Vision Screening Online Training Program

Glossary of Vision Screening Terms

Accommodation – The adjustment of the eye for seeing at different distances, accomplished by changing the shape of the crystalline lens through action of the ciliary muscle, thus focusing a clear image on the retina.

Amblyopia – Optically uncorrectable blurred vision due to disuse of the eye.

Anterior Chamber – Space in the anterior portion of the eye; bounded in front by the cornea and behind by the iris; filled with aqueous fluid.

Aqueous Humor – A water-like fluid, which fills the anterior chambers of the eye, manufactured by the ciliary body.

Astigmatism - A defect of curvature of the refractive surface of the eye the result of which a ray of light is not sharply focused on the retina but is spread over a more or less diffused area.  This results in the formation of a distorted image.

Binocular Vision – The ability to use both eyes simultaneously to focus on the same object and to fuse the two images into a single image which gives a correct interpretation of its solidity and its position in space.

Blepharitis – Inflammation of the margin of the eyelids.  Sometimes referred to as granulated eyelids.

Blindness – In the United States, the legal definition of blindness is: central visual acuity of 20/200 or less in the better eye after correction.

Choroid – The choroid is the intermediate layer of the coat of the eyeball and lies between the retina and the sclera.  It contains blood vessels, which provides nourishment and cooling to the retina.

Cataract – A condition in which the crystalline lens of the eye, or its capsule, or both become opaque, with consequent loss of visual acuity.

Cilia – Eyelashes

Ciliary Body – Portion of the vascular coat between the iris and the choroid that produces the aqueous humor.  It consists of ciliary processes and the ciliary muscle.  This organ changes the convexity of the lens when a change of Accommodation is required.

Color Deficiency – Inability to perceive differences in color, usually for red or green, rarely for blue or yellow.  Condition exists in varying degrees from minor loss to complete color blindness.  It affects approximately 7% of males and 0.1% of females.

Concave Lens - Lens having the power to diverge parallel rays of light; also known as diverging, reducing, negative, myopic or minus lens, denoted by the sign (-).

Cones – One of the two types of light-sensitive cells that are scattered over the surface of the retina, making it possible to transmit visual impulses to the brain.  Cones see fine detail and color and are more numerous at the back of the eye in the region of the macula.

Conjunctiva – Mucous membrane, which lines the eyelids and covers the front part of the eyeball, and the surface of the sclera. 

Conjunctivitis:  Inflammation of the conjunctiva.

1.) Acute bacterial conjunctivitis (pink eye)
This type of conjunctivitis is highly contagious and often is caused by gram-positive organisms (staphylococcus, Haemophilus, Proteus), although other bacteria may be involved.  The onset is acute, characterized by mucopurulent drainage from one or both eyes.  Preventing spread of the organism with meticulous hand washing and use of separate towels is important.  The disease frequently is self-limiting and resolves spontaneously in 10 to 14 days.  Antibiotic eye drops usually are effective.       

2.) Viral conjunctivitis
This type of conjunctivitis is caused by an adenovirus.  Symptoms vary from mile to severe.  Some strains of virus cause conjunctivitis and pharyngitis (phaaryngoconjunctival fever), and other causes keratoconjunctivitis.  Both types are contagious, with watering, redness, and photophobia.  Treatment is symptomatic.

3.) Allergic Conjunctivitis
This is associated with a variety of antigens, including pollens.  There is ocular itching associated with photophobia, burning, and gritty sensations in the eye.  Treatment is symptomatic and may include antihistamines, steroids, and vasoconstrictors.

Convergence – The process of directing the visual axes of the two eyes to a near point, with the result that the pupils of the two eyes are closer together.  The eyes are turned inward toward the nose.

Convex Lens – Lens having power to converge parallel rays of light and to bring them to a focus; also know as converging, magnifying, hyperopic, or plus lens, denoted by the sign (+).  (See Plus Sphere Lens)

Cornea – The anterior transparent portion of the outer coat of the eye through which light enters.

Crystalline Lens – A transparent, colorless body suspended in the anterior portion of the eyeball, between the aqueous and vitreous chambers, the function of which is to help bring the rays of light to a focus.

Depth Perception – The ability to perceive the solidity of objects and their relative position in space.  Syn. Stereoscopic vision.

Diopter – A unit of measurement denoting the amount a lens can bend a light ray at a distance of one meter.  A term used to describe the strength of a lens.

Diplopia – Double vision.

Emmetropia – Absence of refractive error.

Epicanthus – An anatomical feature in which a fold of skin extending from the top of the nose to the inner end of the eyebrow overlaps the inner corner of the eye; in some circumstances can give the appearance of strabismus; tends to recede as the bridge of the nose narrows in the course of early childhood.

Esophoria – A tendency of the eye to turn inward.

Esotropia - A manifest of observable turning inward of the eye (convergent strabismus or crossed eye).

Exophoria – A tendency of the eye to turn outward.

Exophthalmos – A condition in which the eyeballs protrude or bulge abnormally from their sockets.

Exotropia – A manifest of observable turning outward of the eye (divergent, strabismus or wall eye).

Field of Vision – The entire area, which can be seen at one time without shifting the head or eyes.

Floaters – The perception of small particles or objects floating in front of the eye by an individual due to changes in the structure of vitreous, or to cells or material floating in the vitreous.

Focus – Point at which rays are converged after passing through a refractive substance.  Focal distance is the distance rays travel after refraction before focus is reached.

Fovea – Small depression in the retina at the back of the eye; the part of the macula adapted for the most acute vision (central vision).

Fundus – The inner surface of the posterior part of the eye.

Fusion – Coordination of the images seen by each eye individually into one picture.

Glaucoma – Disease of the eye marked by increased intraocular pressure resulting in hardness of the eyeball; can cause blindness if not treated adequately.

Granulated Lids – Particles of matter gathered on the eyelids.  A severe case would completely surround the lids and considerable redness and inflammation would be present.

Hyperopia–Far Sightedness – A refractive error in which the eyeball is too short from front to back or the refractive power of the eye too weak, so that parallel rays of light are brought to a focus behind the retina.  The condition requires a convex (plus) lens to correct.

Hypertropia – A tendency of one eye to deviate upward.

Iris – The part of the eyelid, which gives it color.  Circular membrane, which regulates the amount of light entering the eye by changing the size of the pupil.

Lacrimal Apparatus – The system responsible for the formation, secretion, and drainage of tears.  Includes: lacrimal canal; lacrimal duct; lacrimal fluid (tears); lacrimal gland.

Lazy Eye – Lay term for amblyopia.

Lens – A transparent, flexible body, convex on both surfaces and lying directly behind the iris of the eye; serves to focus light rays on the retina. 

Leukocoria – The presence of a white pupillary reflex.  This can be the presenting result of several diseases including congenital cataracts or retinoblastoma.

Monocular – Pertaining to or having one eye.

Myopia–Near Sightedness – A refractive error in which the eyeball is too long or the refractive power too strong, so that parallel rays of light are focused in front of the retina.  The condition requires a concave (minus) lens to correct. 

Near Point of Accommodation – The nearest point at which the eye can see an object distinctly.  It varies according to the power of accommodation in the individual. 

Near Point of Convergence – The nearest point at which the two eyes can direct their gaze simultaneously, normally about three inches from the nose.

Night Blindness – A condition in which the sight is good by day but deficient at night or in faint light.  

Nystagmus – An involuntary, rapid movement of the eyeball; it may be lateral, vertical, rotary, or mixed.

Occlude – To cover one eye.

Oculus Dexter (O.D.) – Right eye.

Oculus Sinister (O.S.) – Left eye.

Oculus Uterque (O.U.) – Both eyes.

Ophthalmologist – A licensed physician – M.D. – who specializes in diagnosis and treatment of defects and diseases of the eye, performing surgery when necessary or prescribing other types of treatment, including glasses, contact lenses and optical aids.

Ophthalmoscope – An instrument used in examining the interior of the eye.

Optician – One who grinds lenses, fits then into frames, and adjusts the frames to the wearer.

Optic Nerve – Second cranial nerve; the special nerve of the sense of sight, which carries messages from the retina to the visual centers in the brain.

Orthophoria – Straight eyes.

Orthoptics – The technique dealing with the diagnosis of muscle and sensory imbalances and the therapy necessary to re-educate and restore sensory and motor coordination.

Optometrist – A licensed specialist in vision.  An O.D. specializing in the examination of the eyes, prescribing glasses, contact lenses, optical aids, and services for enhancement of vision.

Peripheral Vision – Ability to perceive presence, motion, or color of objects outside of the direct line of vision.

Phoria – A root word denoting a latent deviation in which the eyes have a tendency to turn from the normal position, used with a prefix to indicate the direction of such deviation (hyperphoria, up; esophoria, in; exophoria, out).

Photophobia – Abnormal sensitivity to and discomfort from light.

Posterior Chamber – Space between the posterior surface of the iris and the anterior surface of the lens; filled with aqueous fluid.

Presbyopia – Physiological aging change in the eye characterized by lessening of the elasticity of the lens and weakening of the ciliary muscle.  These changes result in an inability to focus on near objects.

Ptosis – Drooping of the eyelid, which if significant, may interfere with vision.

Pupil – The opening at the center (appears dark) of the iris of the eye for the transmission of light.

Refraction – Determination of refractive errors of the eye and correction by glasses.

Retina – The innermost layer of the coat of the eyeball that lies next to the vitreous.  It is formed of highly specialized and sensitive cells, the “rods” and “cones” that transmit messages to the optic nerve when they are stimulated by light.

Retinal Detachment – Separation of the retina from back of the eye.

Retinitis – Inflammation of the retina.

Retinitis Pigmentosa – A chronic, progressive degeneration (usually hereditary) consisting of atrophy of the retina with characteristic deposits of pigment.

Rods – One of the two types of light sensitive cells that are scattered over the surface of the retina, making it possible to transmit visual impulses to the brain.  Rods perceive dim light and are not color sensitive.

Sclera – The white part of the eye.  A tough covering which, with the cornea, forms the external, protective coat of the eye.

Snellen Chart – Used for testing central visual acuity.  It consists of lines, letters, numbers, or symbols in graded sizes drawn to Snellen measurements.  Each size is labeled with the distance at which it can read by the normal eye; most often used in testing vision at distance of 10 or 20 feet.

Stereoscopic – See binocular vision.

Stereopsis – Depth perception.

Strabismus – Failure of the two eyes to simultaneously direct their gaze at the same object because of muscle imbalance, synonymous with tropia.

Sty (Stye) ( Hordeolum) – Acute inflammation of sebaceous gland in the margin of the eyelid, due to infection and usually resulting in the formation of a pus sac.

Suppression – The condition in which sensations from one eye are involuntarily and unconsciously ignored, or “suppressed”, by the nervous system.  When strabismus is present, suppression prevents the double vision, which would otherwise occur due to the misalignment of the eyes.  Suppression over a period of time interferes with development of the eye and the development of normal binocular vision. (See Amblyopia).

Tropia – A root word denoting a manifest or observable deviation from normal of the axis of the eyes (strabismus).  Used with a prefix to denote the type of strabismus, as heterotopias, esotropia, exotropia.

Visual Acuity – Sharpness of vision with respect to ability of the eye to distinguish detail as an object is placed farther away or as it becomes smaller in size.

Vitreous Humor – The transparent jellylike substance, which fills the major part of the eyeball and holds it spherical.