abscess: A localized collection of pus surrounded by inflamed tissue.

accommodation: The change in the curvature of the crystalline lens that helps to focus images of objects close to the eye.

acquired immunodeficiency syndrome (AIDS): A viral infection characterized by a compromised immune system.

acute: Refers to a condition that flares up suddenly and persists for only a short time.

adnexa: The tissues and structures surrounding the eye; includes the orbit, extraocular muscles, eyelids, and lacrimal apparatus.

age-related macular degeneration: A disease in which sensory cells of the macula degenerate, resulting in a loss of central vision; affects older people.

allergic reaction: A condition in which the body produces antibodies to foreign materials such as food, plant pollens, or medications.

amblyopia: Suppression of vision from one eye.

Amsler grid test: A test for determining the presence and location of defects in the central portion of the visual field.

anesthetic: A drug that causes a temporary deadening of a nerve, resulting in loss of feeling in the surrounding tissue.

anterior: Front.

anterior chamber: The small compartment between the cornea and the iris that if filled with a clear, transparent fluid called aqueous humor.

anterior chamber angle: The junction of the cornea and the iris, from which aqueous humor leaves the eye.  Also called filtration angle.

anterior segment: The front of the eye; includes the structures between the front surface of the cornea and the vitreous.

antibiotic: A drug that combats a bacterial infection.

antibody: The type of chemical that the body manufactures to neutralize an infecting microorganism.

antiviral: A drug that combats a viral infection.

apex: The top, as of a prism.

aphakia: Absence of the lens, usually because of cataract extraction.

aphakic correction: The use of a contact lens, eyeglasses, or an intraocular lens for more normal vision in aphakic patients.

applanation: A form of tonometry in which the force required to flatten a small area of the central cornea is measured.

aqueous humor: The clear, transparent fluid that fills the anterior chamber.

arcus senilis: A common degenerative change in which the outer edge of the cornea gradually becomes opaque, generally in both eyes; affects people over the age of 50.

A-scan ultrasonography: A diagnostic procedure in which sound waves traveling in a straight line are used to reveal the position of, and distances between, structures within the eye and orbit.  Also called A-mode ultrasonography.

aseptic technique: A range of procedures used in medical environments to prevent the spread of infectious microbes.

astigmatism: The refractive error of an eye whose corneal surface curvature is greater in one meridian than another; both distant and near objects appear blurred and distorted.

autoclave: A metal chamber equipped to use steam or gas under high pressure and temperature to destroy microorganisms.

axis: The meridian perpendicular to the meridian with curvature in a cylindrical lens.

bacteria: (singular: bacterium) Primitive, single-celled organisms, widely dispersed in nature; some bacteria are capable of causing disease in humans.

basal cell carcinoma: The most common malignant lid tumor; has a characteristic appearance of a pit surrounded by raised “pearly” edges.

base: The bottom, as of a prism.

base curve: The curve of the lens surface, usually the outer or front side of the lens, from which the other curves necessary for sight correction are calculated.

benign: Refers to any tumor that is not dangerous to the well being of the individual.

bifocal lens: One that has two powers: usually one for correcting distance vision and one for correcting near vision.

binocular vision: The blending of the separate images seen by each eye into one image; occurs when both eyes are directed toward a single target and perfectly aligned.

blepharitis: A common inflammation of the eyelid margin.

blind spot: A small sightless area that is caused by the lack of rods and cones at the head of the optic disc.

blowout fracture: An injury due to blunt trauma, in which orbital bones are broken.

B-scan ultrasonography: A diagnostic procedure that provides two-dimensional reconstruction of ocular and orbital tissues, using radiating sound waves.  Also called B-mode ultrasonography.

  bulbar conjunctiva: The globe portion of the conjunctiva.

  daily-wear lenses: Rigid and soft contact lenses intended to be worn for fewer than 24 consecutive hours while awake.

    decongestant: A drug that constricts the superficial blood vessels in the conjunctiva to reduce eye redness; a cosmetic effect only.

  degenerative: Refers to any process in which the structure or function of body tissues gradually deteriorates.

  dendritic: Branch-shaped, such as the corneal ulcers seen after infection with the herpes simplex virus.

  diabetes mellitus: A condition in which the body is unable to produce enough insulin, the hormone required for the metabolism of sugar.

  diabetic retinopathy: A progression of pathologic changes in the retina; produced by long-standing diabetes mellitus.

  diagnosis: Determination of a medical condition.

  dilator muscle: The iris muscle that dilates the pupil in reduced light conditions; fibers from this muscle stretch from the pupil to the boundaries of the iris.

  diopter: The unit of measure of the power of a lens.

  diplopia: Double vision.

  direct ophthalmoscope: A hand-held instrument with a light-and-mirror system that affords an upright, monocular view of a narrow field of the fundus, magnified 15-fold.

  disease: A specific process in which abnormal changes result in malfunction of a particular part or system of the body.

  disinfection: The process of inactivating or eliminating pathogenic microorganisms.

  disposable lenses: Soft contact lenses designed for either daily or extended wear and then disposal after 1 week to 1 month.

  distometer: An instrument for measuring vertex distance.

drusen: Anatomic defect of the retinal pigment epithelium.

  edema: Swelling caused by a large amount of fluid in a part of the body.

  emergency: A medical situation that requires immediate attention.

  emmetropia: The refractive state of an eye that is able to focus correctly.

  endophthalmitis: A serious ocular bacterial infection with inflammation of the vitreous and adjacent tissues.

  entropion: A condition in which the upper or lower lid margin is turned inward.

  esophoria: The inward deviation of the eye that is present only when one eye is covered.

  esotropia: The inward deviation of the eye in which the eyes are misaligned even when uncovered.

  exophoria: The outward deviation of the eye that is present only when one eye is covered.

  exophthalmometer: An instrument that measures the prominence of the eyeball in relation to the bony orbital rim surrounding it.

  exotropia: The outward deviation of the eye in which the eyes are misaligned even when uncovered.

  extended-wear lenses: Soft contact lenses that are approved for overnight wear for up to 7 days.

  extraocular muscles: The six muscles that attach to the outside of the globe and control its movements.

  eyeball: See globe.

  eyelid: The moving fold of skin that covers the outer portion of the globe.

  flashlight test: A simple test for estimating the depth of the anterior chamber and the chamber angle.

  floaters: Small particles of dead cells or other debris that become suspended in vitreous, or particles of the vitreous itself that degenerate in the normal aging process; they cast shadows on the retina and appear as spots or cobwebs.

  flora: See normal flora.

  fluorescein: A dye solution that is used in applanation tonometry; also used intravenously in fluorescein angiography to identify abnormal blood vessels.

  fluorescein angiography: Diagnostic photography of retinal vessels that requires injection of fluorescein dye.

  focal length: The distance between the focal point and the lens.

  focal point: The point somewhere along the principal axis at which the paraxial rays from a distant source are refracted by a lens and converge in the case of a convex lens and diverge in the case of a concave lens.

  foreign-body sensation: A feeling of eye irritation or grittiness.

  fornix: The loose pocket of conjunctival tissue where the eyelid and globe portions of the conjunctiva meet beneath the upper and lower lids.  Also called cul-de-sac.

  fovea: The center of the macula.

  fundus: A collective term for the retina, optic disc, and macula.

  funduscopic examination: Examination of the vitreous and fundus by ophthalmoscope.  Also called posterior segment examination.

  fungus: (plural: fungi)  A multicelled microorganism that differs from a bacterium in that it has a more complex structure and reproduces sexually and asexually; includes yeasts and molds.  Some can live inside the body and cause infection.

  fusion: The blending by the brain of the separate images received by the two eyes so that a single view is perceived even when the eyes move.

genetic: Refers to a trait that is inherited from either or both parents.

  giant papillary conjunctivitis (GPC): Inflammation of the tarsal conjunctiva, characterized by large raised bumps.

  glare testing: A procedure for assessing a patient’s vision in the presence of a bright light source to determine whether sensitivity to glare is contributing to visual symptoms.

  glaucoma: An eye disease in which the intraocular pressure is high enough to cause damage to the optic nerve, resulting in visual loss; caused by impaired drainage of the aqueous fluid out of the eye.

  Goldmann tonometer: An applanation tonometer that measures corneal flattening to determine intraocular pressure.

  gonioscopy: A method of viewing the chamber angle through a special contact lens placed on the anesthetized eye.

  GPC: See giant papillary conjunctivitis.

  granuloma: A firm collection of a specific kind of inflammatory cell.

  Grave’s disease: A condition of unknown origin that involves the thyroid gland and causes the soft tissues surrounding the globe to swell.

  herpes simplex virus: In ophthalmology, a type of virus that infects the cornea, producing branch-like ulcers (dendritic keratitis).

  HIV: See human immunodeficiency virus.

  human immunodeficiency virus (HIV): A virus that causes a deficiency of the immune system, making the patient susceptible to a variety of opportunistic infections of various tissues, including the retina.

  hyperopia: Farsightedness; the eye is too short for its optical system.

  hyphema: The pooling of blood in the anterior chamber as a result of trauma or certain diseases.

  hypopyon: The accumulation of pus in the anterior chamber.

  indentation: A form of tonometry in which the amount of corneal indentation produced by a fixed weight is measured.

  indirect ophthalmoscope: An instrument that affords an inverted but wider view of the fundus than does the direct ophthalmoscope.

  infection: The invasion and multiplication of harmful microorganisms in the body tissues: a local bacterial or fungal infection begins in the tissues immediately surrounding the microorganism’s point of entry; if unchecked, the infection may spread to surrounding tissues, thereby becoming diffuse.

  inflammation: A local protective tissue response to infection, in which specialized cells move to the affected area to destroy the injurious agent, while other cells release fluids to dilute any toxic substances produced by the infectious agent and wall off both the offender and the damaged tissue.

  informed consent: The process by which, after discussion with the physician about the risks and benefits of a proposed procedure, the patient agrees to undergo a treatment.

  injection: The delivery system by which a drug is injected into the body with a hypodermic needle.

  injury: Damage to or destruction of cells that compose a tissue, organ, or system.

  insulin: A hormone the body uses to metabolize sugar.

  internal hordeolum: A lump on the inner or outer eyelid; caused by inflammation and infection of a meibomian gland.

  interpupillary distance (IPD or PD): The distance from the center of the pupil of one eye to the center of the pupil of the other eye.

  intraocular pressure: Fluid pressure within the eye.

  invisible bifocal: A bifocal lens with a softened or blended transitional zone between the segment and the distance portion.  Also called seamless bifocal or blended bifocal.

  iridotomy: A type pf laser surgery used to open the anterior chamber angle of patients with glaucoma.

  iris: The colored circle of tissue that controls the amount of light entering the eye by enlarging or reducing the size of its aperture, the pupil.

  iritis: Inflammation of the iris.

  ischemia: A condition in which the supply of blood to a part of the body is severely reduced.

Keratoconus: A rare degenerative corneal disease in which the center of the cornea thins and assumes the shape of a cone, seriously affecting vision.

  keratometer: An instrument used to measure corneal curvature.  Also call ophthalmometer.

  keratometry: The measurement of corneal curvature.

  lacrimal gland: The gland that produces the watery substance making up the middle layer of the tear film; located in the lateral part of the upper lid.

  lacrimal probe: An instrument for exploring and clearing an obstruction of the tear duct.

  lacrimal sac: The sac that holds tears after they pass through the canaliculi, which empty through the nasolacrimal duct into the nasal cavity.

  legal blindness: A best-corrected visual acuity of 20/200 or less or a visual field reduced to 20° or less in the better-seeing eye.

  lens: Part of the optical focusing system of the eye, immediately behind the iris.  Also called crystalline lens.

  lensmeter: An instrument for measuring the prescription of eyeglass lenses or the power of rigid contact lenses.

  lensometry: The measurement of certain qualities of lenses by the use of a lensmeter.

  lesion: An abnormal tissue or a break in a normal tissue.

low vision: A reduction of central vision, side vision, or both, that may require more than glasses or contact lenses to see well enough to get around and do day-to-day tasks.

  malignant: Refers to any tumor that is cancerous and has the potential of spreading to other parts of the body.

  manifest refraction: Refractometry performed without the use of cycloplegic drugs.

  medial canthus: See canthus.

  media opacities: The general term used to describe a variety of conditions that cloud, obscure, or otherwise affect the ocular media and , ultimately, may disrupt vision.

  meibomian gland: A specialized gland that secretes the oily part of the tear film that lubricates the outer surface of the globe; located on the inner margin of the eyelid (the edge closest to the globe).

  metabolism: The physical and chemical processes by which the body converts food into energy and new body tissues.

  metastasis: The process by which cancerous cells move to other parts of the body and produce new tumors.

  microorganism: An extremely small life form invisible to the unaided eye.  Also called microbe.

  miotic: A drug that causes the iris sphincter muscle to contract, producing miosis (pupillary constriction), which reduces the amount of light entering the eye.

  mydriatic: A drug that dilates the pupil.

  myopia: Nearsightedness; the eye is too long for its optical system.

  near visual acuity: The ability to see clearly at a normal reading distance.

  neoplasm: A new growth of different or abnormal tissue, such as a tumor or wart.

  neovascularization: The abnormal growth of new blood vessels.

  neutralization: See lensometry.

  nevi: (singular: nevus)  Literally, freckles; common tumors involving the bulbar conjunctiva and appearing as yellowish pink or brown areas on the conjunctiva or skin.

night blindness: Inefficient dark adaptation that results in reduced vision in dim light.

  normal flora: Microorganisms that colonize part of a host’s body without producing disease.

  nystagmus: A condition in which the eyes continually drift in a side-to-side or up-and-down motion and then snap back to the normal position.

  ocularist: A professional who measures and fits patients with an artificial eye (prosthesis) to replace an absent eye or cover an unsightly one.

  OD (oculus dexter): Latin for right eye.

  ophthalmic medical assistant: A professional who assists the ophthalmologist in a variety of diagnostic and administrative tasks, including performing certain tests, administering certain topical medications or diagnostic drugs, and helping with office surgical procedures.

  ophthalmic photographer: A professional who photographs eye structures for diagnosis and documentation.

  ophthalmic registered nurse: A registered nurse with special training in problems related to the eye; frequently functions as a surgical assistant to an ophthalmologist, a director of an ophthalmic surgery service, or a director of clinical services.

  ophthalmologist: A medical doctor (MD or DO) who specializes in the prevention, diagnosis, and medical as well as surgical treatment of vision problems and diseases of the eye.

  ophthalmology: The medical and surgical specialty concerned with the eye and its surrounding structures, their proper function, eye disorders, and all aspects of vision.

  ophthalmoscope: An instrument for examining directly or indirectly the vitreous and fundus.

optic cup: White depression in the center of optic disc.

  optical center: The point of optimal vision; the single point of a lens through which light may pass without being bent or changed.

  optic disc: The location where the central retinal artery enters and the central retinal vein, as well as the nerve fibers, exits.  Also called optic nerve head.

  optician: An independent professional licensed to dispense eyeglasses and contact lenses from the prescription of an ophthalmologist or optometrist.

  optic nerve: The nerve that carries electric impulses to the brain’s visual cortex, where they are integrated to produce the sensation of sight.

  optic nerve head: See optic disc.

  optic neuritis: Inflammation of the optic nerve; can produce a sudden, but reversible, loss of sight.

  optics: The branch of physical science that deals with the properties of light and vision.

  optometrist: An independent practitioner trained in the prescription of eyeglasses and contact lenses as well as in the detection of eye disease.

  orbit: The bony cavity in the skull that houses the globe, extraocular muscles, blood vessels, and nerves.

  orbital cellulitis: A diffuse infection of tissues in the orbit, causing grossly swollen eyelids and red eye, sometimes without proptosis.

  orthoptist: A professional who works under the direction of an ophthalmologist to help with the diagnosis, management, and nonsurgical treatment of eye muscle imbalance and related visual impairments.

  OS (oculus sinister): Latin for left eye.

  palsy: Paralysis.

papilledema: A swelling of the optic disc with engorged blood vessels; caused by increased fluid pressure within the skull.

  papoose board: A padded board with Velcro straps; used for immobilizing an infant during an ophthalmologic examination.

  parallel: Refers to rays that travel side by side in the same direction, neither diverging nor converging.

  parasites: Organisms that rely on another animal or a plant for nutrients and conditions necessary for survival.

  pathologic: Abnormal.

  perimetry: The measurement of the expanse and sensitivity of peripheral vision and the visual field to pinpoint possible defects.

  peripheral vision: The visual perception of objects and space that surround the direct line of sight.

  pharmacology: The study of the medicinal use and actions of drugs (medications).

  photocoagulation: Surgical welding with laser light beams.

  photorefractive keratectomy: A type of refractive surgery that employs laser light instead of surgical knives to reshape the corneal curvature; also referred to as PRK.

  physiologic blind spot: The sightless “hole” in the normal visual field corresponding to the optic disc.

  pigment epithelium: The outer layer of the retina; lies against the choroid.

  pinguecula: A small, benign, yellow-white mass of degenerated tissue beneath the bulbar conjunctiva, just nasal or temporal to the limbus.

  “pink eye”: See conjunctivitis.

  polarized: Refers to lenses made of plastic, glass, or photochromic glass that is specially manufactured to reduce glare, brightness, and ultraviolet light transmission.

  posterior: Back.

  posterior chamber: The space between the back of the iris and the front of the vitreous; the crystalline lens is suspended in this chamber, which is filled with aqueous fluid.

  posterior segment: The rear portion of the eye; includes the vitreous and the retina.

  potential acuity meter: A device for determining visual acuity in the presence of media opacities.

  presbyopia: The progressive loss of the accommodative ability of the lens; due to natural processes of aging.

  primary open-angle glaucoma: A form of glaucoma in which the pressure inside the eye is elevated because of increased resistance to aqueous drainage in the outflow channels; accounts for 60% to 90% of all adult glaucomas.

  prism: A triangular piece of glass or plastic with flat sides, an apex, and a base.

  prism diopter: The unit of measure of the refractive power of a prism.

  prognosis: Prediction of the outcome of a medical condition.

  proptosis: A condition characterized by a protruding eyeball; caused by an increase in volume of the orbital contents.  Also called exophthalmos.

  pseudoisochromatic color plates: A book of plates that display patterns of colored and gray dots; used for evaluating color vision.

  pseudophakia: The use of an intraocular lens to correct the vision of an aphakic patient.

  pterygium: A wedge-shaped growth on the bulbar conjunctiva.

  ptosis: Drooping of and inability to raise the upper eyelid; caused by the levator muscle’s inability to function.

  punctum: (plural: puncta)  The tiny opening on the upper eyelid margin (upper punctum) and lower eyelid margin (lower punctum) near the nose, from which tears pass.

  pupil: The opening in the center of the iris that enlarges (admitting more light) and reduces (admitting less light).

  refinement: The second step in refractometry, requiring patient participation and responses, which confirms the information produced by retinoscopy.  Also called subjective refractometry.

  refracted: Refers to a light ray that bends when it passes at an angle from one transparent medium to another.

refraction: (1) In physics, the bending of a light ray as it passes through substances of different densities.  (2) In eye care, the process of measuring a patient’s refractive error and the clinical judgment to determine the optical correction needed.

  refractive error: A nonpathologic deficiency in the eye’s optical system.

  refractive state: The relative ability of the refractive components of the eye to bring objects into focus on the retina.

  refractive surgery: A type of corneal surgery that modifies the shape of the cornea to correct some types of myopia, hyperopia, and astigmatism.

  refractometry: The measurement of refractive error with a variety of instruments and techniques.

  refractor: An instrument for determining a corrective lens prescription; stores a range of trail lenses that can be dialed into position.  Also called phoropter.

  regular astigmatism: The most common form of astigmatism, in which the cornea resembles a football standing on one end or on its side.

  retina: The inner lining of the eyeball; consists of a layer of light-sensitive cells that convert images from the optical system into electric impulses sent along the optic nerve for transmission to the brain.

  retinal detachment: The separation of the sensory layer from the pigment layer of the retina.

retinal pigment epithelium: Pigment cell layer just outside the retina that nourishes retinal visual cells.

retinitis: Inflammation of the retina.

  retinitis pigmentosa: A hereditary, progressive retinal degeneration that may lead to blindness.

retinoscope: An instrument for measuring refractive error; consists of a light source and a viewing component.

  retinoscopy: The use of retinoscope to determine a refractive error; the first step in refractometry.  Also called objective refractometry.

  retrobulbar: Behind the eye.

  RGP: See rigid gas-permeable lenses.

  rigid gas-permeable (RGP) lenses: Contact lenses that permit oxygen and carbon dioxide diffusion through both the lens material and a tear pump.

  RK: See radial keratotomy.

  rod: The retinal photoreceptor largely responsible for vision in dim light (“night vision”) and for peripheral vision.

  sclera: The white tissue surrounding the cornea; protects the intraocular contents and forms the wall of the eye.

  scleral buckle: A surgical procedure for correcting retinal detachment that involves placing a block of silicone or other material on the eye to indent the wall.

  scleritis: Inflammation of the sclera.

  secondary glaucoma: Glaucoma that occurs secondary to another, primary disease.

  segment height: The distance between the lowest part of an eyeglass rim and the top of the multifocal lens segment.

sign: An abnormal change observed objectively by the physician on examination of the patient.

  single lines: The closely spaced mires in a lensmeter.

  sinus: A bony cavern of the skull that contains air and connects with the nasal passages.

  slit lamp: An instrument used for close examination of the lids and lashes, cornea, lens, membranes, and clear fluids within the eye; consists of a microscope of low magnifying power and a light source that projects a rectangular beam that changes in size and focus.  Also called biomicroscope.

  Snellen chart: A printed visual acuity chart consisting of Snellen optotypes – specially formed letters of the alphabet arranged in rows of decreasing letter size.

  soft lenses: Flexible contact lenses that permit oxygen and carbon dioxide diffusion through the lens material itself, with a minimal tear pump.

  spectacle blur: Temporary blurred vision upon switching from contact lenses to eyeglasses.

  specular microscopy/photography: A method of microscopically photographing the cornea’s endothelial cells at great magnification and producing photographs on which the cells can be counted.

  spherical cornea: A cornea (of the normal eye and most myopic and hyperopic eyes) whose curvature is uniform.

  stereopsis: The ability to perceive depth visually in three dimensions.

  sterilization: The destruction of all microorganisms by various methods.

  strabismus: A misalignment of the eyes that may cause vision to be disturbed; occurs when the extraocular muscles do not work in a coordinated manner.

  stye: A reddened, sore lump near the outer edge of the eyelid; caused by an inflamed lash follicle.  Also called external hordeolum.

  subconjunctival hemorrhage: A rupture of a conjunctival blood vessel that allows blood to flow under the tissue and produces a bright-red flat area on the conjunctiva.

  suture: To stitch a wound closed; the pattern of the stitch; or the thread-like material used to make the stitch.

  symptom: A change in vision, pain, or other subjective effect that indicates a disease process.

  syndrome: A set of signs or symptoms that is characteristic of a specific condition or disease.