Eye Glossary Including LASIK
20/20 Vision the first 20 refers to the testing distance of 20 ft The second 20 refers to the size of the letters on the chart. Most normal eyes see this line and thus have 20/20. The large top letter (the “E”) on the chart is called the 200 line and if that is all a patient can see the vision is recorded as 20/200. The person with 20/20 vision could identify this large “E” at 200 feet whereas the person with 20/200 can only see it at 20 feet.*
Aberrometry the measurement of the imperfections in the optical system of the eye, measured in microns as root mean square (RMS). The use of aberrometry in developing better lens systems for telescopes is called adaptive optics and has been used by astronomers for years. It has only recently been applied to the eye.*
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.
Anesthesia is medication that attempts to eliminate pain impulses from reaching the brain. In general anesthesia this is accomplished by putting the patient asleep. Most eye surgery is accomplished by local anesthesia with drops or injections of anesthetic medications either directly applied to the eye or injected around the eye.*
Aqueous Humor the clear fluid between the anterior chamber of the eye (which is the space between the cornea and the lens). It is continually produced by the ciliary body, the part of the eye that lies just behind the iris.
Astigmatism a distortion of the image on the retina caused by irregularities in the cornea or lens. Regular astigmatism causes light rays to come to a focus at two separate points, 90 degrees apart, rather than at one point as occurs in eyes that focus without astigmatism.
Bifocals eyeglasses with two lenses for each frame. With bifocals, the most convex lenses (for close viewing) are in the lower half of the frame and the least convex lenses on the upper for distance vision.*
Blended Vision the medical term for Monovision, which is the purposeful adjustment of one eye for near vision and the other eye for distance vision.
Cataracts An opacity (clouding) in the internal natural lens of the eye. Most patients will eventually develop cataracts as they age but not all cataracts interfere with vision and so they do not all have to be removed.*
Choroid a layer of blood vessels and connective tissue between the sclera (white of the eye) and retina that nourishes the inner part of the eye.*
Ciliary Body is composed of ciliary muscles and processes. The ciliary processes produces nutrients for the eye such as the Aqueous Humor. The ciliary muscles assist in accommodation or focusing of the eye for vision. When the ciliary muscle relaxes, it flattens the lens, generally improving the focus for farther objects. When it contracts, the lens becomes more
convex (curved), generally improving the focus for closer objects.*
Clear Lensectomy (CLE) also referred to as Refractive Lensectomy (RLE). The removal of the natural lens of the eye even though it does not have a cataract to replace it with an artificial lens implant of the proper power to correct nearsightedness or farsightedness in patients not suitable for LASIK or PRK. *
Conductive Keratoplasty (CK) Focal application of radio frequency energy, usually in 8 or 16 spots to shrink the corneal collagen so as to increase the central curvature of the eye so provide better reading vision in normal sighted or post LASIK patients who have good distance vision but have become presbyopic as they aged.*
Conjunctiva a thin membrane that covers the sclera (the white part of the eye) and lines the inside of the eyelids.
Contact Lenses (or "Contacts") a corrective or therapeutic lens usually placed on surface of the eye. Contact lenses usually serve the same corrective purpose as conventional glasses.*
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.
Diopter the measurement of refractive error. A negative diopter value signifies an eye with myopia and positive diopter value signifies an eye with hyperopia. (The term Diopter is commonly referred to with a “d”, so as an example, a prescription would read “+2.25D” or “+2.25 d”).*
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.
Emmetropia perfect vision, which is occurs when a normal eye focuses rays of light exactly on the retina. An eye in a state of emmetropia requires no correction.*
Endothelium the inner layer of cells on the inside surface of the cornea.
EpiLasik a form of PRK where the epithelim is removed with a mechanical microkeratome and the underlying surface is then treated with an excimer laser.*
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.
Farsightedness the common term for hyperopia, which is the ability to see distance objects more clearly than near objects. Mild farsightedness in young patients is compatible with good vision through accommodation.*
FDA the abbreviation for the Food and Drug Administration. It is the United States governmental agency responsible for the evaluation and approval of medical devices.
Flap & Zap a slang term for LASIK.
Ghost Image a fainter second image of the object you are viewing.
Glare scatter from bright light that decreases vision.
Glaucoma an increase in the normal pressure of the eye which will eventually damage the optic nerve of the eye resulting in loss of vision.*
Halos rings around lights due to optical imperfections in or in front of the eye.
Haze corneal clouding that causes the sensation of looking through smoke or fog.
Higher order aberrations refractive errors, other than nearsightedness, farsightedness, and astigmatism, that cannot be corrected with glasses or contacts. Higher order aberrations are present to varying degrees in all eyes and are often increased by laser refractive surgery. The two most common HOA’s are coma, which causes a comet or tail like flare off of lights at night and spherical aberration which can cause a glow or halo around lights.*
Hyperopia the medical term for farsightedness, which is the ability to see distance objects more clearly than near objects. Mild farsightedness in young patients is compatible with good vision through accommodation.*
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.
In Situ a Latin term meaning "in place" or not removed.
Iris the colored ring of tissue suspended behind the cornea and immediately in front of the lens.
IntraLase (femtosecond laser) a laser which fires at an exceptionally fast rate (e.g. 60,000 pulses per second) at a wavelength which does not heat or damage tissue. The IntraLase laser is currently the most commonly used procedure because it more safely and precisely assists in the creation create of LASIK flaps without the use of a blade.*
Intraocular inside the eye. For example, Toric Implants are intraocular lens implants (which are inserted inside the eye). *
Intraocular Lens (IOL) a lens that is inserted inside the eye. For example, Phakic Implants are intraocular lens implants which are inserted inside the eye (between the cornea and the lens).*
Keratectomy the surgical removal of corneal tissue.
Keratotomy a surgical incision (cut) of the cornea.
Keratitis inflammation of the cornea.
Kerato prefix indicating relationship to the cornea.
Keratoconus a disorder characterized by an irregular corneal surface (cone-shaped) resulting in blurred and distorted images.
Keratomileusis carving of the cornea to reshape it.
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.
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.
LASEK (Laser-Assisted Sub-Epithelial Keratectomy) a form of PRK where the epithelium is loosened, usually with alcohol, and either reflected like a LASIK flap and replaced after the excimer laser is applied to reshape the cornea. At times the epithelium is simple discarded and allowed to regenerate as it does in standard PRK surgery.*
Lens a part of the eye that provides some focusing power. The lens is able to change shape allowing the eye to focus at different distances.
Lower Order Aberrations refractive errors, such as nearsightedness, farsightedness, and astigmatism, that typically can be corrected with LASIK, PRK, other laser vision correction procedures, as well as glasses or contact lenses.
Mechanical Microkeratome a surgical instrument like a miniature carpenter’s plane with a vibrating metal blade and depth plate used to create the flap in LASIK surgery. *
Microkeratome a surgical device 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 the inability to see distant objects as clearly as near objects. Myopia is the medical term for nearsightedness. *
Nearsightedness the common term for myopia, which is the inability to see distant objects as clearly as near objects. *
NearVision CK (Conductive Keratoplasy) “Nearvision” refers to the specific patented and FDA-approved procedure. CK (Conductive Keratoplasy) is the focal application of radio frequency energy, usually in 8 or 16 spots to shrink the corneal collagen so as to increase the central curvature of the eye so provide better reading vision in normal sighted or post LASIK patients who have good distance vision but have become presbyopic as they aged.*
Ophthalmologist a medical doctor specializing in the diagnosis and medical or surgical treatment of visual disorders and eye disease.
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.
Phakic Implants a type of IOL (Inter Ocular Lends) that is inserted between the cornea and the lens inside the eye for the purpose of correcting near or farsightedness where LASIK is contraindicated.*
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.
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
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 Lensectomy (RLE) also referred to as Clear Lensectomy (CLE). The removal of the natural lens of the eye even though it does not have a cataract to replace it with an artificial lens implant of the proper power to correct nearsightedness or farsightedness in patients not suitable for LASIK or PRK. *
Refractive Errors imperfections in the focusing power of the eye, for example, hyperopia, myopia, and astigmatism.
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, 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.
Visual Acuity Chart one of many charts used to measure vision.
Visian ICL a type of Phakic Lens manufactured by STAAR Surgical. The STAAR Visian ICL (Implantable Collamer Lens) may be used for correction of Nearsightedness (Myopia). It is placed behind the pupil just in front of the eyes natural crystalline lens.*
Stigmata a physical mark or peculiarity which may aid in the identification or diagnosis of a condition*
Stroma the middle, thickest layer of tissue in the cornea.
Toric Implants a type of Intraocular Lens (IOL) used to correct astigmatism.*
Undercorrection a complication of refractive surgery where the achieved amount of correction is less than desired.
Verisyse(tm) Implant Advanced Medical Optics (AMO) makes the VerisisyseTM Phakic Implant for correction of high myopia (nearsightedness). This lens clips to the iris like a “lobster claw".
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 and fills the center of the eyeball.
Wavefront a measure of the total refractive errors of the eye, including nearsightedness, farsightedness, astigmatism, and other refractive errors that cannot be corrected with glasses or contacts.
Wavefront Guided LASIK or PRK is LASIK or PRK refractive surgeries based on aberrometry measurements and is designed to treat the refractive error of the eye while minimizing the induction of higher order aberrations. All eyes have aberrations. Lower order aberrations represent the prescription for glasses to correct vision. If a patient has natural 20/20 vision or better the eye will have essentially no lower order aberrations but will still have higher order aberrations.*
The definitions provided in the glossary are provided courtesy of the Federal Drug Administration (“FDA”), except for those marked with an asterisk (*), which have been modified or added to the Glossary by Trusted LASIK Surgeons.
To visit the FDA website, please go to www.fda.com
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