Vision Screening Resources and Glossary

Glossary

Accommodation - the adjustment of the lens to focus at different distances through action of the ciliary muscle

Amblyopia - poor vision in one or both eyes not due to organic defect

Anisometropia - inequality in the refractive power of the two eyes of considerable degree

Anterior chamber - the space between the cornea and the iris

Aqueous humor - the clear fluid which fills the anterior and posterior chambers of the eye

Astigmatism - a refractive error in which a defect of curvature on one of the refractive surfaces of the eye prevents a clear image from being focused on the retina

Binocular vision - the ability to use both eyes simultaneously to focus on the same object and fuse the two images into one with the correct interpretation of solidity and position in space

Blepharitis - inflammation of the glands and lash follicles along the margin of the eyelids

Blindness - legal blindness is a visual acuity of 20/200 and or the ability to see only 20% or less of the visual field after best correction in the better eye

Blind spot - area where retinal nerve fibers converge (optic disc) to form the optic nerve. Corresponds to the area of non-vision in the visual field

Cataract - a defect in the transparency or opacity of the lens or its capsule

Chalazion - a lump on the eyelid that results from chronic inflammation of meibomian gland

Choroid - the vascular layer located between the sclera and the retina

Cilia - of the eye refers to eyelashes

Ciliary body - the portion of the uveal tract between the iris and the choroid that contains the muscles of accommodation and secretes aqueous

Coloboma - absence or defect of some ocular tissue, usually a congenital fissure of any part of the eye, such as an incomplete iris

Color deficiency - inability to perceive differences in color, usually for red-green, rarely for blue-yellow. It can range from mild to severe in degree. It is more common in males than females

Concave lens - a lens having the power to diverge parallel rays of light. It is used to correct myopia

Cones - one of two types of light-sensitive cells on the retina. Cones are more numerous in the area of the macula and are responsible for seeing color and fine detail

Conjunctiva - delicate membrane that lines the eyelids and the exposed part of the sclera

Conjunctivitis - inflammation of the conjunctiva

Convergence - simultaneous turning of the eyes toward each other

Convex lens - a lens having the power to converge parallel light rays to bring an image to focus. It is used to correct hyperopia or presbyopia

Cornea - the clear transparent membrane that covers the iris and pupil and joins the conjunctiva

Crystalline lens - a transparent colorless body suspended in the anterior portion of the eyeball between the aqueous and vitreous chambers. Its function is to help bring light rays into focus.

Dacryocystitis - inflammation of the tear sac, usually due to blockage

Depth perception - the ability to perceive the solidity of objects and their relative position in space. Stereopsis

Diopter - unit of measurement expressing the strength or refractive power of a lens at one meter

Diplopia - double vision

Divergence - simultaneous turning of the eyes away from each other

Emmetropia - absence of refractive error

Epicanthus - congenital skin fold overlying the inner portion of the upper lid and the inner canthus; simulates the appearance of esotropia. Tends to recede as the bridge of the nose narrows in early childhood

Esophoria - a latent tendency of the eye to turn inward

Esotropia - a manifest inward deviation of the eye

Exophoria - a latent tendency of the eye to turn outward

Exotropia - a manifest outward deviation of the eye

Farsightedness - a lay term for hyperopia

Field of Vision - the entire area which can be seen at one time without shifting the head or eyes

Floaters - opacities within the vitreous space that cast moving shadows on the retina

Focus - adjustment of the lens to produce a clear picture

Fovea - small depression in the retina at the back of the eye; part of the macula adapted for the most acute vision

Fusion - the integration of two separate images into a single mental picture

Glaucoma - a disease marked by increased intra-ocular pressure, which can cause blindness if not treated

Hyperopia - the refractive condition of the eye at rest such that light rays from a distant object are focused behind the retina

Hypertropia - a tendency of one eye to deviate upward

Iris - the colored circular membrane surrounding the pupil

Iritis - inflammation of the iris

Lacrimal apparatus - the system responsible for the formation, secretion, and drainage of tears

Lazy eye - lay term for amblyopia

Lens - the transparent body, convex on both surfaces, lying directly behind the iris and serves to focus light rays on the retina

Lids - the outermost covering of the eye

Macula - a small depressed area in the retina where sharpest vision occurs

Monocular - pertaining to or having one eye

Myopia - a refractive error in which the eyeball is too long from front to back or the refractive power so strong so that parallel rays of light are focused in front of the retina

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 two eyes can direct their gaze simultaneously, normally about three inches from the nose

Nearsighted - lay term for myopia

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

Occluder - a device used to cover one eye during vision screening

Oculus dexter (O.D.) - right eye

Oculus sinister (O.S.) - left eye

Oculi uterque (O.U.) - both eyes

Ophthalmologist - an MD who specializes in medical and surgical diagnosis and treatment of defects and diseases of the eye, prescribes drugs, eyeglasses, contact lenses and optical aids

Ophthalmoscope - an instrument used in examining the interior of the eye

Optic nerve - nerve by which visual impulses are transmitted from the retina to the brain

Optician - a person who grinds lenses, fits them into frames, and adjusts the frames to the wearer

Optometrist (OD) - a doctor of optometry who specializes in the diagnosis and treatment of functional vision problems, prescribes correctives lenses, contact lenses, or visual therapy and examines for eye disease or ocular signs of systemic disease

Orthophoria - straight eyes

Peripheral vision - ability to perceive presence, motion or color of objects to the side

Phoria - a root word denoting a latent tendency of one eye to deviate up, down, left or right

Photophobia - eyes having an abnormal sensitivity or discomfort in light

Plus lens - a convex lens used for screening farsightedness by checking the eyes' ability to accommodate at distance

Posterior chamber - space between the posterior surface of the iris and anterior surface of the lens filled with aqueous fluid

Presbyopia - physiological change in the eye characterized by the lens becoming less elastic and therefore not able to focus up close

Ptosis - drooping of the upper eyelid

Pupil - the opening at the center of the iris that adjusts to allow light to enter the eye

Refraction - determination of refractive errors of the eye and correction by glasses

Retina - the innermost light sensitive layer of the eye; contains the rods and cones

Rods - vision cells that are not color sensitive; used for perception of motion, in low illumination, and in night vision

Sclera - the white part of the eye, which with the cornea, forms the external protective coat of the eye

Stereopsis - binocular depth perception

Strabismus - eyes that are out of alignment

Sty - infection of a gland in the margin of the eyelid

Suppression - a condition in which the image from one eye is ignored (suppressed) by the brain. Suppression that exists for a period of time could lead to amblyopia

Tropia - a root word denoting a manifest turning in, out, up or down of one eye in relation the other

Uvea - vascular and pigmented layer of the eye, includes the choroid, ciliary body and the iris

Visual acuity - the ability of the eye to distinguish detail as an object is placed farther away or as it becomes smaller in size

Vitreous humor - transparent gelatinous substance that fills the space behind the lens and keeps the eyeball expanded and in shape