cornea in order to change its shape to the curvature needed to correct the refractive problem. Both AK and RK have been largely replaced by newer refractive surgery procedures. Back To The Top Astigmatism
Uneven curvature of the cornea in which refractive light rays are bent out of focus resulting in distorted vision. People with astigmatism are usually born with the disorder and it does not worsen with age. Often occurs in conjunction with nearsightedness or farsightedness. Back To The Top Automated Lamellar Kera lasty (ALK)
Refractive eye surgery procedure that uses an instrument known as a microkeratome to lift a flap of corneal material and to sculpt the underlying corneal tissue. Has been used successfully in correcting relatively high degrees of nearsightedness and some cases of farsightedness, but has been largely replaced by LASIK and other laser procedures that offer greater accuracy. Back To The Top Biomicroscope
Also known as a slit lamp, this precision microscope is used for examining the eye. It allows the cornea, lens and otherwise clear fluids and membranes to be examined in layer-by-layer detail. In preparation for cataract surgery, the surgeon uses this instrument to determine the condition of the cataract. Back To The Top Blind Spot
A small area of the retina where the optic nerve enters the eye, this type of blind spot occurs normally in all eyes. Also called optic disk. 2. Any gap in the visual field corresponding to an area of the retina where no visual cells are present; this type of blind spot is associated with eye disease. Back To The Top Cataract
Clouding of the natural lens of the eye, usually a process of aging or excessive exposure over the years to ultra violet sun rays, causing blurred vision. Most people over 60 years of age have some degree of cataracts. During modern cataract surgery, this natural lens is removed and replaced by an intraocular lens. Back To The Top Choroid
Layer of major blood vessels, which lies between the retina and the sclera (white of the eye), that provides oxygen and nutrients to the retina. Back To The Top Ciliary Body
A tissue surrounding the inside of the eye composed of ciliary muscle and ciliary processes that produce aqueous fluid. This muscle is also involved in lens accommodation and control of intraocular pressure. Back To The Top Cone
A type of specialized light-sensitive cell (photoreceptor) in the retina that provides sharp central vision and color vision. Highly concentrated in fovea. Three classes of cones exist: short, medium, and long wavelength cones. Back To The Top Conjunctiva
Thin, transparent membrane that lines the inner surface of the eyelid and covers the sclera where it becomes the white of the eye. Back To The Top Cornea
Clear structure that covers the front part of the eye including the iris and pupil. The cornea provides most of the eye’s optical power, while the crystalline inner lens, located behind the iris serves to “fine tune” the focus of the images. When both are working properly, a sharp image is focused on the retina and transmitted through the optic nerve to the brain. Back To The Top Diabetic Retinopathy
Potentially serious complication of diabetes that results in the weakening of tiny blood vessels that nourish the retina. These vessels may leak causing a variety of complications including the formation of scar tissue on the retina, a decrease in nourishment to the retina or blood in the vitreous humor (fluid that fills the inner cavity of the eye) causing cloudy vision. If the condition is not caught and treated during the early stages, it can result in blindness. For this reason, diabetics should have regular and frequent eye examinations. Back To The Top Drusen
Tiny yellow or white deposits in the retina of the eye or on the optic nerve head, visible to an eye care specialist during an eye examination. One of the most common early signs of age-related macular degeneration (ARMD). The presence of drusen alone does not indicate disease, but it may mean that the eye is at risk for developing more severe ARMD. Back To The Top Dry Eye
Condition due to a deficiency in the production and/or composition of tears by the eye’s lacrimal glands. Symptoms are redness, swelling and irritation, often accompanied by excessive watering of the affected eye. The condition is more common as the eye ages and may be worsened by a dry climate, exposure to wind, smoke, smog, air conditioners and ceiling fans. Most dry eye can be corrected by the use of artificial tear drops prescribed by your eye doctor. Back To The Top Flashes
Bright bursts of light that are sometimes seen when the eyes are closed. These occur normally as the eye ages and the vitreous humor, which is a jelly-like substance that fills the center cavity of the eye, begins pulling away from the retina. The flashes can appear off and on for several weeks or months. If there is a sudden appearance of many light flashes, an ophthalmologist should be consulted immediately to see if the retina has been torn. Back To The Top Floaters
Particles that float in the vitreous, which is jelly-like substance that fills center cavity of eye, and cast shadows on the retina. The particles appear to be strung together with a web-like thread. Some floaters are formed before birth while others occur normally with aging. The sudden appearance of many floaters can be an indication of a serious eye disorder and should be checked by an eye care professional. Back To The Top Fluorescein angiography
Test used to examine blood vessels in the retina, choroid and iris of the eye. Fluorescein dye that highlights the blood vessels in a patient’s eye is injected into an arm vein and rapid, sequential photographs are taken of the eye as the dye circulates. Observation of the process makes it possible for the eye doctor to determine if and where any hemorrhaging is occurring in the retina and how it might be treated with a heat-sealing laser. Back To The Top Fovea
A small rodless area of the retina that affords the sharpest vision because the layers of the retina spread aside to let light fall directly on the cones, which are the cells that give the clearest vision. Back To The Top Glaucoma
Condition caused by excessive buildup of fluid inside the eye putting pressure on the retina. The leading cause of blindness among adults in the United States. There are two types of glaucoma; the most common being open angle and the less common, but more serious, called narrow angle. Glaucoma has few if any symptoms, but a simple, painless eye test detects the problem. If untreated, glaucoma can result in gradual, painless, irreversible loss of vision. Back To The Top Hyperopia (farsightedness)
Vision that results when there is too short a distance from the cornea to the retina. This can be caused by an eye that has a vertical oval shape or a cornea that is flatter than normal. In either case, a person who is farsighted sees well at a distance but has poor reading vision. Those who are farsighted are usually born with the disorder. Back To The Top Intra-Capsular Cataract Extraction (ICCE)
Older method of cataract surgery that involves removal of the entire lens. Some surgeons may still use this method in selected cases. Back To The Top Intraocular Lens (IOL)
Prescription-engineered plastic lens surgically implanted to replace the focusing power of the natural crystalline lens following cataract extraction or during a refractive surgery procedure called Clear Lens Extraction. Back To The Top Iridectomy
A painless surgical procedure that involves removing a part of the iris to prevent blockage of the normal process whereby fluid from the aqueous humor is continually drained from the eye. This is done to prevent the build-up of unnatural pressure inside the eye that could lead to glaucoma. Back To The Top Iris
Ring of pigmented tissue lying behind the cornea that gives color to the eye and controls the amount of light entering the eye by varying the size of the pupil. Back To The Top Keratometer
Device for measuring the curvature of the cornea and for detecting and measuring astigmatism. The keratometer measures the frontal curvature, or steepness, of the cornea and compares high and low points to determine if a refractive problem exists. It is frequently used by eye surgeons to help plan a refractive eye surgery procedure. Back To The Top Laser
Acronym for Light Amplification by Simulated Emission of Radiation. A very narrow, hi-intensity light, which can vaporize tissue and/or join structures. Eye care practitioners use several types of lasers for treating various eye conditions. Back To The Top Laser In-Situ Keratomileusis (LASIK)
Currently the most widely used refractive eye surgery procedure. Combines the minimal post-operative discomfort of Automated Lamellar Kera lasty (ALK) with the computer-controlled precision of Photorefractive Keratectomy (PRK). As in ALK, a flap of corneal tissue is lifted to expose underlying tissue, which is then sculpted by the Excimer laser as in PRK. Back To The Top Laser Epithelial Keratomileusis (LASEK)
A relatively new refractive eye surgery procedure that is technically a variation of PRK (Photorefractive Keratectomy). The procedure is used mostly for people with corneas that are too thin or too flat for LASIK. Rather than cutting a flap of cornea as in LASIK, the surgeon loosens the outer surface with a diluted alcohol solution and pushes it aside. The corneal surface is than shaped with a laser, after which the flap is returned to its original position. Back To The Top Lens: Crystalline
Natural lens of the eye that lies behind the iris and helps bring light rays to focus on the retina. Muscular elastic fibers contract or expand the lens so that it can focus on objects at varying distances. In this manner, the lens fine-tunes the focus of the light rays refracted by the cornea so that a sharp, clear and colorful image is focused on the retina. The lens of the eye is often compared to the lens of a camera. Back To The Top Macula
Small centralized group of light-sensitive cones located in the central part of the retina responsible for acute central vision. Damage to this portion of the retina severely limits a patient’s ability to read, recognize faces and perform any other task that requires straight-ahead vision. Back To The Top Multi-focal
Eyeglasses or contact lenses that allow the wearer to focus through different prescriptions for different distances on the same lens. Bifocals have two points of focus, one for distance and the other for near, while trifocals have three points of focus — distance, intermediate and near. Progressive “no-line” eyeglass lenses offer a continuous range of focus from to bottom. Back To The Top Myopia (nearsightedness)
The front curvature of the cornea is too steep in a nearsighted person, causing good reading vision but poor distance vision. Back To The Top Ophthalmologist
A medical doctor (M.D.) with education, training and experience in medical and surgical treatment of eye diseases and disorders. Back To The Top Optic Disc
The circular area in the back of the inside of the eye where the optic nerve connects to the retina. Also called the optic nerve head. Contains no photoreceptors and therefore creates a blind spot in the visual field. Back To The Top Optic Nerve
Connects the eye to the brain. It carries the impulses formed by the retina, the nerve layer that lines the back of the eye and senses light and creates impulses. The brain interprets the images. Using an ophthalmoscope, the head of the optic nerve can be seen. It can be viewed as the only visible part of the brain (or extension of it). Back To The Top Optician
Technicians trained and, in some states, certified to fill lens prescriptions and contacts and to fit eyeglasses. Some specialize in contact lenses and work in optometric or medical offices, working with an optometrist or ophthalmologist to fit contact lenses. Back To The Top Optometrist
Doctors of Optometry (O.D.) are primary health care providers who examine, diagnose, treat and manage diseases and disorders of the eye and associated structures. In accordance with state law, optometrists prescribe, fit and dispense ocular medications, glasses and contact lenses. An optometrist cannot perform surgery but often works with an ophthalmologist on pre-and post-surgical care. Back To The Top Phacoemulsification
Technique for removing eye’s natural crystalline lens in cataract surgery or clear lens extraction. Procedure makes use of an ultrasonic instrument called a phaco machine, which produces vibrations at a rate of 40,000 cycles per second, thereby dissolving the lens into small fragments. Using a hand piece, the surgeon then uses the same machine to aspirate (suck out) the contents of the lens and irrigate the eye. Back To The Top Photorefractive Keratectomy (PRK)
Refractive eye surgery procedure that employs a computer-controlled Excimer laser system to sculpt by ablation (vaporize) the central corneal zone, or visual axis. By changing the shape of the patient’s cornea, the eye care surgeon can correct some cases of nearsightedness, farsightedness and astigmatism. Back To The Top Presbyopia
An age-related eye disorder that involves deterioration in the ability of the eye's natural crystalline lens to expand or contract in order to focus on close objects. Back To The Top Pupil
Black opening behind the cornea in the center of the iris that regulates the amount of light entering the inner lens of the eye. Back To The Top Radial Keratotomy (RK)
Surgical procedure where patterned surgical incisions are made in the peripheral area of the cornea. As these incisions heal, the cornea is flattened to the degree required to make the desired refractive error correction. This early refractive vision correction procedure has been largely replaced by newer, more accurate procedures such as LASIK. Back To The Top Retina
Thin membrane that covers the inside of the back two-thirds of the eye. The retina converts images into electrical impulses to be sent along the optic nerve to the brain and be converted into images that allow vision. Back To The Top Retinal Hole or Tear
With age, the retina starts to thin and weaken, especially near its attachments with the front of the eye. In addition, the jelly-like ball that fills most of the eye behind the lens, called the vitreous, changes from a firm substance to a loose fluid. When the vitreous becomes fluid, it can easily move and tug on its attachments and become detached, pulling a small bit of retina with it. When this happens, a hole or tear is left in the retina. Retinal tears can often be surgically repaired, depending on the seriousness of the problem. Back To The Top Rod
A type of specialized light-sensitive cell (photoreceptor) in the retina of the eye that provides side vision and the ability to see objects in dim light (night vision) Back To The Top Sclera
Tough outermost layer of the eye that is visible as the white of the eye. Back To The Top Snellen Eye Chart
The chart seen in every eye doctor’s office that has the big “E” at the , below which are rows of letters and numbers in decreasing size. The chart is used to test visual acuity, with a reading of 20/20 being normal. Back To The Top Trabeculectomy
A surgical procedure used to unclog the aqueous fluid drainage canal to prevent the build up of pressure inside the eye that could lead to glaucoma and possible damage to the optic nerve. The procedure is accomplished by use of a YAG or argon laser. It is painless and usually performed on an out-patient basis. Back To The Top Uvea
Colored layers of the eye including the iris, ciliary body and choroids, that contain most of the blood vessel supply. Back To The Top Vitreous
A clear, jelly-like liquid that fills the middle of the eye. Also called the vitreous humor. Back To The Top Vitreous Detachment
Separation of vitreous, which is the jelly-like substance that fills the eye behind the lens, from the retinal surface. Frequently occurs with aging, but may occur in diseases such as diabetes and severe myopia. Usually harmless, but can create retinal tears, which may in turn lead to retinal detachment. Back To The Top |
