Eye Dictionary

Use this handy reference as a dictionary for all vision-related terms you may come across on this site:


ABLATE: in surgery, is to remove.

ABLATION ZONE: the area of tissue that is removed during laser surgery.

ACCOMMODATION: the ability of the eye to change its focus from distant objects to near objects.

ACUITY CLEARNESS: or sharpness of vision.

ASTIGMATISM: a distortion of the image on the retina caused by irregularities in the cornea or lens.


CATARACT: a clouding of the lens of the eye that affects vision. Most cataracts are related to aging. A cataract can occur in one or both eyes.

CONDUCTIVE KERATOPLASTY (CK): is a non-laser vision correction procedure that uses radio waves to help restore near vision for patients with presbyopia. CK was designed for farsighted individuals (hyperopes) over the age of 40 who would like an alternative to wearing reading glasses. CK is not intended for nearsighted (myopic) patients.

CORNEA: the clear, front part of the eye. The cornea is the first part of the eye that bends (or refracts) the light and provides most of the focusing power.

CORNEAL FLAP: a thin flap of the cornea which is lifted prior to LASIK.

CORNEAL HAZE: corneal clouding that causes the sensation of looking through smoke or fog.


DIOPTER: the measurement of refractive error. A negative diopter value signifies an eye with myopia and a positive diopter value signifies an eye with hyperopia.

DRY EYE SYNDROME: a common condition that occurs when the eyes do not produce enough tears to keep the eye moist and comfortable. Common symptoms of dry eye include pain, stinging, burning, scratchiness, and intermittent blurring of vision.


ENDOTHELIUM: the inner layer of cells on the inside surface of the cornea.

EPITHELIUM: the outermost layer of cells of the cornea and the eye’s first defense against infection.

EXCIMER LASER: an ultraviolet laser used in refractive surgery to remove corneal tissue.


GHOST IMAGE: a fainter second image of the object you are viewing.

GLARE SCATTER: from bright light that decreases vision.


HALOS: are rings around lights due to optical imperfections in or in front of the eye.

HYPEROPIA (OR FARSIGHTEDNESS): the inability to see near objects as clearly as distant objects and the need for accommodation to see distant objects clearly.


IN SITU: a Latin term meaning “in place” or “not removed”.

INFLAMMATION: the body’s reaction to trauma, infection, or a foreign substance, often associated with pain, heat, redness, swelling, and/or loss of function.

INFORMED CONSENT FORM: a document disclosing the risks, benefits, and alternatives to a procedure.

INTRAOCULAR CONTACT LENS IMPLANTATION (ICL): a form of outpatient surgery in which a surgeon adds an additional lens in front of the natural lens of the eye. The procedure is recommended for non-LASIK candidates between the ages of 30 and 45 whose natural lens is still capable of a wide range of accommodation.

IRIS: the colored ring of tissue suspended behind the cornea and immediately in front of the lens.


KERATECTOMY: the surgical removal of corneal tissue.

KERATITIS: inflammation of the cornea.

KERATO: prefix indicating relationship to the cornea.

KERATOCONUS: a disorder characterized by an irregular corneal surface resulting in blurred and distorted images.

KERATOMILEUSIS: carving of the cornea to reshape it.

KERATOTOMY: a surgical incision of the cornea.


LASER: the acronym for light amplification by stimulated emission of radiation. A laser is an instrument that produces a powerful beam of light that can vaporize tissue.

LASER EPITHELIAL KERATOMILEUSIS (LASEK): is a variation of both PRK and LASIK. Currently, the use of the excimer laser for LASEK is not FDA-approved. Additional studies will be necessary before LASEK is widely accepted as a viable procedure among corneal surgeons.

LASIK: the acronym for laser assisted in situ keratomileusis, which refers to creating a flap in the cornea with a microkeratome and using a laser to reshape the underlying cornea.

LENS: a part of the eye that provides some focusing power. The lens is able to change shapes, thereby allowing the eye to focus at different distances.


MICROKERATOME: a precision flap-making instrument that is affixed to the eye by use of a vacuum ring. When secured, a very sharp blade cuts a layer of the cornea at a predetermined depth.

MONOVISION: the purposeful adjustment of one eye for near vision and the other eye for distance vision.

MYOPIA (OR NEARSIGHTEDNESS): the inability to see distant objects as clearly as near objects.


OPHTHALMOLOGIST: a medical doctor specializing in the diagnosis and medical or surgical treatment of visual disorders and eye diseases.

OPTICIAN: an expert in the art and science of making and fitting glasses and may also dispense contact lenses.

OPTOMETRIST: a primary eye care provider who diagnoses, manages, and treats disorders of the visual system and eye diseases.

OVERCORRECTION: a complication of refractive surgery where the achieved amount of correction is more than desired.


PRESBYOPIA: the inability to maintain a clear image (focus) as objects are moved closer. Presbyopia is due to reduced elasticity of the lens with increasing age.

PRK: the acronym for photorefractive keratectomy, which is a procedure involving the removal of the surface layer of the cornea (epithelium) by gentle scraping and use of a computer-controlled excimer laser to reshape the stroma.

PUPIL: a hole in the center of the iris that changes size in response to changes in lighting. It gets larger in dim lighting conditions and gets smaller in brighter lighting conditions.


RADIAL KERATOTOMY: commonly referred to as RK; a surgical procedure designed to correct myopia (nearsightedness) by flattening the cornea using radial cuts.

REFRACTION: a test to determine the refractive power of the eye; also, the bending of light as it passes from one medium into another.

REFRACTIVE ERRORS: hyperopia, myopia, and astigmatism.

REFRACTIVE LENS EXCHANGE (RLE): a form of outpatient surgery in which a surgeon replaces the natural lens of the eye with an artificial lens with a power calculated based on the pre-operative determination of the power of your eye. RLE is for individuals aged between 45 and 75 years old.

REFRACTIVE POWER: the ability of an object, such as the eye, to bend light as light passes through it.

RETINA: a layer of fine sensory tissue that lines the inside wall of the eye. The retina acts like the film in a camera to capture images. It then transforms the images into electrical signals, and sends the signals to the brain.


SCLERA: the tough, white, outer layer (coat) of the eyeball that, along with the cornea, protects the eyeball.

SNELLEN VISUAL ACUITY CHART: one of many charts used to measure vision.

STROMA: the middle, thickest layer of tissue in the cornea.


UNDERCORRECTION: a complication of refractive surgery where the achieved amount of correction is less than desired.


VISUAL ACUITY: the clearness of vision; the ability to distinguish details and shapes.

VITREOUS HUMOR: the transparent, colorless mass of gel that lies behind the lens and in front of the retina that fills the center of the eyeball.

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