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Eye Health Glossary

Do you suffer from ambloyopia, aniridia or astigmatism? Can you point out the differing functions of the cornea, iris, and pupil? Browse an extensive list of eye-related words, phrases, and definitions in our glossary of common eye health terminology.

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Accommodation: the ability of the eye to change its focus from a close object to a far object, and vice versa. This ability declines with age; typically by the age of 50, so much near focusing power has been lost that reading glasses are necessary. See ‘presbyopia.’

Accommodative spasm: a condition that causes the eye muscle to focus, or accommodate, constantly and automatically.

Ambloyopia: an eye disorder of coordination between the eye and the brain; commonly called lazy eye.

Aniridia: a rare genetic eye condition characterized by a lack of a full or partial iris, causing severe light sensitivity.

Arcus: a yellow or white band around the circumference of the peripheral cornea, which signifies fatty or oily deposits in the cornea. This is a common and benign condition, typically seen in seniors. When seen in a person less than 40 years of age, the condition may signify high cholesterol.

Astigmatism: a fairly common condition in which the corneal or lens surface is unevenly shaped, causing one to see shadowing of images.

Automated lamellar keratoplasty (ALK): an older form of refractive surgery used to correct nearsightedness, which involves creating a thin corneal flap with a Microkeratome, a precision surgical instrument with an oscillating blade, and slicing a second, deeper cut to eliminate a lamellar slice of cornea.

Best corrected visual acuity (BCVA): the best possible vision one can attain via corrective lenses.

Blepharitis: a chronic inflammatory condition of the eyelids, common in children and adults. The condition causes symptoms including redness, burning, itching, swollen and crusty lids and dry-eye.

Blind spot: a small area of the retina in which the optic nerve enters the eye and no vision exists, thus creating a small gap in the visual field. This is normal and present in all people.

Cataract: a clouding that develops in the eye’s crystalline lens or in its envelope, varying in degree from slight to total opacity and obstructing the passage of light.

Cornea: the eye’s clear front wall, which works with the crystalline lens to focus light on the retina. The cornea is approximately the thickness of a standard credit card, and may be reshaped to help correct vision with laser refractive surgery.

Crystalline lens: a structure inside of the human eye which functions to focus light onto the retina, similar to the lens of a camera. This lens is able to modify its focusing power to let the eye focus on objects that are both close and far in distance (see ‘accommodation’).

Dilate: to stretch or expand. ‘Dilate’ originates from the Latin verb “dilatare.” Drops are put in the eye to dilate the pupil, so that an eye exam may be performed. A dilated pupil allows for easier view of the crystalline lens.

Dermatochalsis: a condition during which the upper eyelid skin looses elasticity and sags, giving the upper eyelids a heavy look. The sagging skin may become so extreme that it limits the superior visual field. This condition can be corrected by a blepharoplasty, or a surgical removal of the excess eyelid skin. The condition is age-related.

Glaucoma: a condition of the eye in which the optic nerve is damaged, first resulting in loss of peripheral vision. As time passes, central vision can also be lost and complete blindness can follow. The condition is typically related to high eye pressure and current treatment is targeted at decreasing eye pressure with drugs or surgery. See ‘intraocular pressure.’

Hyperopia: a condition in which light entering the eye is not properly focused on the retina, but rather on some point behind the retina. The resulting vision is clear in regard to distant objects, but blurry when close objects are viewed; commonly called farsightedness.

Intraocular pressure (IOP): pressure within the eye resulting from the constant creation of eye fluid, the aqueaous humor. IOP is monitored closely in glaucoma patients and in those suspected of having glaucoma. Decreasing one’s IOP is the basis of glaucoma treatment.

Iris: a colored structure in the front section of the eye which functions as a diaphragm to direct the amount of light entering the eye.

Laser correction: surgical techniques that use an excimer laser to correct sight-related ailments by reshaping the cornea . LASIK surgery has no effect on the eye’s focusing muscles, so it does not correct typical presbyopia cases. Also called ‘laser-assisted in situ keratomileusis’ or ‘LASIK.’

Lens: the transparent structure found within the eye that functions to focus light rays onto the retina.

Monovision: is the term bestowed on the science of appropriating contact lenses for a patient who suffers from presbyopia. With monovision, the dominant eye is focused for distance vision, and the non-dominant eye is focused for near to intermediate.

Myopia: a condition in which light entering the eye is not properly focused on the retina, but rather on some point in front of the retina. The resulting vision is clear for objects close to the eye, but blurry for distant objects. Commonly called nearsightedness.

Nonprescription eyeglasses or lenses: eyeglasses or lenses typically intended for people who have trouble reading small print; prescriptions may be written for these items but are not necessary for their purchase.

Ophthalmologist: a medical doctor, M.D., who may perform refractions on, surgeries on, and prescribe medications for eyes.

Optic nerve: a structure at the back of the eye that gathers the retina’s neuron signals and transmits them to the brain. This nerve can become damaged as a result of diseases such as glaucoma, causing loss of vision.

Phacoemulsification: the procedure of surgically eradicating a cataract, using ultrasound to help split the clouded crystalline lens into small bits.

Presbyopia: a condition of the eye in which it can no longer change focus to view near objects. As humans age, the lens within the eye loses flexibility, thus causing difficultly in close-up focusing because the eye is no longer able to change its shape and effectively bend light rays as sharply. This condition typically develops around between ages of 35 and 40 and progresses until approximately between the ages of 55 and 65. Presbyopia is diagnosed via a comprehensive eye examination.

Prescription: a physician’s order for the preparation and administration of a drug or device. A prescription includes the superscription or heading with the symbol “R” or “Rx”, which stands for the word recipe; the inscription, which contains the names and quantities of the drug or device’s necessary components; the subscription or directions for producing the drug; and the signature.

Pupil: The opening of the iris, which may appear to dilate (open) or constrict (close). The pupil determines the amount of light let into the eye.

Refraction: the process of determining a person’s glasses prescription, during which an instrument called a phoroptor situates varying power lenses in front of the eye. The combination of lenses that provides the sharpest vision determines a patient’s refraction.

Refractive Error: an eye irregularity in which incoming light is not focused clearly on the retina, causing blurry vision. Refractive error is categorized as myopia, or nearsightedness; hyperopia, or farsightedness; and astigmatism.

Retina: the layer of light-sensitive nerve lining the back portion of the eye. The retina receives images formed by the lens and transmits these images to the brain via the optic nerve.

Short-armed-syndrome: see ‘presbyopia.’

Slit lamp examination: an eye examination that utilizes a particular microscope, called a slit lamp, which allows for thorough inspection of the front portion of the eye.

Uveitis: an inflammation of the iris and pigmented tissues within the eye due to infection or an irregular immune reaction.

Visual acuity: a gauge of the sharpness of vision typically calculated in the United States by the Snellen, or “20/20” classification. In this system, “20/20” represents normal vision. As vision worsens, the bottom number increases, necessitating the person to be nearer to an object to see it well.

Resources for Eye Health Terms


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