The index allows you to select a word from the list and go directly to it's definition or a more detailed description on this website. You can also jump to related items. The definitions follows this quick index guide.

ACCOMMODATION:

The ability of the eye to change its focus from distant to near objects. The process is achieved by the lens changing its shape.

ACUITY:

The level or degree of sense perception.

ANIRIDIA:

The iris surrounds the pupil and regulates how much light is allowed to enter into the inner eye. The size of the pupil is altered by the iris during normal operations. When the iris is damaged or missing, the pupil cannot be adjusted properly. This condition is Aniridia. Aniridia is normally caused by an eye injury (Traumatic Aniridia) or as a birth defect (Congenital Aniridia). It is not a condition which develops during a persons lifetime.

ANTERIOR CHAMBER: DETAIL

The space in front of the iris and behind the cornea.

AQUEOUS HUMOR, AQUEOUS FLUID: DETAIL

Clear, watery fluid that flows between and nourishes the lens and the cornea; secreted by the ciliary processes.

ASTIGMATISM: DETAIL

A condition in which the surface of the cornea is not spherical, which causes a distorted image to be received at the retina. A normal cornea is shaped like a perfect hemisphere (half circle) which allows the eye to focus all of the incoming light rays onto the retina. Astigmatism is an abnormally shaped cornea which causes the focal point of some light rays to be off of (either in front or behind) the retina while others are focused on the retina. This condition often results in a slightly blurred picture for mild cases and increasingly blurred picture in more severe cases. Most astigmatic conditions develop during the growth years and will not advance later in life.

AVERAGE:

This website refers to average as the vision which a majority of people have during their normal periods. Related: Normal

BINOCULAR FUSION:

Both eyes being able to move in unison (as instructed by the brain) and for the brain to be able to merge (fuse) both eye images into one total interpreted picture.

BINOCULAR RATINGS:

Binoculars and some visual aids are marked with specifications similar to 8x21. In this example, 8 is the power magnification and 21 is the size of the front lens in millimeters. The size of the lens determines the angle (or range) of view, with bigger lens sizes yielding a wider view angle.

BINOCULAR VISION:

The blending of the separate images seen by each eye into a single image. Allows images to be seen with depth.

BIOMICROSCOPE: DETAIL

A high powered magnification unit with a vertical beam of light which enables the doctor to see detail of the inner eye.

BLEPHARITIS:

Inflammation of the eyelids. This is very common.

BLIND: DETAIL

Having no meaningful sight. Related: Legally blind

BLIND:

Blinking is a rapid closure and reopening of eyelids.

BLIND SPOT:

A small area where the optic nerve enters the eye causes a gap in the visual field corresponding to this area where no visual cells are present. It occurs normally in all eyes. Can also mean any gap in the visual field.

BLINK: DETAIL

The process when the eyelids close and open again rapidly. This is how the eye cleans itself. The eyelids help to disperse the tear fluid over the surface of the conjuntiva.

CATARACT: DETAIL

A cataract is a situation where the normally opaque eye lens becomes cloudy, has impurities within it, or becomes compressed. This blocks the light rays from traveling through the lens to the retina and causes blank patches to appear in the picture.

CENTRAL RETINAL ARTERY:

The blood vessel that carries blood into the retina.

CENTRAL RETINAL VEIN:

The blood vessel that carries blood from the retina.

CHORIORETINITIS:

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CHOROID:

The layer filled with blood vessels that nourishes the retina; part of the uvea.

CILIARY MUSCLES:

The muscles that relax the zonules to enable the lens to change shape for focusing.

CILIARY PROCESSES:

The extensions or projections of the ciliary body that secrete aqueous fluid.

CONES, CONE CELLS: DETAIL

One type of specialized light-sensitive cells (photoreceptors) in the retina that provide sharp central vision and color vision. Related: RODS.

CONGENITAL:

In existence from the moment of birth. Also can mean started during fetal development rather than from heredity.

CONJUNCTIVA: DETAIL

The thin, moist tissue (membrane) that lines the inner surfaces of the eyelids and the outer surface of the sclera.

CONTRAST SENSITIVITY:

The ability to perceive differences between an object and the background.

CONVERGENCE: DETAIL

The act of both eyes turning in (toward each other) slightly in order to obtain a common focus on objects.

CORNEA: DETAIL

The outer, transparent, dome-like structure that covers the iris, pupil, and anterior chamber; part of eye's focusing system.

DEPTH PERCEPTION: DETAIL

The ability to see depth of objects. Seeing three dimensionally rather than two dimensionally.

DILATION:

Temporary enlargement of the pupil with special eye drops (mydriatic) which allows the eye care specialist to better view the inside of the eye.

DIOPTER: DETAIL

This is the measurement of refractive strength of a lens.

DIVERGENCE:

The act of both eyes turning out (away from each other).

DOUBLE VISION:

Seeing a single object as two very close twins (called 'ghosting') indicates a problem with the ability to merge the images transmitted by both eyes into one common image. Related: BINOCULAR FUSION.

DRUSEN:

Tiny yellow or white deposits in the retina or optic nerve head.

EMMETROPIA:

The term for the normal refractive ability to bring parallel light rays to a common focal point upon the retina, having no refractive error.

EPISCLERITIS: DETAIL

Sensitivity reaction where the eye becomes red in one area. Associated with rigid or soft contact lenses.

FLOATER: DETAIL

Cells from the lining of the eyeball can detach and then 'float' in the normally transparent vitreous fluid of the eye. These non-transparent cells block light rays from striking the retina. Sometimes the effect can also be seen as bright flashes in the image.

FLUORESCEIN ANGIOGRAPHY:

A test to examine blood vessels in the eye. A dye is injected into a vein in the arm and pictures are taken as the dye passes through blood vessels in the eye.

FOCAL LENGTH: DETAIL

The distance for best focus of a lens or visual aid.

FOCAL POINT:

A point at which light rays converge or come together.

FOVEA:

The central part of the macula that provides the sharpest vision.

FUNDUS:

The interior lining of the eyeball, including the retina, optic disc, and macula; portion of the inner eye that can be seen during an eye examination by looking through the pupil.

GLAUCOMA: DETAIL

A condition of damage to the optic disc that surrounds the optic nerve, usually caused by increased pressure within the eye.

GONIOSCOPY:

An examination of the drainage area (Trabecular meshwork) to check for proper exit of aqueous fluid. This is done if high pressure is detected in the eye.

HYPEROPIA: DETAIL

Farsightedness; ability to see distant objects more clearly than close objects. May be corrected with glasses or contact lenses.

HORIZONTAL:

Across, as in side to side. Related: Vertical

INTRAOCULAR PRESSURE (IOP):

Fluid pressure inside of the eye. Minor variations are normal.

IRIS: DETAIL

The colored ring of tissue suspended behind the cornea and immediately in front of the lens; regulates the amount of light entering the eye by adjusting the size of the pupil.

KERATITUS: DETAIL

Inflammation of the cornea.

LACRIMAL GLAND: DETAIL

The small almond-shaped structure that produces tears. They are located just above the outer corner of the each eye.

LACRIMAL SAC: DETAIL

The area of collection for tear fluid to exit the eyes. They are located in the lower corner of the each eye nearest the bridge of the nose. Tear fluid leaves through the nasolacrimal duct.

LEGAL BLINDNESS: DETAIL

In the U.S., visual acuity of 20/200 or worse in the better eye with corrective lenses or visual field restricted to 20 degrees or less (tunnel vision) in the better eye. Related: VISION RATINGS.

LENS: DETAIL

The transparent, double convex (outward curve on both sides) structure suspended between the aqueous and vitreous; helps to focus light on the retina.

LID MYOKYMIA:

Twitching of the eyelid. May be due to tiredness or medical causes.

LOW VISION:

Visual loss that is enough to be classified as a vision limitation. Usually refers to vision that cannot be corrected with external visual aids.

LOW VISION SPECIALIST: DETAIL

A person who matches visual aids with people suffering from low vision.

MACULA: DETAIL

The small, sensitive area of the central retina; provides vision for fine work and reading.

MAGNIFICATION POWER: DETAIL

The degree of enlargement of objects with the use of visual aids.

MYOPIA: DETAIL

Nearsightedness; ability to see close objects more clearly than distant objects. May be correctable with glasses or contact lenses.

NORMAL:

This website refers to normal as the vision which each of us has individually when all is well with our particular vision. Related: Average

NYSTAGMUS: DETAIL

An involuntary rapid back and forth movement of the eyeballs.

OCCLUDER:

A device used to cover one eye during an examination.

OCULAR:

Relating to the eyes.

OPHTHALMODYNAMOMETRY:

The test which measures the blood pressure in the blood vessels within the retina.

OPHTHALMOLOGIST: DETAIL

An ophthalmologist is a Medical Doctor (MD) qualified to perform complete vision tests and diagnoses. They can treat vision problems either physically (visual aids), medically (drugs), or surgically.

OPHTHALMOSCOPE: DETAIL

A high powered magnification unit with a vertical beam of light which enables the doctor to see detail of the inner eye. Similar to the biomicroscope, but a handheld unit.

OPTIC CUP:

The white, cup-like area in the center of the optic disc.

OPTIC DISC/OPTIC NERVE HEAD:

The circular area (disc) where the optic nerve connects to the retina.

OPTIC NERVE: DETAIL

The bundle of over one million nerve fibers that carry visual messages from the retina to the brain.

OPTICAL INFINITY:

The minimum distance that an object needs to be from the eyes for the easiest focus.

OPTICIAM: DETAIL

An optician manufactures and/or dispenses eyeglasses, contact lenses or visual aids.

OPTOMETRIST: DETAIL

An optometrist is a Doctor of Optometry (DO) trained in all areas of optics and vision science.

PERIPHERAL VISION:

Area of the total visual field that is not within the range of direct vision (the object of attention being focussed on).

PHOTOPHOBIA:

A painful or extremely uncomfortable reaction to bright light.

POSTERIOR CHAMBER:

The area between the iris and the vitreous body.

PRESBYOPIA: DETAIL

The gradual loss of the eye's ability to change focus (accommodation) for seeing near objects caused by the lens becoming less elastic. Associated with aging; occurs to some degree in people over age 45.

PRESCRIPTION (visual aids):

The properties required for a visual aid to improve vision. This includes any magnification, convergence, or adjustments needed to compensate for a visual problem.

PUPIL: DETAIL

The adjustable opening at the center of the iris that allows varying amounts of light to enter the eye.

REFRACTION: DETAIL

The act of reflecting a light ray, usually in relation to reflecting a set of light rays onto a common focal point (the retina).

REFRACTION TEST:

A test to determine the optimal lenses to correct a refractive error in the eye.

REFRACTIVE ERROR: DETAIL

The measure of inability to focus images directly on the retina. Zero refractive error means proper focus.

RETINA: DETAIL DETAIL

The light-sensitive layer of tissue that lines the back of the eye which sends visual messages through the optic nerve to the brain. The retina is made up of ROD and CONE cells.

RETINAL DETACHMENT OR TEARING: DETAIL

When the retina either partly detaches from the back of the eye or develops a tear in the meshwork.

RETINAL PIGMENT EPITHELIUM (RPE):

The pigment cell layer that nourishes the retinal cells. Located just outside the retina and attached to the choroid.

RODS, ROD CELLS: DETAIL

One type of specialized light-sensitive cells (photoreceptors) in the retina that provide side vision and the ability to see objects in dim light (night vision). Related: CONES.

SCHLEMM'S CANAL:

The passageway for the aqueous fluid to leave the eye.

SCLERA: DETAIL

The tough, white, outer layer (coat) of the eyeball. It protects the sides and back of the eyeball.

TONOMETRY:

The standard to determine the fluid pressure inside the eye (intraocular pressure).

TRABECULAR MESHWORK:

The spongy, mesh-like tissue near the front of the eye that allows the aqueous fluid (humor) to flow to Schlemm's canal then out of the eye through ocular veins.

UVEA, UVEAL TRACT:

The middle coat of the eyeball, consisting of the choroid in the back of the eye and the ciliary body and iris in the front of the eye.

VERTICAL:

Up and/or down. Related: Horizontal

VISION RATINGS: DETAIL

Vision is rated according to what you can read on eye charts.

VISUAL ACUITY:

The level of ability to distinguish details and shapes of objects.

VISUAL AIDS: DETAIL

Any device that corrects or assists with vision. More commonly this means devices used by persons with very low vision.

VISUAL FIELD: DETAIL

The entire area that can be seen from the eye, including the direct vision and peripheral vision. It includes both the horizontal and vertical view a person can see. The area is measured in degrees.

VISUAL IMPAIRMENT: DETAIL

Visual impairment refers to a visual condition that blurs or blocks a section of vision.

VISUAL LIMITATION: DETAIL

Visual limitation refers to any condition that restricts the vision rather than blocks it.

VITREOUS: DETAIL

The transparent, colorless mass of gel that lies behind the lens and in front of the retina.

ZONULES:

The fibers which hold the lens in place and allow it to change to allow focus adjustments.