Glossary
Glossary
ablate
To surgically remove; to vaporize. In LASIK, an excimer laser is used to ablate a small amount of corneal tissue to reshape the eye and thereby correct vision.
ablation zone
The circular area in the center of the cornea that the excimer laser treats to correct vision.
The total LASIK ablation zone is usually 7 to 9 millimeters in diameter and includes a central optical zone (OZ) and a small transition zone between the OZ and the untreated peripheral cornea.
accommodation
The ability of the eye to increase its refracting power to focus on near objects. In a normal eye, accommodation is needed only to see near objects clearly. No accommodation is required to see distant objects. As we age, our eyes' ability to accommodate diminishes. This normal age-related loss of accommodation is called presbyopia. Because of presbyopia, most LASIK patients over age 40 need reading glasses to see near objects clearly.
acuity
Clarity or sharpness of vision. Visual acuity is typically measured using letter charts and is quantified by means of the Snellen fraction (i.e. 20/20, 20/40, etc.)
all-laser LASIK
LASIK wherein the surgeon uses an IntraLase femtosecond laser (laser microkeratome) to create the corneal flap, rather than using a mechanical (bladed) microkeratome. Also called "blade-free LASIK" and (infrequently) "IntraLASIK".
amblyopia
Poor vision that cannot be corrected with glasses or contact lenses in an otherwise healthy eye. Amblyopia, commonly called "lazy eye," affects up to 5 percent of the population and can be caused by improper eye alignment (strabismus) and/or unequal amounts of farsightedness or nearsightedness in the two eyes.
astigmatism
Unequal curvature of the eye that causes blurred vision at all distances.
Astigmatism causes certain aspects of objects to appear more blurred than others, and may produce "ghosting" or double images. LASIK can correct astigmatism.
autoimmune disease
Any of a varied group of serious, chronic illnesses that can affect almost any part of the body. Autoimmune diseases are characterized by a misdirected immune response in which the body's immune system (which normally protects the body from disease and infection) attacks the very tissues it normally protects. Examples of autoimmune disease include: Type 1 diabetes, rheumatoid arthritis, lupus, multiple sclerosis (MS), Crohn's disease, and Graves' disease.
best corrected visual acuity (BCVA)
The best eyesight a person can achieve with corrective eyeglasses or contact lenses.
best spectacle-corrected visual acuity (BSCVA)
The best eyesight a person can achieve with corrective eyeglass lenses.
blepharitis
Inflammation of the eyelids, characterized by redness, itchiness, and the accumulation of flaky debris (similar to dandruff) at the base of the eyelashes. Blepharitis is usually caused by staphylococcus bacteria, which may also lead to the formation of a stye. The standard treatment for blepharitis is lid scrubs and topical antibiotic medicine (eye drops or ointments).
cornea
The clear front part of the eye. The cornea provides about 70% of the focusing power of the eye. LASIK alters corneal curvature to enable the eye to focus light more accurately. The human cornea is about 500 microns (one-half of a millimeter) thick.
cylinder power
The type of eyeglass or contact lens power required to correct astigmatism.
diopter (D)
The unit of measurement used to quantify refractive error and lens power.
Prescription lenses to correct nearsightedness have a negative (-) diopter value. Lenses to correct farsightedness and presbyopia have a positive (+) diopter value.
dominant eye
The eye that points directly at the object you are viewing. Believe it or not, our eyes don't ever point exactly in the same direction. The eye that points directly at an object is called the dominant eye. The other (non-dominant) eye points slightly to the side of the object. This normal difference in eye direction helps our visual world appear 3-dimensional.
To determine which eye is your dominant eye, perform this simple exercise:
- Look at a small object in the distance.
- Extend one arm. (If you are right-handed, extend your right arm.)
- Put your thumb up and position your thumb directly in front of the object. (Keep both eyes open and don't move your arm or thumb!)
- Close one eye. If your thumb is still in front of the object, your open eye is your aligned dominant eye. If your thumb has moved significantly off to the side, your open eye is not aligning your thumb with the object. This is your non-dominant eye.
Determining which eye is your dominant eye is important if you're considering monovision LASIK. For comfortable monovision, it's important that your dominant eye is the eye corrected for clear distance vision and your non-dominant eye is the eye made slightly nearsighted for seeing objects up close.
dry eye syndrome (DES)
A common condition that occurs when the lacrimal glands don't produce enough tears to keep the eyes moist and comfortable. Symptoms of dry eye include burning, stinging, scratchiness, a feeling something is "in" the eye, and intermittent blurred vision. LASIK temporarily decreases tear production and may cause dry eye symptoms that can last for several weeks. Dry eye symptoms from LASIK are usually managed successfully with the frequent use of artificial tears.
ectasia
Bulging of the cornea due to a weakening of the tissue. A very infrequent but serious complication of LASIK surgery.
edema
Swelling due to excess fluid. Corneal edema may be present for several weeks after LASIK surgery.
endothelium
The single layer of cells lining the back surface of the cornea. The endothelium acts like a pump to maintain the proper amount of fluid inside the cornea. Failure of the endothelium leads to corneal swelling and blurred vision.
epithelial ingrowth
A complication of LASIK characterized by the growth of cells from the superficial layer of the cornea (the epithelium) under the corneal flap. If not removed, epithelial ingrowth can cause discomfort, blurred vision, and flap complications.
epithelium
The outer layer of fast-growing cells on the cornea. The epithelium blocks dust, water, bacteria and other foreign materials from entering the cornea. It also provides a smooth surface for the tear film and absorbs oxygen and nutrients from the tears and distributes these nutrients to the rest of the cornea. The epithelium comprises about 10% of the total corneal thickness.
excimer laser
A medical laser used in LASIK and other vision correction surgery. Excimer lasers use very short pulses of ultraviolet (UV) rays to ablate (vaporize) tissue to reshape the cornea, enabling the eye to better focus light. The duration of each pulse of an excimer laser is measured in nanoseconds. A nanosecond is one-billionth of a second. (See also: femtosecond laser.)
farsightedness
The common term for hyperopia.
FDA
The abbreviation for the U.S. Food and Drug Administration. In the United States, the FDA is the government agency that evaluates and approves medical devices, including laser systems for LASIK and other types of refractive surgery.
femtosecond laser
A medical laser used in LASIK and other vision correction surgery. Femtosecond lasers use ultra-short pulses of low-energy infrared rays to cleave tissue bonds (creating microscopic bubbles) at a precise depth below the surface of the cornea. The duration of each pulse is measured in femtoseconds. A single femtosecond is one-billionth of a millionth of a second. Femtosecond lasers are used to create the corneal flap in LASIK surgery prior to the reshaping of the eye performed with an excimer laser.
ghost image
A faint, second image surrounding the primary image of an object. Uncorrected astigmatism after LASIK can be a source of ghost images and blurred vision.
glare
Scatter from bright light that decreases vision. Corneal edema can be a source of glare and decreased vision for several weeks after LASIK.
halos
Luminous rings appearing around lights. Corneal edema or optical imperfections in the eye after LASIK may cause halos, either temporarily or permanently.
haze
Diffuse clouding of the cornea that causes the sensation of looking through smoke or fog.
higher order aberrations (HOA)
Optical imperfections of the eye other than nearsightedness, farsightedness, astigmatism or presbyopia. HOA cannot be corrected with eyeglasses or contact lenses. Standard LASIK may increase HOA. Customized, wavefront-assisted LASIK can reduce higher order aberrations and therefore may provide better vision than eyeglasses, contact lenses or standard LASIK.
hyperopia
The inability to see near objects as clearly as distant objects and/or the need to use extra focusing effort to see distant objects clearly. Also called farsightedness.
inflammation
The body's normal reaction to trauma, infection or a foreign substance, characterized by pain, heat, redness, swelling and/or loss of function. Some inflammation of the cornea is normal after LASIK. You will be given an anti-inflammatory eye drop medication to use for a week or so after LASIK surgery to control post-operative inflammation.
Informed Consent form
A document disclosing the risks, benefits and alternatives to a surgical procedure. You will be given an Informed Consent form to review and sign prior to LASIK surgery.
intraocular
Inside the eye. LASIK alternatives phakic IOL implantation and clear lens extraction are intraocular refractive surgery procedures. LASIK reshapes the cornea without penetrating the inside of the eye: it's not an intraocular procedure.
IOL
The abbreviation for intraocular lens implant. An artificial lens that is implanted inside the eye. IOLs are used for refractive surgery (phakic IOL implantation) or to replace the eye's natural lens if it becomes cloudy (cataract surgery).
iris
The colored ring of tissue located behind the cornea and directly in front of the lens of the eye. The central, circular opening in the iris is the pupil. The iris is what gives a person their "eye color."
Jaeger eye chart or Jaeger card
A hand-held card with six paragraphs of different-sized print that is used to test near visual acuity. The paragraph with the smallest-sized print is the J1 paragraph. The paragraph with the next larger print size is J2 and so on, until the largest paragraph (J6). The card is typically held at a testing distance of 14 inches from the viewer's eyes. Near visual acuity of J2 on the Jaeger card at a test distance of 14 inches is considered normal and the equivalent of 20/20 distance visual acuity as measured by a Snellen chart.
keratectomy
The surgical removal of corneal tissue.
keratotomy
A surgical incision (cut) of the cornea.
keratitis
Inflammation of the cornea.
kerato-
The prefix meaning "cornea" or "corneal".
keratoconus
A degenerative disorder of the eye characterized by a progressive bulging outward of the clear front surface of the eye (cornea) into an irregular cone shape.
Keratoconus (KC) often causes visual impairment that cannot be corrected with eyeglasses or contact lenses, and severe cases may require a corneal transplant to restore vision.
The National Keratoconus Foundation estimates the condition affects one of every 2,000 people in the United States.
keratomileusis
The surgical reshaping of the cornea. LASIK reshapes the cornea by removing (vaporizing) small amounts of corneal tissue with a laser.
laser
The acronym for Light Amplification by Stimulated Emission of Radiation. A laser is an instrument that produces powerful pulses of light energy that can vaporize tissue.
LASIK
LASIK is the most popular type of laser vision correction surgery. The term LASIK is an acronym for Laser In-situ Keratomileusis or Laser-assisted In-situ Keratomileusis.
The procedure involves 2 surgical steps:
- A thin flap of corneal tissue is created with a microkeratome or an IntraLase laser.
- An excimer laser is used to reshape the underlying cornea.
lens
The clear biconvex structure inside the eye (located directly behind the pupil and iris) that provides some of the eyes focusing power. About the size of an M&M chocolate candy, the lens is able to change shape, allowing the eye to focus on objects at different distances. This ability to change shape and focusing power is called accommodation. As we age, the lens becomes less flexible and the eye loses its ability to accommodate. This normal age-related loss of near focusing ability is called presbyopia and typically begins after age 40. LASIK patients who are presbyopic need reading glasses to see near objects clearly.
Meibomitis
Inflammation of glands in the eyelid (called Meibomian glands) that secrete an oily substance into the tear film to reduce the evaporation of tears. Also called Meibomianitis or Meibomian gland dysfunction (MGD), Meibomitis is a contributing cause of dry eye syndrome (DES).
Chronic inflammation of the Meibomian glands can lead to cysts in the eyelid called chalazions. Bacterial infection of a Meibomian gland is called a stye.
Treatment of Meibomitis usually consist of warm compresses, lid hygiene, and antibacterial eye drops or ointments.
Named after Heinrich Meibom, German anatomist and physician (1638-1700).
microkeratome
A precision cutting tool used to create the corneal flap in LASIK surgery. Usually refers to a mechanical microkeratome that contains a disposable oscillating blade. Recently the term laser microkeratome has been coined to describe the IntraLase femtosecond laser, a blade-free surgical device that uses laser energy to create the corneal flap. The average human cornea is about 530-540 microns thick (a little over 1/2 of a millimeter). Mechanical and laser microkeratomes used for LASIK create corneal flaps that are typically 100 to 180 microns thick.
micron
The unit used to measure corneal thickness. One micron is equal to 1/1000 of a millimeter. The central corneal thickness of the average human eye is about 530 to 540 microns---a little over 1/2 of a millimeter. (The center of the cornea is usually its thinnest point.)
monovision
The treatment of presbyopia by correcting one eye for clear distance vision and intentionally making the other eye mildly nearsighted to improve near vision (near objects will be clear, but distant objects will be blurred in this eye). Though monovision reduces the clarity of a person's distance vision to some degree, it allows older patients to see near objects quite well without reading glasses. Monovision can be performed with contact lenses or LASIK surgery.
myopia
The inability to see distant objects as clearly as near objects. Commonly called nearsightedness.
nearsightedness
The common term for myopia.
ophthalmologist
A medical doctor (M.D.) or Doctor of Osteopathy (D.O.)specializing in the diagnosis and medical or surgical treatment of vision problems and eye disease. Ophthalmologists are eye surgeons trained and licensed to perform LASIK and other types of refractive surgery.
optometrist
A Doctor of Optometry (O.D.) -- a professionally licensed eye doctor who provides routine eye care and prescribes eyewear, contact lenses, low vision aids and vision therapy for adults and children. Optometrists also may treat eye diseases---such as infections, allergic conditions and glaucoma---and provide pre-operative and post-operative care for eye surgery patients. Optometrists, however, are not licensed to perform eye surgery.
overcorrection
A complication of refractive surgery where the achieved amount of treatment is more than desired, usually resulting in a reversal of refractive error. For example, a LASIK surgery overcorrection of nearsightedness may result in the patient's refractive error changing from nearsightedness to farsightedness. Overcorrections can usually be successfully treated with a second LASIK surgery (often referred to as a LASIK enhancement).
phakic
Refers to an eye that possesses its natural lens. Phakic IOL implantation is a refractive surgery procedure that involves inserting an artificial lens inside the eye in front of the eye's natural lens.
PRK
The abbreviation for photorefractive keratectomy. PRK is similar to LASIK in that it uses an excimer laser to reshape the cornea. But a corneal flap is not created in PRK: the corneal epithelium is removed and the laser energy is applied directly to the surface of the cornea. Though outcomes with PRK are similar to LASIK, visual recovery takes longer and there may be significant discomfort for several days after PRK. For these reasons, PRK is not as popular as LASIK.
presbyopia
The normal age-related loss of near focusing ability caused by reduced elasticity of the lens inside the eye. Presbyopia usually becomes apparent after age 40. LASIK cannot reverse presbyopia, but the near vision of presbyopic patients can be improved somewhat with monovision LASIK.
punctal occlusion
The insertion of small stoppers (plugs) into the puncta–the openings of tear drainage ducts located in the upper and lower eyelids near the nose. Punctal occlusion is used to treat dry eye syndrome. By partially blocking (occluding) the drainage of tears away from the eyes, the eyes stay more moist. The plugs used for punctal occlusion can be temporary (made of a material that dissolves after several days) or permanent (made of silicone). Permanent plugs can be easily removed at a later date if necessary or they can remain in the puncta indefinitely.
pupil
The clear opening in the center of the iris that allows light to reach the retina. The pupil changes in size in response to changes in lighting: it dilates (gets larger) in dim lighting and constricts (gets smaller) in bright light. Pupil size may affect your vision after LASIK. If you have a pupil that dilates larger than the diameter of the LASIK treatment zone on the cornea, you may experience more glare at night. If you have a very small pupil, you may not be a candidate for certain types of wavefront-guided custom LASIK that have pupil size restrictions.
RK
The abbreviation for radial keratotomy, an older refractive surgery technique popular in the 1980s. RK was designed to correct myopia (nearsightedness) by flattening the cornea with radially-arranged blade cuts. Because modern LASIK surgery is safer and more effective than radial keratotomy, RK is no longer a widely-used surgical procedure.
refraction
1) The bending of light as it passes from one medium (e.g. air) to another (e.g. the cornea). 2) The test used during an eye exam to determine your eyeglasses prescription.
refractive errors
Imperfections in the focusing power of the eye. Usually refers to myopia nearsightedness), hyperopia (farsightedness) and/or astigmatism, but may also be used to describe higher order aberrations (HOA) that cannot be corrected with eyeglasses or contact lenses.
refractive power
The ability of an object (such as the cornea) to bend light as light passes through it.
retina
The fine layer of sensory tissue that lines the inner surface of the back of the eye. The retina acts like a camera photoprocessor to capture images. It transforms images into electrical signals that are sent to the visual part of the brain via the optic nerve.
sclera
The tough outer coating of the eye (the "white" of the eye) that is continuous with the clear cornea at the front of the eye.
Snellen chart
The chart of different-sized letters used to test distance visual acuity. The Snellen chart has be the standard method used to test visual acuity since the 1880s.
stereopsis
A measure of eye teaming ability important to depth perception.
stroma
The middle, thickest layer of the cornea. In LASIK, an excimer laser is used to ablate (vaporize) a small amount of stromal tissue to reshape the cornea for better vision.
undercorrection
A complication of refractive surgery where the achieved amount of treatment is less than desired. Undercorrections can usually be successfully treated with a second LASIK surgery (often referred to as a LASIK enhancement).
visual acuity
The clearness of vision; the ability to distinguish details and shapes.
wavefront
A highly-detailed computerized measurement of the total refractive errors of the eye, including higher order aberrations (HOA) that cannot be corrected with eyeglasses or contact lenses. Wavefront-assisted custom LASIK provides an added level of precision to the excimer laser treatment and therefore offers the potential for better visual acuity than standard LASIK (which uses an eyeglasses prescription to program the laser).
Last updated: March, 2010
