Eye Health Glossary

20/20 vision Normal visual acuity. 20/20 vision is characterized by the correct perception of an object or letter, of prescribed size, from a distance of 20 feet. aberration An irregularity or departure from the norm. In this context, an imperfection in the eye affecting vision. accommodate Way by which the eye's lens alters its focal point to bring near and far objects into focus. age-related macular degeneration (AMD) The leading cause of vision loss and legal blindness in adults over age 60, AMD affects the sharp, straight-forward vision necessary for reading, driving and other daily activities. It is an eye disease that impacts the macula, the centermost part of the retina responsible for seeing fine detail, and occurs in two forms — dry AMD and wet AMD, with wet AMD being the more serious form. allergen A substance causing the immune system to react abnormally. Common allergens are grass, tree and weed pollens, pet dander and dust. For individuals sensitive to these substances, allergens can cause mast cells in the eyes to release histamine and other chemicals, resulting in eye allergy symptoms. Amsler grid A checkerboard-patterned grid with a centrally located black dot and straight lines. This grid is often used to diagnose central vision loss - a primary symptom of age-related macular degeneration (AMD). anti-VEGF therapy An injection of drugs into the eye to help slow the growth of abnormal blood vessels in the macula. Anti-VEGF therapy is a treatment for age-related macular degeneration (AMD). apodized diffractive technology Technology similar to that used in telescopes and microscopes. Apodized diffractive technology is used to create Alcon’s AcrySof® RESTOR® IOL (Intraocular Lens) – multifocal lenses offering cataract patients a full range of quality vision, thereby decreasing dependency on glasses or contact lenses following cataract surgery. aqueous humor Clear, watery fluid filling the front part of the eye between the cornea and lens. astigmatism A common refractive condition caused by either an irregularity in the curvature of the cornea (corneal astigmatism) or the lens (lenticular astigmatism). People with astigmatism generally have difficulty seeing fine detail at all distances. This vision disorder is treated with corrective lenses or refractive surgery. bacterial conjunctivitis An eye infection commonly known as pink eye; caused by bacteria. blepharitis Chronic inflammation of the eyelid due to infection. Commonly caused by bacteria, blepharitis results in a burning sensation, increased tearing, itching, sensitivity to light, red, swollen eyelids and the sensation that something is in the eye. While blepharitis can normally be treated with a self-care regimen focusing on keeping the eyelids clean, prescription antibiotics or steroid eye drops may be used in severe cases. carbonic anhydrase inhibitor A systemic or topical drug that decreases aqueous production and secretion (of the eye). Used often in treating glaucoma. cataract A clouding of the eye's lens that blocks passage of light to the retina, resulting in impaired vision. Often a result of normal aging, cataracts form when protein clumps cloud areas of the eye's lens. As the cataract progresses, vision worsens and often requires surgical replacement of the damaged lens with an artificial one. cataracts A clouding of the lens of both eyes, blocking the passage of light to the retinas and impairing vision. Often a result of normal aging, cataracts form when protein clumps cloud areas of the eyes’ lens. As the cataracts progress, vision worsens and often requires surgical replacement of the damaged lens with an artificial one. chalazions A chalazion is an inflamed lump in the meibomian gland (in the eyelid). Inflammation usually subsides on its own, but may require surgical removal. choroid The underlying layer of blood vessels in the eye that nourish the retina. choroids Vascular layers of the eye lying between the retina and sclera that provide nourishment to outer layers of the retina. Choroids form part of the uvea, along with the ciliary body and iris. ciliary body Circumferential tissue inside the eye composed of the ciliary muscle (involved in lens accommodation and control of intraocular pressure) and 70 ciliary processes that produce aqueous. collagen The principal protein of the skin, tendons, cartilage, bone and connective tissue. coma A higher order aberration which makes items appear to have a comet-shaped "tail", creating blurring in your vision. compounds Distinct substances formed by the chemical union of two or more ingredients in definite proportion by weight. cones Light-sensitive cells in the retina, particularly the macula, that are cone shaped. Cone function performs best in daylight with a small pupil allowing the eye to distinguish details, shapes and colors. conjunctiva The tissue lining the inside of the eyelids. conjunctivitis An inflammation of the tissue lining the inside of the eyelid. Conjunctivitis, also referred to as "pink eye," is a very common and treatable eye infection. Symptoms include redness of the inner eyelid or white of the eye, increased tear flow, yellow eye discharge and itchy, burning eyes. Highly contagious, conjunctivitis is typically treated with prescription antibiotics dispensed in eye-drop form. cornea The clear, curved surface at the front of the eye through which light enters the eye. corneal epithelium The outermost layer of the cornea between Bowman's membrane and the tear film. corneal flap A thin slice of tissue on the surface of the cornea made with a microkeratome at the beginning of a LASIK procedure. This flap is folded back before the laser is applied to the inner layers of the cornea. corneal surface The outermost surface of the cornea which is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. corticosteroids Steroid eye medications used to treat chronic or severe eye allergies. diabetic retinopathy (DR) A complication of diabetes, DR compromises vision and can lead to blindness. Tiny blood vessels in the retina are weakened and leak blood and fluid into the eye, which can progress to new, abnormal blood vessel growth on the retinal surface, further affecting vision. Between 40 and 45 percent of American adults with diabetes have some form of diabetic retinopathy. dilated Widening of the pupils achieved by placing drops in the eyes. Your vision will normally be blurry for up to several hours after dilation. dilated eye exam A common examination using a magnifying lens to assess the health of the eye's retina and optic nerve. dilating When eyes are dilated, the pupils are wider than normal. This is accomplished by placing drops in your eyes. Your vision will normally be blurry for up to several hours after dilation. diopters A unit of measurement for myopia, hyperopia and astigmatism that usually falls within a scale of +14 to -14. A positive number indicates hyperopia and a negative number indicates myopia. Positive and negative numbers are also used to indicate astigmatism. Whether the number is positive or negative, the higher the number the greater the extent of the vision problem. drusen Yellowish spots under the retina common in people over age 60. Individuals with drusen in increasing size or number may be at greater risk of developing age-related macular degeneration (AMD). dry AMD A breakdown of the macula's light-sensitive cells causing blurred central vision in one or both eyes. The more common of two forms of age-related macular degeneration (AMD), dry AMD can be a precursor to the more serious – and damaging – form of the disease, wet AMD. dry eye A general term used to describe a group of conditions caused by a dry cornea. Dry eye, or keratoconjunctivitis sicca, is characterized by the depletion of tear film due to aging, medications or exposure to air pollution or other environmental factors. Common symptoms of dry eye are dry, irritated and red eyes. edema The swelling of (eye) tissues from excess fluid accumulation. episcleritis Inflammation of the episclera, or the outermost layer of the sclera (anterior or posterior). The affected eye is painful and light sensitive (photophobic). In chronic form purple nodules may develop, surrounded by localized swelling and redness. epithelium The protective layer of cells covering the cornea. excimer laser A type of laser used in laser vision correction that removes tissue from the cornea. exudative A condition that results in the leaking of protein or fatty fluid from blood vessels into retinal tissue. Usually used in reference to the "wet" form of macular degeneration. farsightedness The common term for hyperopia, a refractive error resulting in inability to see objects at close range. Farsightedness is caused by either a cornea with too little curvature or an eyeball that is too short. Both structural defects cause light entering the eye to focus incorrectly on the retina, resulting in blurred close-up vision. Eyeglasses, contact lenses and refractive surgery are treatment options for correcting farsightedness. FDA An acronym for the Food and Drug Administration, a federal agency within the U.S. Department of Health and Human Services responsible for determining the validity and safety of any drug, cosmetic, or medical device. floaters Small, shadowy "cobwebs" or specks that float around in the visual field. More likely to develop with age or in people who are very nearsighted, floaters are little more than an annoyance for most. A sudden increase in the number of floaters, or floaters accompanied by flashes of light or loss of peripheral (side) vision could indicate a more serious condition, such as a retinal detachment or diabetic retinopathy. fluorescein angiography An eye exam using an orange-colored, fluorescent dye (fluroescein) and a special camera to analyze blood circulation in the retina and choroid. fovea The area of clearest vision on the retina; a very small spot in the macula. glaucoma An eye disease that develops when too much pressure inside the eye damages the optic nerve due to the slow drainage of eye fluid through the eye's trabecular meshwork. Without treatment, glaucoma can cause permanent blindness within just a few years. Symptoms include halos around lights, tunnel vision and vision loss. Glaucoma is most often treated with medications designed to reduce intraocular pressure. halo A circular flare or hazy ring that may appear around a headlight or other lighted object. halos A visual effect, in which a circular flare or hazy ring of light may appear around a headlight or other lighted object. higher order aberrations Imperfections in the eye's optical system that may affect vision clarity and sight in low light or at night. Some eye experts believe higher order aberrations contribute to common low-light vision problems, including glare and halos. hyperopia The medical term for "farsightedness," a refractive error resulting in an inability to see objects at close range. Typically caused by either a cornea with too little curvature or an eyeball that is too short, causing light entering the eye to focus improperly on the retina and resulting in blurry close-up vision. Eyeglasses, contact lenses and refractive surgery are treatment options for correcting vision impairment caused by hyperopia. intraocular lens (IOL) An artificial lens that replaces a human lens damaged by cataracts. intraocular lens replacement Procedure whereby artificial lenses made of plastic, silicone or acrylic are implanted in the eye to improve its focus and correct vision problems associated with cataracts. intraocular lenses (IOLs) Artificial lenses made of plastic, silicone, or acrylic which are implanted in the eye to improve its focus and correct vision problems. intraocular pressure (IOP) The pressure inside the eye produced by the fluids contained within the eye. iris The membrane in front of the eye's lens that manipulates the size of the pupil, thus regulating the amount of light entering the eye. ischemic Having an abnormal reduction of retinal blood supply from varying degrees of blood vessel blockage. May result in retinal edema, cotton-wool spots, microaneurisms, venous engorgement and neovascularization. keratoconjunctivitis sicca The medical term for a common condition known as "dry eye." Dry eye occurs when the eye's tear film is depleted due to aging, medications, or exposure to air pollution or other environmental factors. Dry, irritated and red eyes are the most common symptoms. keratoconus A disease of the cornea that causes a cone-shaped protrusion of the center of the cornea. keratome A special cutting laser used in LASIK surgery to create a thin, circular-hinged cut in the cornea. After lifting the corneal flap made by the keratome's cut, an eye surgeon uses a second laser to reshape the cornea – the end result of vision-correcting LASIK surgery. keratometer An instrument measuring reflected light from the cornea. A keratometer can be used to quantify the amount of astigmatism or to determine the orientation of corneal astigmatism. keratoscope An instrument used to assess the severity of astigmatism. A keratoscope projects light rings on the cornea. Astigmatism can be evaluated by analyzing the shape and spacing of the rings through the scope. LASEK An acronym for Laser Assisted sub-Epithelial Keratectomy, a refractive surgical procedure similar to PRK, where the surface cells (epithelium) of the cornea are removed prior to laser treatment. Then the laser reshapes the cornea to improve vision. Once the laser ablation is completed, the surface cells are replaced over the reshaped area. laser trabeculoplasty A procedure to stretch the drainage holes in the eye's trabecular meshwork to improve the drainage of normal eye fluid. Laser trabeculoplasty, a treatment for glaucoma, is accomplished with a high-intensity laser and a special lens. laser-assisted in situ keratomileusis (LASIK) A type of refractive surgery that changes the shape of the cornea to correct vision disorders such as myopia, hyperopia and astigmatism. The surgery involves making a thin circular-hinged cut in the cornea using a special cutting laser called a keratome. After lifting the circular flap, an excimer laser – a laser that doesn't produce heat – is used to reshape the cornea based on the patient's corrective lens prescription. LASIK An acronym for Laser In-Situ Keratomileusis. LASIK is a type of laser surgery in which the cornea is reshaped to improve vision. A device called a microkeratome is used to surgically create a thin, hinged flap of corneal tissue. The flap is folded back, the laser is directed to the corneal surface exposed beneath the flap and the flap is brought back into place. lens The transparent disc behind the pupil that brings light into focus on the retina. lower order aberrations A collective term for a series of common vision problems including myopia, hyperopia and astigmatism. macula The center-most portion of the retina responsible for central vision and the seeing of fine detail. macular degeneration A group of conditions that include deterioration of the macula, resulting in a loss of sharp central vision. Hereditary types can occur at any age while age-related macular degeneration is the most common cause of decreased vision after age 50. microkeratome A surgical instrument used to cut a flap of corneal tissue as the first step in the LASIK procedure. middle ear infections Infections that occur behind the eardrum in the middle part of the ear, middle ear infections mainly affect children. The medical term for middle ear infection is otitis media, and usually occurs in one of three forms: acute otitis media, a sudden and temporary infection; recurrent acute otitis media, a repetitive ear infection; or chronic otitis media with effusion, a persistent accumulation of sticky, thick fluid in the middle ear. mixed astigmatism A type of astigmatism that results in blurred distance and near vision. Light rays entering the eye are bent at different points, with one point focused in front of the retina and the other point focused behind the retina. Clear vision requires that all focus points be directly on the retina. monovision Vision correction that eliminates the need for bifocals or reading glasses by correcting one eye for distance and the other for up-close vision. myopia A refractive error resulting in the inability for the eye to see distant objects. Also referred to as "nearsightedness." Occurs when the eyeball is too long or when the cornea has too much curvature, preventing the light entering the eye from focusing correctly on the retina and resulting in blurry vision at a distance. Eyeglasses, contact lenses and refractive surgery are treatment options for correcting vision impairment caused by myopia. nearsightedness The common term for myopia. Nearsightedness is a refractive error resulting in the inability for the eye to see distant objects. Occurring when the eyeball is too long or when the cornea has too much curvature, preventing the light entering the eye from focusing correctly on the retina and resulting in blurry vision at a distance. Eyeglasses, contact lenses and refractive surgery are treatment options for nearsightedness. non-steroidal anti-inflammatory drugs (NSAIDs) Nonsteroidal eye medication used to treat eye allergies. nonexudative A condition that does not result in the leaking of protein or fatty fluid from blood vessels into retinal tissue. Usually used in reference to the "dry" form of macular degeneration. nonproliferative retinopathy The earliest stage of diabetic retinopathy characterized by small areas of balloon-like swelling in the blood vessels of the retina. It is possible to have nonproliferative retinopathy with no noticeable symptoms. Symptoms of more progressive forms of the disease include blurred, distorted vision, the presence of "floaters" in the visual field and eye pain. nutraceuticals Foodstuffs (as a fortified food or dietary supplement) that provide health benefits in addition to basic nutritional value. ocular Having to do with the eye. open-angle glaucoma A potentially blinding condition that develops when too much pressure inside the eye damages the optic nerve due to the slow drainage of eye fluid through the eye's trabecular meshwork. Common symptoms include tunnel vision, halos around lights and vision loss. Open-angle glaucoma is generally treated with medications formulated to reduce intraocular pressure. ophthalmic Pertaining to the eye. ophthalmologist A physician (doctor of medicine or doctor of osteopathy) qualified to diagnose, manage and treat all eye and visual system disorders. An ophthalmologist is trained to render total eye care, including vision services, contact lenses, eye examinations, medical eye care and surgical eye care. ophthalmology Pertaining to the eye, its function, and diseases. optic nerve A bundle of nerve cells and fibers beginning in the retina that carries messages to the brain, resulting in visual images, or eyesight. optometrist An eye health professional trained to provide primary eye care services, such as eye health and vision examinations, diagnosis of vision problems and eye diseases, and prescribing of eyeglasses, contact lenses and medications. pachymetry A test using ultrasound waves to measure the thickness of the cornea. Pachymetry is used to diagnose glaucoma. perennial allergic conjunctivitis (PAC) One of two types of allergies affecting the eyes. Generally caused by pet dander, dust or other allergens present throughout the year, PAC causes sufferers to experience eye allergy symptoms (i.e., itching, redness, swelling and tearing) year-round. peripheral vision The ability to see objects or motion out of the direct line of vision. Also called "side" vision. phacoemulsification (phaco) The medical term for "small incision cataract surgery." Phaco represents the majority of cataract surgeries performed today. After making a small incision on the side of the cornea, the surgeon inserts a tiny probe into the eye. The probe emits ultrasound waves that soften and break up the clouded lens, which is then removed by suction. An artificial lens (intraocular lens or IOL) is then permanently placed in the eye. phoropter An instrument allowing the eye care professional to place lenses of differing strengths in the patient's view to determine which lens choices make the patient's vision clearer. Results of refractive testing with a phoropter are helpful in diagnosing vision disorders such as hyperopia, myopia, presbyopia and astigmatism and prescribing appropriate corrective lenses (eyeglasses or contact lenses). photodynamic therapy A treatment using a non-thermal (cold) laser and a light-activated drug to destroy abnormal and leaking blood vessels in the eye. Photodynamic therapy is a treatment for wet age-related macular degeneration (AMD). photophobia Abnormal sensitivity to, and discomfort from, light. May be associated with excessive tearing. Often due to inflammation of the iris (iritis) or cornea (keratitis). photorefractive keratectomy (PRK) A type of refractive surgery to correct vision disorders such as myopia, hyperopia and astigmatism. PRK uses an excimer, or non-heat producing laser to remove very small amounts of the corneal layer, reshaping the cornea's curvature. The change in corneal curvature refocuses light (images) on the retina, resulting in improved vision. pink eye The common term for conjunctivitis, a contagious eye infection characterized by inflammation of the lining of the eyelid. Pink eye generally causes redness of the eyelid or white of the eye, increased tear flow, yellow eye discharge and itchy, burning eyes. This condition is generally treated with prescription antibiotic eye drops. power of accommodation The eye's ability to increase optical power in order to maintain a clear image (focus) as objects are moved closer. Occurs through a process of ciliary muscle contraction and zonular relaxation that manipulates the shape of the eye's elastic-like lens. presbyopia A condition in which the eye loses its natural ability to focus properly. Presbyopia is a natural result of aging and causes blurry, close-up vision. Reading glasses or corrective contact lenses are necessary to maintain quality close-range vision once presbyopia has been diagnosed. PRK An acronym for Photorefractive Keratectomy, a refractive surgery procedure that uses an excimer laser to remove tissue directly from the surface of the cornea. proliferative retinopathy The most serious form of diabetic retinopathy characterized by the growth of abnormal, fragile blood vessels on the retina. Vision can be severely impacted, or even lost, if these blood vessels leak blood into the eye or burst. Symptoms may include blurred, distorted vision, the presence of "floaters" in the visual field, partial loss of vision and eye pain. prostaglandins A class of drug that is commonly administered in an eye drop, to lower or control eye pressure, by increasing the flow of fluid between tissues in the eye. puncta The medical term for tear ducts. punctal plugs Small silicon plugs inserted in eye tear ducts to prevent the draining away of natural tears. A method of conserving tears to relieve symptoms of dry eye, punctal plugs help keep the eye's surface moist and lubricated. pupil The part of the eye allowing light to enter. The pupil is the black area of the eye situated in the center of the iris. refraction A measurement to determine refractive error. Refraction measures the eye's focusing abilities and is used to prescribe vision correction, in the form of eyeglasses, contact lenses or refractive surgery. refraction test A test that utilizes a phoropter and a chart at a 20-foot distance to measure the eye's ability to see objects at certain distances. Lenses of different strengths placed in the patient's view then lead to a lens prescription for clear vision. Results of the refraction test can help diagnose vision disorders such as hyperopia, myopia, presbyopia and astigmatism. refractive errors Vision problems caused by an imperfect optical system, most commonly myopia, hyperopia and astigmatism. refractive surgeon An ophthalmologist who specializes in performing refractive procedures such as LASIK. refractive surgery Any surgical procedure performed to change the eye's refractive error. retina The part of the eye that receives images (light) and sends them to the brain for interpretation. The retina is the eye's innermost layout and contains many nerve cells and fibers that are connected to the optic nerve. retinal detachment A serious condition occurring when part of the retina lifts or pulls away from its natural position. Retinal detachment, if left untreated, can result in significant vision impairment or loss within a number of days and can lead to blindness. Symptoms include seeing flashes of light in peripheral (side) vision, a sudden increase in the presence of "floaters," and loss of peripheral vision. ribonucleic acid Also known as ribose nucleic acid or RNA, ribonucleic acid includes any of various nucleic acids that contain ribose and uracil as structural components and are associated with the control of cellular chemical activities. rods Light-sensitive cells in the retina that perform best in darkness or dimly lit conditions. saccadic Involuntary eye movements. These rapid eye movements occur all the time, including during laser refractive surgery and may affect accurate placement of the laser beam. saccadic movements Involuntary eye movements. These rapid eye movements occur all the time, including during laser refractive surgery and may affect accurate placement of the laser beam. sclera The eye's white part. Along with the cornea, the sclera provides external protection for the eye. scleritis Inflammation of the sclera. seasonal allergic conjunctivitis (SAC) One of two types of allergies impacting the eyes. SAC, the most common type of eye allergy, causes sufferers to experience eye allergy symptoms (i.e., itching, redness, swelling and tearing) during certain seasons of the year (spring, summer and early fall) when pollen counts are usually higher. siRNAs Small interfering RNAs make up a class of 20-25 nucleotide-long RNA molecules that play a variety of roles in biology. Most notably, they are involved in the RNA interference pathway (RNAi) where the siRNA interferes with the expression of a specific gene. Their discovery has led to a surge in interest in harnessing RNAi for biomedical research and drug development. spherical aberration A visual disorder reflecting a change in curvature between the center and edge of the pupil. This creates multiple focal points and can cause halos in your vision. sty A painful lump on the eyelid caused by an infection in the oil glands at the base of an eyelash. Not considered very contagious, sties resemble a boil or pimple and normally disappear without medical treatment within a few days. Sties cause a swollen eyelid, light sensitivity, tearing and itching. tonometer A small, smooth instrument placed on the surface of the eye to measure intraocular (eye) pressure. Tonometer readings are used to help diagnose glaucoma. tonometry An exam for measuring intraocular (eye) pressure. Conducted by placing a small, smooth instrument called a tonometer onto the eye's surface, tonometry helps diagnose glaucoma. trabecular meshwork The spongy "drain" situated where the cornea meets the iris. The trabecular meshwork allows for the normal drainage of eye fluid in and out of the eye. When fluid drains too slowly through this meshwork, increased eye pressure – a potential precursor to glaucoma – can result. trachoma A severe, chronic and contagious conjunctival eyelid and corneal infection caused by a virus that leads to corneal blood vessel formation, corneal clouding, conjunctival and eyelid scarring, and dry eyes. uveitis Inflammation of any of the structures of the uvea, including the iris, ciliary body or choroids. uveitis/iritis Inflammation of the iris and other internal structures of the eye. visual acuity Also called central vision. Visual acuity is the eye's ability to distinguish the shape of objects and visual details. This does not include depth perception, peripheral (side) vision or color blindness. vitreous gel or vitreous body The transparent and colorless gelatinous material between the lens and the retina. wavefront device A sophisticated measurement device, which passes a narrow ray of eye-safe light through the optical system and measures the optical distortions as the light exits the eye. With the LADARVision® system, the resulting wavefront maps are used to provide fully customized vision correction, to address both lower- and higher-order aberrations, through the CustomCornea® procedure. wavefront mapping A sophisticated way to represent visual disorders, these maps are created by passing a narrow ray of eye-safe light through the optical system and measuring the optical distortions as the light exits the eye. With the LADARVision® system, the resulting wavefront maps are used to provide fully customized vision correction, to address both lower- and higher-order aberrations, through the CustomCornea® procedure. wet AMD A serious, progressive form of age-related macular degeneration (AMD) causing significant loss of central vision in older adults. Resulting from a growth of abnormal blood vessels under the macula, wet AMD is the most advanced form of AMD.