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Terminology - Common Definitions in Eye Care

Learn more about common terms regarding the eye. Your ophthalmologist will be amazed!
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Amblyopia | Anterior Chamber | Aqueous Humor | Astigmatism | Blepharitis | Cataract | Choroid | Ciliary Body | Conjunctiva | Cornea | Dry Eye | Farsightedness | Flashes of Light | Floaters | Glaucoma | Hyperopia | Iris | Lacrimal Gland | Lacrimal sac | Lens | Macular Degeneration | Myopia | Nearsightedness | Occipital Lobe | Optic Nerve | Photopsia | Presbyopia | Pupil | Refraction | Refractive Error | Retina | Retinal Detachment | Sclera | Strabismus | Uveitis | Vitreous |


Amblyopia

Term meaning "lazy eye". This develops when the brain chooses to "ignore" the "bad" eye resulting in poor vision in that eye even though the eye itself is normal. This can result from numerous causes, the most common of which is strabismus (crossed eyes). See strabismus this section, or click for more details.

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Anterior Chamber

A fluid-filled space between the cornea and pupil. The fluid is called aqueous humor, and contains the necessary elements that nourish and protect the cornea and other structures. This is a highly important anatomic area of the eye and is the focus for many diseases that can occur such as glaucoma, cataract, uveitis, just to mention a few.

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Aqueous Humor

anterior chamber (please see this section) between the cornea and pupil.

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Astigmatism

An optical error in which there are two or more abnormal focal point in the eye, unlike hyperopia (farsightedness) or myopia (nearsightedness) where there is just one abnormal focal point that needs correcting. (See Refractive Disorders for more details.) With astigmatism, both near and distance vision are blurred. This is a common condition and is frequently present in a glasses prescription.

 

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Blepharitis

Infection or inflammation of the rim of the eyelid. Often referred to as "granulated eyelids." This is frequently due to infection of the oil glands around the lid margin, but can also be associated with dandruff, some forms of acne, and eye makeup.

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Cataract

A clouding condition of the natural lens inside the eye. This causes a fog or "skim" over the vision, and can cause washed out colors, halos around lights, glare, and light sensitivity. (Click for more information on cataracts.)

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Choroid

Part of the middle coat of the eye which is a major source of blood supply. It is sandwiched in between the retina and sclera (see definitions this section).

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Ciliary Body

A large muscle in the eye that enables the eye to focus at different distances. It also produces the fluid (aqueous humor) that circulates and nourishes the internal eye.

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Conjunctiva

A flimsy transparent membrane covering the outer part of the eye and the inner layer of the eyelids. In addition to protecting the eye, it secrets mucous to lubricate the eye and reduce friction between the eyelids and eyeball.

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Cornea

A clear membrane that lies in front of the iris (colored part of the eye) and pupil. It is commonly referred to as the "front of the eye." It is literally the window to the eye and has tremedous focusing power for the eye. It determines 80% of the refractive power of the eye. It also greatly magnifies the internal eye structures that allows an examiner to view the inside of the eye in great detail. It is rich in sensory nerves which explains the extreme sensitivity of the eye to scratches and foreign bodies. (See Eye Anatomy and How The Eye Works for more details.)

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Dry Eye

A condition that occurs when the tear gland (See lacrimal gland this section) produces less tears creating a dry eye surface. (For more information, please see

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Farsightedness

(Hyeropia) An optical error in which the eye sees better at a distance than near without correction. (See Refractive Disorders for more details.) Individuals may not recognize any sense of blurred vision at near depending upon their age and degree of hyperopia. Mild degrees of hyperopia may in fact go un-noticed until the 30’s or 40’s.

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Flashes of Light

See Photopsia.

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Floaters

The perception of little dots, strands, "spidery-like" images that are noticeable under certain lighting conditions. As we age, the normally transparent vitreous gel liquifies and forms little particles and fibrous strands. This debris accumulates in the gel and becomes suspended. When light enters the eye, those strands and debris cast shadows onto the retina. They are usually harmless. However, showers of spots or abrupt increase in the numbers of spots can be a sign of a retinal tear, particularly if associated with photopsia (please see this section). This demands immediate evaluation by an ophthalmologist.

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Glaucoma

A disease process that causes deterioration to the optic nerve fibers resulting in visual loss. The causes of glaucoma are numerous, most commonly due to elevated fluid pressure inside the eye. Damage that occurs due to sudden rise of pressure is known as "acute" glaucoma. More often, however, damage to the optic nerve occurs when fluid pressure is higher than normal over a long period of time. This is called chronic glaucoma and is generally silent and painless. (See FAQ’s on glaucoma for more details.)

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Hyperopia

(farsightedness): An optical error in which the eye sees better at a distance than near without correction. (See Refractive Disorders for more details.) Individuals may not recognize any sense of blurred vision at near depending upon their age and degree of hyperopia. Mild degrees of hyperopia may in fact go un-noticed until the 30’s or 40’s.

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Iris

Generally known as the "colored" part of the eye. It protects the eye from too much light, and it contains the sphincter and dilating muscles that allow the pupil size to vary.

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Lacrimal Gland

A small gland that secrets tears to bathe, nourish, and protect the front part of the eye. This gland is located behind the bone at the tail end of your eyebrow called the superior orbital rim. Disorders of this gland can cause a dry eye problem and is common with advancing age. It is frequently involved in diseases such as rheumatoid arthritis and other problems.

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Lacrimal sac

A little structure that drains away tears. Little channels called canaliculi are present in the inner corner of the eyelids into which tears drain. From there, they are dumped into the lacrimal sac and then drained into the nose and throat. Disorders of this structure leads to a back flow of tears and mucous and is a common cause of watery, teary eyes.

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Lens

The structure that sits behind the pupil and which acts to focus light onto the retina just as a camera lens focus light onto the film inside. (See Eye Anatomy and How The Eye Works for more details.) The lens is normally crystal clear, and cannot be seen with the naked eye. When it becomes cloudy, it is called a cataract.

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Macular Degeneration

Deterioration of the macular region of the retina resulting in loss of central vision. (See FAQ’s on Macular Degeneration for an extensive discussion.)

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Myopia

(near sightedness): An optical error in which the eye sees better at near than at distance without proper correction. (See Refractive Disorders for more details.)

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Nearsightedness

(Myopia) An optical error in which the eye sees better at near than at distance without proper correction.

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Occipital Lobe

The final part of the visual pathway for vision. It is the part of the brain that does the "seeing." It receive electrical impulses from the retina via the optic nerve. Strokes that involve the occipital lobe can cause blindness even though the eye and its structures are functioning normally.

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Optic Nerve

The nerve endings that are contained in the retina that come together to form one large optic nerve. This nerve exits the back of the eye and connects the eye with the part of the brain that is responsible for vision. (See Eye Anatomy and How The Eye Works for more details.)

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Photopsia

A term meaning light flashes or the sensation of flickering of lights. It is a visual phenomena that is usually benign, but could be an early indication of a retinal tear or detachment. It is caused by shrinkage that occurs with the vitreous gel in the back of the eye. Because the vitreous is attached to retina, changes in the vitreous body (shrinkage, liquefaction, separation, etc.) pulls on the retina causing it to discharge electrical impulses. These impulses are then picked up by the brain as "flashes" and "flickers." Such changes in the vitreous are often due to aging of the eye. Increasing photopsia or photopsia as an initial occurrence should be immediately evaluated by an ophthalmologist, especially if they occur with floaters (See Floaters this section).

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Presbyopia

A universal aging process that occurs in all people regardless of whether or not glasses were necessary as a child or during young adulthood. This is a loss of the ability to focus on near objects. It generally becomes evident during the 40's and will generally worsen until the age of 65 or 70, at which time it plateaus. During this time, progressively stronger reading glasses or bifocals become necessary. The severity of symptoms and age of onset may be influenced by the degree of myopia (nearisightedness) or hyperopia (farsightedness) and individual may have. (See Refractive Disorders for more details.)

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Pupil

The opening created by the iris through which light passes on to the retina. Unlike what is generally believed, this structure only regulates the amount of light entering the eye and does not actually "focus," although depth of field is affected by the size of the pupil in the same way that depth of field is affected by the aperature stop in a camera.

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Refraction

Part of an eye exam that determines the optical error of the eye. This is often used to measure for the strength of glasses or contacts needed to see well. It is useful in determining if there were any changes in the eye\'s ability to focus as seen in developing cataracts or poorly controlled diabetes.

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Refractive Error

The optical error of the eye, commonly known as nearsightedness, farsightedness, or astigmatism.

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Retina

The inner lining of the eye containing millions of nerve cells, and is often compared to the film inside of a camera. The retina actually does not "see" but is an electrically sensitive membrane which pick up light rays entering the eye, processes and "packages" them, and transmits them to the brain as electrical impulses where they are decoded into what we know as vision. (See Eye Anatomy and How The Eye Works for more details.)

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Retinal Detachment

When the retina becomes elevated off the wall of the eye, similar to a blister that forms on the skin or wallpaper coming off the wall. When this happens, the retina becomes separated from its blood supply, and that portion of the retina ceases to function. This is a potentially blinding condition that requires major surgery to repair it. (Click retinal detachment for more details.)

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Sclera

The outer wall of the eye. Some know it as the "white" part of the eye.

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Strabismus

Term meaning "crossed eyes." This happens when the muscles around the eye are not in proper alignment resulting in one eye crossing in, out, up, or down. This can lead to amblyopia (reduced vision or "lazy eye") in the eye that is crossed. See amblyopia this section, or click strabismus for more details.

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Uveitis

An inflammatory process inside the eye involving the middle coat of the eye called the uvea. The middle coat is sandwiched in between the sclera (outer coat) and the retina, and it is a major source of blood supply and nutrition for the eye. The parts of the middle coat are the iris, ciliary body, and the choroid. There are many causes for uveitis. Sometimes, it is called iritis.

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Vitreous

The gel-like substance that fills the inside of the eye between the lens and the retina.

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