This vision glossary has been reprinted with the permission from Lynn Fishmann Hellerstein, OD, FCOVD, and the Optometric Extension Program Foundation.

  • ABILITY – Developed capacity
  • ABNORMAL RETINAL CORRESPONDENCE (ARC) – There is a disruption of the above and the patient reports that he/she is using the fovea of one eye together with a retinal area in the indirect field of his/her other eye
  • ACCOMMODATION – The act of changing the focus inside the eye so as to obtain clear vision in each eye when the gaze is shifted from one distance to another; i.e., from near to distance or distance to near and all distances in between
  • ACCOMMODATIVE ROCK – A test studying flexibility of the patient in changing focus; also the therapy for this ability
  • ACUITY – Clearness of vision (Standard is 20/20, which means the individual sees at 20 feet what most people can see at that same distance.)
  • ADAPTATION – The point where the mediator establisher a level between stimulus and response
  • ADAPTIVE PROCESS – The maneuvers (conscious or unconscious, automatic or voluntary) by which the individual attempts to make the organismic decisions as comfortable and gratifying as possible within the demands of that individual’s environment
  • ADJUSTER – Another name of a nerve center
  • ADVENTITIOUS – Acquired (a refractive error or tropia that is not congenital, or due to trauma or infection but occurs because of environmental impact)
  • ALIGNMENT – The placing of the retinal quadrants of the eye so that the light stimulus is equally distributed on all four quadrants
  • AMBLYOPIA – A muscular disorder whereby certain muscles of the eye become useless through lack of coordination or non-use (also called “lazy eye”)
  • AMPLITUDE, FUNCTIONAL (or ANALYTICAL) -The range over which clear, binocular vision can be maintained upon reading material of 20/40 angular size placed at a fixed distance (usually 13 inches)
  • AMPLITUDE OF ACCOMMODATION – The range over which the patient can change focus
  • ANALYSIS – A scientific procedure for dividing a complex experience into simpler constituents
  • ANALYTICAL EXAMINATION – The 21-point optometric examination (Each point is a measurement of performance of a visual behavior pattern. These measurements, made through the application of prism and sphere, show the absorption of the potential of inhibition, measure the existing learned associations between patterns, and probe for the degree or organization existing in the visual pattern.)
  • ANISEIKONIA – The image of an object as seen by one eye is different in size and shape from the other one
  • ANISOMETROPIA – A condition of unequal refractive state for the two eyes, one eye requiring a different lens correction from the other
  • ANOMALY – Any striking deviation from typical or normal
  • ANTIMETROPIA – One eye is nearsighted and the other is farsighted
  • ANTERIOR CHAMBER – The pocket behind the pupil and cornea extending to the iris and separated from the posterior chamber by the iris
  • AQUEOUS HUMOR – The watery fluid that fills the anterior and posterior chamber (It is formed by the ciliary process and passes through the posterior chamber and the pupil to the anteriio chamber where it is reabsorbed into the venous system by way of the Canal of Schlemm.)
  • ASEPSIS – Free from, absence of, infection or infectious material
  • ASSISTANT – One who helps, aids of gives support to another (What really makes us true optometric assistants is a great understanding of the optometric profession and a willingness to give of ourselves in order that others may benefit.)
  • ASTIGMATISM – A defect in the eye whereby the light rays from an object are not brought to a single image point (condition where one part of the field is more out of focus than other parts. Clearness of vision can generally be restored by lenses.)
  • AXIS – An imaginary straight line passing through a body or a system with respect to which this body or system is symmetrical
  • BACTERIA – One-cell organism, some of which are disease producing
  • BASE CURVE – When applied to a toric surface, the base curve is the weakest curve of the surface. When applied to lenses in general, the base curve is the curve common to a group of lenses.
  • BEHAVIOR – The reaction of the individual to his environment (all types of muscular and glandular responses of the organism to stimulation)
  • BELL RETINOSCOPY – A variation of dynamic retinoscopy in which the test object is moved toward the patient while the retinocsope is kept at a fixed distance
  • BIFOCAL – Any lens containing two different powers for focusing at different distances
  • BINOCULAR – Refers to the unification of the right and left fields of view
  • BLIND SPOT – A certain portion of the retina where light rays focused will not be transmitted through the optic nerve; every individual has such a blind spot, but it may enlarge through disease or trauma (also called the optic disk)
  • BLOCKING – Inhibition
  • BLUR – Lack of clearness of the object of regard
  • BLUR POINT – Under a given set of test conditions, the point at which the fixation target appears blurred on the introduction of gradually increasing prism and/or lens power
  • BOOK RETINOSCOPY – Retinoscopy performed while the subject is reading
  • BREAK POINT – The point at which diplopia occurs on gradually varying the prism or lens power during binocular fixation
  • CANTHUS – The angle formed by the juncture of the eyelids
  • CAPACITY – Potential or latent ability
  • CASE ANALYSIS – A study of visual performance
  • CATARACT – The condition of the eye whereby the crystalline lens loses transparency and obstructs the passage of light
  • CENTERING – Selection of some area of space for attention and meaning (the computing process of “Where is it?”)
  • CENTIMETER (cm.) – In the metric system, the hundredth part of a meter (.3937 inches)
  • CENTRAL VISUAL FIELD – The area directly ahead in which the individual can see sharply and clearly, as opposed to peripheral field, or larger field, over which on can see indistinctly
  • CHAINING – Process of arranging the significant examination findings above or below a horizontal line (used in analyzing cases)
  • CHECKING – Marking the analytical findings which vary from the expected results of the tests
  • CHEIROSCOPIC TRACKING – A vision therapy technique that involves hand-eye coordination in which a pattern is presented to one eye and the projected image is traced before the other eye
  • CHOROID – The layer of cells between the retina and the sclera
  • COMPREHENSION – The understanding of a written text through reading
  • CONCAVE LENSES OR MINUS – A minifying lens that is designed to correct nearsightedness
  • CONJUNCTIVA – The mucous membrane covering the anterior surface of thee eye (bulbar) and lining of the lids (palpebral)
  • CONJUNCTIVITIS – The inflammation of the conjunctiva; also called “Pink eye”
  • CONVERGENCE – Aiming of the eyes to see singly at a given distance
  • CONVERGENCE INSUFFICIENCY – An inability to adequately converge (turn the eyes inward) or to sustain convergence for near visual tasks
  • CONVEX LENSES OR PLUS – A magnifying lens that is used to correct farsightedness
  • CORNEA – The transparent bulge of the front surface of the eye which represents the first part of the optical system and covers the iris and pupil
  • CORNEAL ASTIGMATISM – Defect in the curvature of the cornea whereby light rays passing through the cornea produce aberrations and are not focused on the retina
  • CORTICAL – Within the central nervous system
  • CORTICAL LEVEL – Conscious level
  • CRYSTALLINE LENS – A membrane lens which acts like the lens of a camera; the lens flexes to focus parallel light on the retina
  • CYLINDER LENS – A lens that is designed to correct astigmatism. (Made in plus and minus with designated + or – preceding the power. It is always followed by an axis which is the direction in which there is no power of the cylinder.)
  • DESCEMET’S MEMBRANE – The middle cell layer of the cornea
  • DECENTRATION – The process by which the optical center of the lens is matched with the center of the patient’s pupil
  • DEFECT – An impairment of performance forced on the organism from whatever cause
  • DEVELOPMENT – The modification of growth by the activities and experiences through which the organism goes at various times
  • DEVELOPMENTAL OPTOMETRY – A phase of functional optometry which holds that visual skills are learned performances which develop most effectively if under systematic professional guidance
  • DIAGNOSIS – The procedure by which the nature of disease or disorder is determined by study of its origin, its evolution, and the signs and symptoms manifested by it
  • DIOPTER – A unit of measurement to designate the refractive power of a lens or an optical system, the number of diopters of power being equal to the reciprocal of the focal length in meters; thus a 1 Diopt lens has a focal length of 1 m.
  • DIPLOPIA – The condition in which a single object is perceived as two objects rather than as one; double vision
  • DIRECT FIELD OF VISION – That portion of the field which is seen by the macula
  • DISSOCIATION – Separating the binocular space lattice into two binocular ones
  • DUCTIONS – Measured with bases-out and bases-in prisms to the point where the patient sees two images, then gradually reduced until the two images fuse (break and recovery)
  • DYNAMIC RETINOSCOPY – Retinoscopy performed while the subject fixates a near object
  • DYSLEXIA – A condition in which letters but not words may be read, or in which words may be read but not understood
  • ECCENTRIC FIXATION – The person fixates the image of regard with an area other than the fovea
  • EMMETROPE – An individual who has best visual acuity distance without minus lenses, and blur when plus lenses are applied
  • EMMETROPIA – Theoretically normal eyesight
  • ENDOTHELIUM – The cells which line the base layer of the cornea
  • ENUCLEATION – The removal of the entire eye
  • EPITHELIUM – The cells covering the outermost portion of the cornea
  • ESOTROPIA – A condition where one eye, or both, turns inward
  • EXOTROPIA – A condition where one eye, or both, turns outward
  • FARPOINT – The point upon the visual axis of the eye which is sharply imaged on the retina when the accommodation is relaxed. The far point of a normal eye lies at infinity
  • FARSIGHTED – Also called hyperopia, a condition where light rays focus behind the retina of the unaided eye
  • FIELD STUDIES – Used to determine the area within which objects are more or less distinctly seen by the eye in a fixed position
  • FIXATION – The process, condition or act of directing the eye toward the object of regard, causing, in a normal eye, the image of the object to be centered on the fovea
  • FIXATION, ECCENTRIC – The person fixates the image of the object of regard with an area other than the fovea
  • FOCAL POINT – The point of convergence or divergence of a pencil of light
  • FOCUS – The point at which a pencil of rays or their prolongations can be made to meet after reflection or refraction
  • FOVEA – The study of a tiny spot in the center of the macula through which vision is the sharpest (To see as clearly as possible, each eye must be turned so that the image of the object of regard falls directly upon it.) Color vision occurs here
  • FUSION – Ability to perceive one object seen with the two eyes as a single object
  • HETEROPHORIA – A muscular imbalance exists; however, the person can overcome it and still maintain approximately normal single binocular vision
  • HOROPTOR – The sum total of points in space which can be seen singly by two eyes
  • HYPEROPIA – The condition in which distant objects remain clear as plus lenses are added (same as farsighted)
  • HYPERPHORIA – A tendency of one eye to turn above the other
  • HYPERTROPIA – One eye is actually turned above the other
  • INDIRECT FIELD OF VISION – The area outside the paramacular field
  • INNATE – Patterns of behavior which are present at birth and are, therefore, present prior to experience
  • IRIS – The colored membrane surrounding the pupil which acts like a camera shutter regulating the light entering the eye
  • LACRIMAL GLANDS – The glandular system responsible for tearing
  • LAG OF ACCOMMODATION – An amount that is subtracted from gross nearpoint accommodative tests
  • LOCALIZATION – The placing of a source of stimulation with reference to the organism
  • MACULA – The tiny area in back of the retina in which the nerve endings are more tightly packed than anywhere else in the retina, and through which normally the power to discriminate details is keen
  • MATURATION – The process of growth whereby the state of complete development is attained
  • METER – Basic unit of length in the metric system, equivalent to 39.37 inches
  • MILLIMETER – One-thousandth of a meter (roughly 25 millimeters to one inch)
  • MINUS – Term used to indicate the power of a concave surface or power of a lens whose concave surface is stronger than its convex surface
  • MINUS LENS – (Concave) Changes path of light so that the focus is on the same side of the lens as is the object and closer to the lens than the object
  • MONOCULAR – Pertaining to vision with one eye alone
  • MOTILITY – The directed, integrated, rhythmic behavior of an organism
  • MULTI VISION – Lenses designed with two or more foci
  • MYOPIA – Condition wherein minus lenses are required to restore maximum distance visual acuity (same as nearsighted)
  • NORMAL RETINAL CORRESPONDENCE (NRC) – The foveas and other corresponding areas of the two retinas are linked together so that when the images of an object fall upon them, fusion is achieved
  • OCULAR DEFECTS – The end result of visual problems
  • OCULOMOTOR DYSFUNCTION – Medical name for eye-tracking difficulties
  • OD (oculus dexter) – Abbreviation meaning right eye
  • D. – Doctor of Optometry
  • OS (oculus sinister) – Abbreviation meaning left eye
  • OU (oculi uterque) – Abbreviation meaning both eyes, together
  • OPHTHALMIC – Pertaining to the eye
  • OPHTHALMOLOGIST – A physician specializing in ophthalmology
  • OPHTHALMOLOGY – The medical specialty that deals with diseases of the eye and eye surgery
  • OPTIC NERVE – The part of the nervous system which transmits the impulses of sight from the retina to the brain
  • OPTICAL CENTER – The direct center of an optical lens (Note: It is not the geometric center, but the point on the lens in which the light passes directly through without bending)
  • OPTICIAN – One who assembles spectacles and dispenses them to patients
  • OPTOMETRIST – One who has a professional degree as Doctor of Optometry (O.D.) and cares for vision through the prescription of vision therapy procedures, including lenses whenever appropriate
  • ORGANISM – Any living thing, either animal or plant
  • ORTHOPHORIA – The loss of potential ability to manipulate space beyond the plane of regard (The position of the eyes is not changed when the binocular space lattice is ruptured. It is a condition significant of the absorption of exophoria. It is a signal that a distortion exists in the visual pattern.)
  • ORTHOPTICS – The evaluation and nonsurgical treatment of visual disorders caused by imbalance of the eye muscles
  • PALPEBRAL FISSURE – The point where upper and lower eyelids meet
  • PARAMACULAR FIELD OF VISION – The portion of the field which is immediately adjacent to and surrounds the macula
  • D. – (Interpupillary Distance) The distance between the pupils of the two eyes
  • D. RULE – A ruler having a scale both in millimeters and inches (used to measure the distance between the two eyes)
  • PERCEPTION – Information received through the sense organs
  • PERIPHERAL VISION FIELD – The area of vision lying just outside the line of direct sight
  • PHORIA – Change in overt action in space (It informs as to how much accommodation may be changed with a lens, without causing an overt change in convergence. Phorias are measurements of the relationships existing to protect the integrity of convergence pattern.)
  • PLANO – A lens with no refractive power; with neither plus or minus correction
  • PLUS – The power of a convex surface or power of a lens whose convex surface is stronger than its concave surface
  • PLUS LENS – (Convex) In an optometric prescription it produces an image more distant than the object
  • PRESBYOPE – An individual who, because of age, cannot read standard type (20/20) at near with his basic finding (subjective) and to whom standard acuity can be restored by the use of plus lenses
  • PRESBYOPIA – Due to age the crystalline lens of the eye loses elasticity and loses its power to accommodate for near objects so that they can be seen more clearly. (A bifocal with plus power can correct this problem)
  • PRISM – An optical device which changes the direction but not the distance of the object (Used binocularly, bases-in prism changes condition as though the object were moved farther away; bases-out changes condition as though the object were moved closer.)
  • PRISM DIOPTER – The unit of measurement of prism power (A prism whose power is one prism diopter produces a deviation of one centimeter at a distance of one meter.)
  • PROGNOSIS – A prediction as to the probable outcome of a treatment program
  • PUPIL – The black circular aperture under the cornea through which light enters the eye
  • READING – The vicarious transfer of one person’s visual space world to another person through the use of the visual signs of language
  • RECEPTOR – A sense organ, such as the eye
  • RECOVERY – The return to single vision after doubling is produced by the use of prisms
  • REFLEX- A local movement produced by stimulation of the part in question (a stereotyped contraction of an isolated group of muscles)
  • REFRACTION – The ability of the eye to refract light entering it, so as to form an image on the retina (the measuring of the degree of refraction of an eye)
  • RESIDUAL ASTIGMATISM – The amount of astigmatism present other than that produced by the corneal toricity
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  • RETARDED READER – A person with excellent acuity, high degree of binocular vision, but whose ability to interpret (to get meaning from the printed page) is below his/her age, grade, or intelligence level
  • RETINA – The light sensitive membrane of the eye which receives the image formed by the optical system of the eye and is connected to the brain by the optic nerve
  • RETINOSCOPY – The determination of the conjugate focus of the retina, hence the objective measurement of the refractive state of the eye, with a retinoscope
  • ROTATIONS – The ability of the eye to follow a smoothly moving target in a circular pattern (It is one of the basic visual skills.)
  • SACCADE – An abrupt voluntary shift in fixation from one point to another, as occurs in reading
  • SCLERA – The dense fibrous opaque white outer coat enclosing the eyeball except the part covered by the cornea
  • SCOTOMA – An isolated area of varying size and shape, within the visual field, in which vision is absent or reduced
  • SEEING – The identification of reflected light; and an activity of the human body and mind (Its end result is human behavior in its fullest sense.)
  • SINGLE BINOCULAR VISION – The attainment of single vision through the use of both eyes is the end result of fusion
  • SKILL – A developed or acquired aptitude or ability; a motor performance that has become facile and well integrated; ease and precision in performance of motor acts; the ability to bring about some end result with maximum certainty and minimum outlay of energy
  • SNELLEN CHART – A standard chart of block letters used to measure visual acuity
  • SPACTIC MOVEMENTS – Tension type movements
  • SPATIAL – Of or pertaining to space
  • SPHERE – A lens with equal power in all meridians (whereas a cylinder has maximum power in one meridian and no power in the meridian 90 degrees away.)
  • STANDARD PRACTICE – The “way it is done,” the customary procedure in performing a test
  • STEREOPSIS – Depth perception; tridimensionality—the accurate location of objects in space
  • STIMULI – Forces that act on the sense organs
  • STRABISMUS – A muscle disorder producing an eye that turns inward or outward.
  • STRESS – Any conditions impinging on the organism which require adjustive reactions
  • SUBJECTIVE – The greatest amount of plus lens or the least amount of minus lens through which the patient obtains best acuity at 20 feet (#7 finding in the analytical examination)
  • SUPPRESSION – A type of condition where areas of the total perceptual field have been eliminated by the organism
  • SYMPTONS – The answers given by the modified organism to definite demands, a structural or functional change that indicates the presence of an anomalous condition
  • SYNDROME – A characteristic sequence of symptoms grouped for case analysis
  • TEMPLES – Parts of a frame, extending over ears, which hold the spectacles in place
  • THERAPY – The treatment of disease or any physical or mental disorder by medical or physical means; the arranging of conditions that through repeated experience the individual may teach himself
  • TRIFOCAL – A lens which has three different optical powers
  • TROPIA -A turning of one or both of the eyes (strabismus, or squint)
  • VERSIONS – The ability to fixate quickly and accurately with both eyes on a series of fixed objects—one after another—like figures on a scoreboard, or map, or blue print (This saccadic ability is also trainable.)
  • VISAGRAPH III – An eye-movement recording system that measures the efficiency of silent reading
  • VISION – The special sense by which objects, their form, color, position, etc., in the external environment are perceived, the exciting stimulus being light from the objects striking the retina of the eye; the act, function, process, or power of seeing; sight
  • VISION THERAPY – Vision therapy is a sequence of neurosensory and neuromuscular activities individually prescribed and monitored by the doctor to develop, rehabilitate and enhance visual skills and processing. The vision therapy program is based on the results of a comprehensive eye examination or consultation, and takes into consideration the results of standardized tests, the needs of the patient, and the patient’s signs and symptoms. The use of lenses, prisms, filters, occluders, specialized instruments, and computer programs is an integral part of vision therapy. The length of the therapy program varies depending on the severity of the diagnosed conditions, typically ranging from several months to longer periods of time. Activities paralleling in-office techniques are typically taught to the patient to be practiced at home, thereby reinforcing the developing visual skills.
  • VISUAL ACHIEVEMENT – The ability to interpret the external visual environment by means of the photo (light) receptor
  • VISUAL ACUITY – The ability to discriminate contours; to tell when there is separation from background and whether there are one, two or three objects and not just a blur (It is the ability to perceive the interspace between two objects when it is very small. It is the reciprocal of the just resolvable visual angle measured in minutes)
  • VISUAL AXIS – The main line of sight which extends from the fovea to the object of regard
  • VISUAL BEHAVIOR PATTERN – It is made up of the behavior patterns of convergence and accommodation, the other skeletal postural patterns and the other contributory visceral patterns
  • VISUAL GRASP – The ability to hold the eyes fixed on an object
  • VISUAL PROBLEM – A visual pattern which has suffered a decrement in performance (It is a distorted response, a distortion in the manipulation of visual space.)
  • VISUAL SPACE – The external world as perceived through the eyes
  • VISUALIZATION – The skill of localizing and identifying objects from which there is no immediate visual input
  • VISUALIZE – The ability to remember, know and predict where and what things were, are and will be in space-time
  • VITREOUS – The transparent fluid which helps hold the shape of the inner eye
  • Additional terms and explanations can be found on the Children with Special Needs Website.