Superior Vision - Vision Care Learning Center

20/20 Vision:

The expression for normal vision. This notation is expressed as a fraction. The numerator (1st number) refers to the distance you were from the test chart, which is usually 20 feet (6 meters). The denominator (2nd number) denotes the distance at which a person with normal eyesight could read the line with the smallest letters that you could correctly read. For example, if your visual acuity is 20/100 that means that the line you correctly read at 20 feet could be read by a person with normal vision at 100 feet. The Snellen chart, which consists of letters, numbers, or symbols, is used to test visual acuity (sharpness of eyesight). A refraction test is used to determine the amount of correction needed for a prescription when treating refractive error such as astigmatism, myopia, or hyperopia.

Accommodation:

Increase in focusing power of the eye to maintain a clear image as objects are moved closer. Due to the crystalline lens becoming less flexible as age increases, the result is a natural loss of accommodation (focusing power). This condition is called presbyopia.

Acuity:

Clearness of eyesight. The amount of acuity depends on the sharpness of images and the sensitivity of nerve elements in the retina.

Add:

Prescription strength of a plus lens which is used for near vision. A plus lens can be added to another lens such as a minus lens for distance vision.

Age-related macular degeneration or disease (AMD, ARMD):

Deterioration of the macula affecting people older than 60, resulting in loss of sharp central vision. This is the leading cause of legal blindness in the United States.

Amblyopia or "lazy eye":

Decreased vision in one or both eyes without detectable anatomic damage to the retina or visual pathways. If detected early in life, this condition may be correctable by eyeglasses or contact lenses.

Aqueous or aqueous humor or aqueous fluid:

Clear, watery fluid that fills the anterior and posterior chambers of the eye. Nourishes the cornea, iris, and lens and maintains intraocular pressure.

Astigmatism:

A type of refractive error. Optical defect in which refractive power of an eye is not uniform in all directions (meridians). A large amount may result in headache and significant blurring of images. This condition is typically correctible through a cylindrical power included into the lens design.

Axis:

The alignment of the len's cylindrical part; used for correcting astigmatism. This measurement is given in degrees. The values are typically from 90 degrees to 180 degrees.

Bifocals:

Eyeglass lenses that incorporate two different refractive powers in each lens, usually for near and distance corrections.

Binocular vision:

Blending, by the brain, of the separate images seen by each eye into one composite image. Also, explained as the simultaneous use of the two eyes.

Blind spot:

Sightless area within the visual field of a normal eye. Caused by absence of light-sensitive photoreceptors where the optic nerve enters the eye.

Cataracts:

Opacity or cloudiness of the crystalline lens, which may prevent a clear image from forming on the retina. Surgical removal of the lens is necessary if visual loss becomes significant, with lost optical power replaced with an intraocular lens.

Cataract extraction:

Removal of a cloudy lens from the eye. Extracapsular cataract extraction leaves the rear lens capsule intact; with an intracapsular extraction (usually by cryoextraction) there is complete removal of the lens with its capsule.

Color blindness:

Reduced ability to discriminate among colors, especially shades of red and green. Usually hereditary; much more common in men.

Conjunctiva:

Transparent mucous membrane covering the outer surface of the eyeball except the cornea, and lining the inner surfaces of the eyelids.

Cornea:

Transparent, dome-shaped front part of the eye that covers the iris, pupil, and anterior chamber and provides most of an eye's optical power.

Corneal disease:

Group of infections, dystrophies, and injuries affecting the cornea.

Cross-eyes:

See esotropia.

Crystalline lens:

See lens.

Diabetic retinopathy:

Retinal changes accompanying long-standing diabetes mellitus. Early stage is background retinopathy. May advance to proliferative retinopathy, which includes the growth of abnormal new blood vessels (neovascularization). Leading cause of visual impairment among working-age Americans. Diabetes also can cause cataracts.

Dilated pupil:

Enlarged pupil, resulting from contraction of the dilator muscle or relaxation of the iris sphincter. Occurs normally in dim illumination, or may be produced by eye-drops containing drugs (mydriatics) during an eye exam.

Diopter:

Unit designating the refractive power of a lens.

Diplopia, double vision:

Perception of two images from one object.

Dry eye syndrome or dry eye:

Corneal and conjunctival dryness due to deficient tear production, predominantly in older women. Can cause foreign body sensation, burning eyes, and erosion of conjunctival and corneal epithelium.

Elective Contact Lenses:

This refers to contact lenses that are worn primarily for cosmetic purposes. The lens wearer does not have one of the conditions described as Medically Necessary Contact Lenses.

Emmetropia:

Refractive state of having no refractive error. Images of distant objects are focused sharply on the retina without the need for either accommodation or corrective lenses.

Esotropia, cross-eyes:

Eye misalignment in which one eye turns inward (toward nose) while the other fixates normally.

Eximer laser:

Class of ultraviolet lasers that removes tissue accurately without heating it. In refractive surgery, controlled by computer to make precise pre-programmed shavings of eye tissue to produce a given optical correction.

Exotropia, wall-eyes:

Eye misalignment in which one eye turns outward (away from nose) while the other fixates normally.

Extraocular muscles:

Six muscles that move the eyeball.

Farsightedness:

See hyperopia.

Floaters:

Particles that float in the vitreous and cast shadows on the retina; seen as spots, cobwebs, spiders, etc. Occur normally in aging and with vitreous detachment, but also pathologically in retinal tears and inflammation.

Fovea:

Central pit in the macula that produces sharpest vision. Contains a high concentration of cones and no retinal blood vessels.

Glaucoma:

Group of diseases, usually characterized by increased intraocular pressure, resulting in damage to the optic nerve. A common cause of preventable vision loss. Leading cause of blindness among black Americans. May be treated by prescription drugs or surgery.

High Index Lenses:

A form of lens material that allows the lens to be made thinner than with standard glass or plastic materials.

Hyperopia, farsightedness:

Type of refractive error. Focusing defect in which an eye is underpowered; light rays coming from a distant object strike the retina before coming to sharp focus, blurring vision. Corrected with additional optical power, which may be supplied by a plus lens (spectacle or contact).

IOL:

Plastic lens that may be implanted during cataract surgery to replace the eye's natural lens.

Intraocular pressure:

Fluid pressure inside the eye. Measured with a tonometer. The pressure is usually abnormally high in Glaucoma.

Iris:

Pigmented tissue lying behind the cornea that gives color to the eye (e.g. blue eyes) and controls amount of light entering the eye by varying the size of the pupillary opening.

Keratoconus:

Degenerative, hereditary corneal disease affecting vision. Characterized by generalized thinning and cone-shaped protrusion of the central cornea, usually in both eyes.

Laser:

Acronym for Light Amplification by Stimulated Emission of Radiation. High energy light source to cut, burn, or dissolve tissues for various clinical purposes: in the retina, to treat diabetic retinopathy and macular degeneration by destroying leaking and new blood vessels (neovascularization); on the iris or trabecular meshwork, to decrease pressure in glaucoma; after extracapsular cataract extraction, to open the posterior lens capsule.

LASIK:

Acronym for Laser in Situ Keratomileusis. Type of refractive surgery in which the cornea is reshaped to change its optical power. A disc of cornea is raised as a flap, then an excimer laser is used to reshape the middle layer of corneal tissue, producing surgical flattening. Used for correcting myopia, hyperopia, and astigmatism.

Lazy eye:

See amblyopia.

Lens, crystalline lens:

The eye's natural lens. Transparent, biconvex-shaped tissue that helps bring rays of light to a focus on the retina.

Lenticular Lenses (plus):

Prior to the use of surgical implant lenses after cataract removal, the lenticular lens was used in eyeglasses to offset the visual effect of having no lens behind the pupil to focus on objects both near and far. To do this a "high plus" trifocal eyeglass lens of approximately 10 to 15 diopters was required. A "high plus" lens is a lens that is very thick in the center and thin at the edges.

Lenticular Lenses (minus):

"High minus" lenticular lenses, although still available today as a benefit, are also not often used. A "high minus" lenticular lens is a lens that is very thick at the edges and very thin in the center. The lens design is used for those who typically must wear prescriptions of approximately minus10 diopters and higher. The "high minus" lenticular lens makes the eye of the wearer, from an observer's stand point, appear to be about twice as small as actual. The lens has the appearance of being "dished-out" in the center. The minus lenticular lens design has for all intents and purposes been replaced by lenses made of "high index" materials.

Low vision:

Term usually used to indicate vision of less than 20/20.

Low vision aids:

Instruments such as magnifiers, prisms, print and audio materials, and computer programs to allow people with low vision to read and perform other tasks. Help is available even for people who have lost much of their vision.

Macula:

Small central area of the retina surrounding the fovea; area of well-resolved, acute central vision.

Macular degeneration:

Retinal diseases in which central vision is lost. Age-related type (AMD) or age related macular degeneration is very common and affects people over 60. Juvenile macular diseases are hereditary; they include Stargardt's disease and Best's vitelliform macular dystrophy.

Medically Necessary Contact Lenses:

Medically Necessary contact lenses are provided only under certain medical conditions. These medical conditions prevent the member from achieving a specified level of visual acuity (performance) through the wearing of conventional eyeglasses. These contact lenses must be specifically prescribed by the eye doctor to be used for the reason or reasons described below. Reimbursement for these lenses will be considered as payment-in-full when utilizing a network provider.

Aphakia. A pair of prescription single vision or multifocal eyeglass lenses and an eyeframe can be provided along with contact lenses prescribed for this reason.
When visual acuity cannot be corrected to 20/70 in the better eye except through the use of contact lenses (must be 20/60 or better).
Anisometropia of 4.0 diopters or more, provided visual acuity (performance) improves to 20/60 or better in the weak eye.
Keratoconus. The narrowing of visual fields due to high minus or plus corrections is not considered a reason for medically necessary contact lenses. All requests for medically necessary contact lenses must be reviewed and approved by the Medical Advisory Board.

Minus (-) Lens:

Concave lens, stimulates focusing and diverges light. The lens is thinner in the center than the edges. It is used in glasses or contact lenses for people who are nearsighted (myopia).

Myopia, nearsightedness:

Focusing defect in which the eye has too much optical power. Light rays coming from a distant object are brought into focus before reaching the retina. Requires a minus lens correction to "weaken" the eye optically and permit distance vision.

Nearsightedness:

See Myopia.

Ophthalmologist:

Physician (MD) specializing in diagnosis and treatment of refractive, medical and surgical problems related to eye diseases and disorders.

Ophthalmoscope:

Diagnostic instrument that allows the doctor to view the retina.

Optician:

Professional who makes and adjusts optical aids, e.g., eyeglass lenses, from refraction prescriptions supplied by an ophthalmologist or optometrist. The optician may also fit contact lenses in some states.

Optic nerve:

Largest sensory nerve of the eye; carries impulses for sight from the retina to the brain.

Optometrist:

Doctor of optometry (OD) specializing in vision problems, treating vision conditions with spectacles, contact lenses, low vision aids and vision therapy as well as prescribing medications for certain eye diseases.

Oversize Lenses:

When the length (boxed) of an eyeglass lens is larger than 60mm.

Peripheral vision:

Side vision; vision elicited by stimuli falling on retinal areas distant from the macula. Images are not well resolved.

Photochromic Lenses:

Lenses containing material that is photosensitive to ultraviolet light rays. Exposure to ultraviolet darkens the lens color. Conversely, a lack of ultraviolet rays will allow the lens to lighten in color.

Photophobia:

Abnormal sensitivity to, and discomfort from light which may be associated with excessive tearing. This is a condition, that is often due to inflammation of the iris or cornea.

Plano Lens:

a lens that has no prescription. No variance between the curvature of the front and back lens surfaces.

Plus (+) Lens:

convex lens (thicker in the middle) relaxes focusing and converges light. It is typically used in glasses or contact lenses for people who are farsighted (hyperopic). It may also be prescribed for other visual conditions as well.

Polaroid Lens:

a lens used in sunglasses and sometimes 3D glasses which consists of two glass or plastic surfaces with a plastic lamination between the two surfaces, and designed to reduce reflected glare.

Polycarbonate Lenses:

A plastic-like material used in eyeglass lenses that, because of its inherent softness, will not shatter or break in the same way that glass and other plastic materials may.

Presbyopia:

Refractive condition in which there is a diminished ability to accommodate (focus) arising from loss of elasticity of the crystalline lens, as occurs with aging. Usually becomes significant after age 45.

PRK (photorefractive keratectomy):

Use of high intensity laser (e.g., an excimer laser) to reshape the corneal curvature; for correcting refractive errors.

Prism:

a wedge-shaped lens which is thicker on one edge than the other. This plastic or glass lens bends light (opposite direction from its thicker end). Prisms can be used to measure an eye misalignment and/or treat a binocular dysfunction (eye teaming problem). A prism is sometimes added to glasses to help improve eyesight due to an eye misalignment or visual field loss.

Progressive addition lens (PAL), progressive power lens:

Eyeglass lenses that incorporate corrections for distance vision, through midrange to near vision (usually in lower part of lens), with smooth transitions and no bifocal demarcation line. Also, known as "no-line" multi-focal lenses.

Pupil:

Variable-sized, circular opening in the center of the iris that regulates the amount of light entering the eye. Appears black when looking at the eye.

Radial keratotomy (RK):

Type of refractive surgical procedure. Series of spoke-like (radial) cuts made in the cornea to flatten it, reducing its refractive power and thereby correcting myopia (nearsightedness). Now, mostly replaced by LASIK.

Refraction:

A test performed by optometrist or ophthalmologist to determine an eye's refractive error and the best corrective lenses to be prescribed. Series of lenses in graded powers are used to determine which provide sharpest, clearest vision.

Refractive error:

Optical defect in an eye. Parallel light rays are not brought to a sharp focus precisely on the retina, producing a blurred retinal image. Can be corrected by eyeglasses (spectacles), contact lenses, or refractive surgery.

Retina:

The innermost layer of the eye, a neurological tissue, which receives light rays focused on it by the lens. This tissue contains receptor cells (rods and cones) that send electrical impulses to the brain via the optic nerve when the light rays are present.

Retinitis pigmentosa (RP):

Set of inherited retinal degenerations. Death of photoreceptors gradually leads to night-blindness and loss of peripheral vision causing tunnel vision.

Sclera:

Opaque, fibrous, protective outer layer f the eye (white of the eye) that is directly continuous with the cornea in front and with the sheath covering optic nerve behind.

Single Vision:

A lens that has one sphere power and/or one cylindrical power.

Slit lamp:

Microscope used for examining the eye; allows cornea, lens and otherwise clear fluids and membranes to be seen in layer-by-layer detail.

Snellen chart:

Test chart used for assessing visual acuity. Contains rows of letters, numbers, or symbols in standardized graded sizes, with a designated distance at which each row should be legible to a normal eye. Usually tested at a distance of 20 feet.

Strabismus:

Eye misalignment caused by extraocular muscle imbalance; one fovea is not directed at the same place in a scene as the other. This is usually corrected through the use of prisms.

Standard Lenses:

Lenses that are made of either tempered glass or CR-39 plastic manomer. Standard lenses are typically not coated or tinted.

Tonometer:

An instrument used to measure intraocular pressure.

Trifocal:

Eyeglass lens that incorporates three lenses of different powers. The main portion is usually focused for distance (20 feet), the center segment for about 2 feet, and the lower segment for near vision (14 in).

Visual acuity:

Assessment of the eye's ability to distinguish object details and shape using the smallest identifiable object that can be seen at a specified distance (usually 20 feet).

Visual field:

Full extent of the area visible to an eye that is fixating straight ahead.

Vitreous or vitreous humor or vitreous body:

Transparent, colorless, gelatinous mass that fills the rear two-thirds of the eyeball between the lens and the retna.

Wall-eyes:

See extropia.

Glossary