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Eye Care Glossary


The ability of the eye to change focus from distance to near. This ability is gradually lost after age.

Accommodative Insufficiency:
Loss of, or less than the age appropriate amount of accommodation.

The accessory structures of the eye, including the Eyelids, Lacrimal Gland, Lacrimal Ducts, etc.

Automated Lamellar Keratoplasty (removal of a part of the central Corneal Stroma) to effect a change on the refractive error.

Partial of total blindness.

Refractive condition in which parallel rays do not focus on the Retina; manifestation if refractive error.

Often called "lazy eye". It is a condition in which the best corrected vision in one eye is poorer than 20/20 (6/6) in the absence of any obvious structural anomalies or ocular disease.

Amsler Grid:
A hand held chart featuring equally spaced horizontal park and vertical lines, usually white on black background, used to detect central visual field defects.

A condition of unequal refractive state for the two eyes.

Anterior chamber:
The front section of the eye’s interior where aqueous humor flows in and out of providing nourishment to the eye and surrounding tissues.

Anterior segment:
The part of the eye anterior to the crystalline lens including the Cornea, Anterior Chamber, Iris and Ciliary Body.

Micro-nutrients which destroy or neutralize free radicals. Molecules which have been implicated as one causative factor in the stimulation of abnormal cellular reproduction (cancer) and cellular destruction (aging).

The absence of the eye’s natural crystalline lens, usually after Cataract removal.

Aphakic Spectacles:
Thick, plus-powered eyeglasses that were once the standard optical correction following extraction of Cataract. The glasses were cumbersome and greatly distorted peripheral vision. Today, an Intraocular Lens (IOL) is implanted in the eye after the Cataract is removed to replace the focusing power of the natural lens eliminating the need for Aphakic Spectacles.

ARMD: Age Related Macular Degeneration:
Degeneration of the photoreceptors in the Macular (central) region of the Retina resulting in decreased central vision.

Subjective symptoms or distress arising from the use of the eyes; as in eyestrain.

A refractive error caused by unequal refraction of light in different meridians, resulting in a distorted and blurred image.

Astigmatic Keratotomy (AK):
An incisional refractive surgical technique in which transverse incisions are made in the cornea to reduce or eliminate astigmatism.

Binocular Vision:
The simultaneous use of the two eyes. Normal binocular vision yields a stereoscopic image and depth perception.

An opacity or loss of transparency of the crystalline lens which results in loss of light transmission, image degradation and reduced vision.

The thin, blood-rich membrane that covers the white of the eyeball; responsible for supplying blood to the Retina.

Ciliary Body:
The part of the eye that produces Aqueous Humor.

Inflammation of the Conjunctiva maybe caused by bacteria, virus, allergens or chemicals.

The thin transparent membrane overlying the Sclera (white part of the eye) and inside surface of the eyelid.

The turning of the eyes simultaneously inwards/outwards so that they are both "aimed" towards the object being viewed

The clear front surface of the eye. The transparent "window" and primary refractive surface of the eye.

Corneal Curvature:
The shape of the front surface of the eye.

Crystalline Lens:
The natural lens of the eye, located behind the pupil, which helps bring rays of light to focus on the Retina, The original state of the lens is transparent, but the lens becomes cloudy with age (see Cataract).

Depth Perception:
The ability of the vision system to perceive the relative positions of objects in the visual field.

A unit measurement of the degree to which light converges or diverges. Diopters are used to define a lens’s refractive power. Equal to the reciprocal of the focal length of a lens (in meters), e.g., a 2-diopter lens brings parallel rays of light to a focus at half a meter.

A condition in which a single object is perceived as two; also called "double vision".

Refractive condition in which no refractive error is present and distant images are focused sharply on the Retina with no need for corrective lenses.

The position of the eyes in an over-converged position compensated by the external eye muscles so that the eyes do not appear turned inward.

The position of the eyes in an over-converged position so the non-fixating eye is turned inward.

The position of the eyes in an over-diverged position compensated by the external eye muscles so that the eyes do not appear turned outward.

The position of the eyes in an over-diverged position so that non-fixating eye is turned outward.

Extra-Ocular/External Ocular Muscles:
The six muscles that turn the eyes to position them appropriately for viewing objects in various fields of view.

Extracapsular Cataract Extraction (ECCE):
A surgical procedure which removes the Cataractous lens but leaves the rear lens capsule in place.

Functional Visual Disability:
The degree to which a visual error interferes with a person’s ability to perform normal daily activities, such as, reading, driving at night, or enjoying hobbies.

Characteristic optic nerve damage often associated with abnormally increased intraocular pressure and loss of visual field.

Loss of one half of the visual field in one or both eyes.

(Far-sightedness, long-sightedness): A refractive condition which light entering the eye is focused virtually behind the Retina, resulting in a blurred image.

A deficiency of oxygen supply to a tissue

Intraocular Lens (IOL):
A plastic lens that is surgically implanted to replace the focusing power of the natural lens of the eye following Cataract extraction. There are numerous styles of IOLs, including foldable IOLs and multifocal IOLs.

Intraocular Pressure:
The internal fluid pressure within the eye created by the continual production and drainage of aqueous fluid in the anterior chamber.

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

Inflammation of the Cornea.

Laser Assisted In Situ Keratomileusis (LASIK):
Laser Assisted In Situ Keratomileusis, or LASIK, combines Excimer Laser PRK with elements of ALK used to reduce refractive error.

Lens: (also called crystalline lens):
The transparent structure inside the eye that focuses light rays onto the Retina.

The portion of the eye that allows us to see fine details clearly.

Macular Degeneration:
Degeneration in the Macular region of the Retina that results in decreased central vision and sometimes in blindness.

Macular Edema:
A collection of fluid in and under the Macular portion of the Retina.

Pupillary constriction.

Pupillary dilation.

(Nearsightedness, short-sightedness) (UK): A refractive condition in which light entering the eye is focused short of the Retina, resulting in blurred image.

Near Point Of Accommodation:
The closest point in front of the eyes that an object may be clearly focused.

Near Point Of Convergence:
The maximum extent the two eyes can be turned inward.

The formation of new blood vessels, often fragile and inappropriate for the location.

A rapid, repetitive, involuntary movement or rotation of the eyes.

Ocular Hypertension:
High ( greater than 21 mm Hg) intraocular pressure.

A physician specializing in medical and surgical treatment of eye diseases and disorders.

Optic Nerve:
A bundle of more than 1 million nerve fibers that connects the retina with the brain. The optic nerve is responsible for interpreting the impulses it receives into images.

Optic Neuritis:
A condition of inflammation of the optic nerve.

A non-surgical procedure using contact lenses to alter the shape of the Cornea to effect a change in the refractive error.

Non-inflammatory swelling/elevation of the optic nerve due to increased intracranial pressure.

Phacoemulsification (fay-koh-ee-mul-sih-fih-KAY-shun):
A form of extracapsular cataract extraction in which an ultrasonic instrument is used to shatter and break up a Cataract, making it easier to remove.

Sensitivity to light.

Photorefractive Keratotomy (PRK):
A technique employing an Excimer Laser to reshape the surface of the Cornea and thereby reducing nearsightedness.

A (usually) irritation caused by degeneration of the Conjunctiva resulting in a thickening and yellowing of the normally thin transparent tissue.

Posterior Capsular Opacification (PCO):
Opacification of the posterior lens capsule following Cataract extraction. Sometimes called "After Cataract," and may cause blurred vision.

Posterior Chamber:
The back section of the eye’s interior.

Posterior Segment:
The part of the eye posterior (behind) to the crystalline lens, including the Vitreous, Choroid, Retina and optic nerve.

Posterior Vitreous Detachment (PVD):
The separation of the vitreous body from its attachment to the Retinal surface due to shrinkage from age, degenerative or inflammatory conditions or trauma.

Loss of accommodative ability as the eye fails to allow for the focusing of near objects, resulting from age-related changes in the crystalline lens or Ciliary muscle.

An optical element which deviates the path of light.

Drooping of the upper or lower eyelid from its normal position.

The center hole in the Iris through which light must pass to reach the back of the eye.

Pupillary Response:
The constriction and dilation of the pupil due to stimulation by light of accommodation.

Radial Keratotomy (RK):
A surgical procedure using diamond scalpel blades to create linear incisions into the Cornea which result in the flattening of the tissue and thereby altering the refractive error.

A determination of the optical error of the eye.

Refractive Error:
The degree to which images received by the eyes are not focused on the Retina, e.g.: Myopia, Hyperopia, Astigmatism.

The thin neurological tissue which line the back wall of the eye which receives light and converts it to electrical signals for transmission via the optic nerve to the brain.

Retinal Detachment:
A separation of the retina from the back wall of the eye. Results in loss of vision in the detached area. Repairable with fair to good prognosis for vision in the early stages.

The white visible portion of the eyeball. The muscles that move the eyeball are attached to the Sclera.

An area of partial or complete loss of vision surrounded by an area of normal vision.

The condition in which binocular fixation is not present; commonly referred to as "cross eyed".

The ability to perceive three dimensional depth.

The inability to perceive all or part of objects in the field of vision of one eye.

Suspensory Ligament of Lens:
A series of fibers that connect the Ciliary body of the eye with the lens, holding it in place.

A procedure for the measurement of intraocular pressure.

Ultraviolet Radiation:
Radiant energy with a wavelength just below that of the visible light. UV-c is the shortest wavelength at 200-280nm and is absorbed by the atmosphere before reaching the surface. Extremely damaging to living tissue. UV-b, at 280-315nm is "burning rays" of the sun and is damaging to most living tissue. UV-a, at 315-400nm are "tanning rays" of the sun and is somewhat damaging to certain tissues, UV radiation has been described as a contributing factor to the processes which result in ARMD and Cataracts.

Vision Therapy:
(Orthopedics, vision training, eye exercises) a treatment process for the improvement of visual perception and / or coordination of the two eyes for efficient and comfortable binocular vision.

Visual Acuity:
A measure of spatial resolution. The measure of the ability to visually discriminate.

Visual Field:
The area or extent of space visible to an eye in a given position of gaze.

Vitreous Body:
A clear, jelly-like substance that fills the center of the eye.

The gel-like transparent fluid substance filling the posterior four fifths of the globe between the crystalline lens and Retina.


YAG Laser:
The YAG Laser is an instrument that emits a short pulsed, high energy light beam that can be precisely focused to cut, vaporize, or fragment tissue.


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