LASIK Glossary – Vision Correction Terms Defined
Ablate – In surgery, to remove.
Ablation – The vaporization of tissue with the Excimer laser.
Ablation zone – The area of tissue that is removed during laser surgery.
Amblyopia - The loss or lack of development of clear vision in just one eye. It is not due to eye health problems and eyeglasses or contact lenses can’t fully correct the reduced vision caused by lazy eye.
Anterior chamber – The fluid-filled area between the cornea and the lens.
Aqueous humor – The fluid in the anterior chamber.
Astigmatism – Astigmatism is an image distortion that results from an improperly shaped cornea (the front surface of the eye.) Usually the cornea is spherically shaped, like a baseball. However, in astigmatism the cornea is elliptically shaped, more like a football, i.e., there is a long meridian and a short meridian. When light passes through an astigmatic cornea it will have two points of focus, instead of one nice sharp image on the retina. This will cause the person to have blurry vision.
Automated lamellar keratoplasty (ALK) – A procedure in which the surgeon first creates a flap in the uppermost layer of the cornea using a device called a microkeratome. Then the surgeon makes an optical cut removing additional tissue with a second pass of the microkeratome. This is the predecessor of LASIK.
Axis – In ophthalmology, a line that is the symmetrical center of a curved optical surface. It gives the location of astigmatism.
Best corrected visual acuity (BCVA) – The best possible vision a person can achieve with corrective lenses measured in terms of Snellen lines on an eye chart.
Blepharitis - An inflammation of the eyelids and eyelashes causing red, irritated, itchy eyelids and the formation of dandruff like scales on eyelashes.
Cataract - A cloudy or opaque area in the normally clear lens of the eye.
Chalazion - A slowly developing lump that forms due to blockage and swelling of an oil gland in the eyelid.
Color Vision Deficiency - The inability to distinguish certain shades of colors or, in more severe cases, see colors at all.
Computer Vision Syndrome - A group of eye and vision-related problems that result from prolonged computer use.
Conjunctivitis - An inflammation or infection of the conjunctiva, the thin transparent layer of tissue that lines the inner surface of the eyelid and covers the white part of the eye.
Cornea – The front, transparent, outer-part of the eye that provides 75% of the eye’s refractive power. The cornea is approximately 500 microns thick (.5 millimeter) and consists of 5 layers epithelium, Bowman’s membrane, stroma, Descemet’s membrane and endothelium.
Corneal Abrasion - A cut or scratch on the cornea, the clear front cover of the eye.
Crossed Eyes (See Strabismus)
Diabetic Retinopathy - A condition occurring in persons with diabetes, which causes progressive damage to the retina, the light sensitive lining at the back of the eye.
Diopters – A measurement of refractive error. Hyperopia is measured in terms of positive diopters. Myopia is measured in terms of negative diopters. The most common refractive errors ranged between +6 to -6 diopters.
Dry Eye – A condition in which there are insufficient tears to lubricate and nourish the eye.
Enhancement – A secondary refractive procedure performed in an attempt to achieve better visual acuity.
Excimer Laser – A “cold” laser used in refractive surgery to reshape the corneal tissue by removing it.
Farsightedness – See Hyperopia.
Floaters & Spots - The shadowy images that are seen moving in your field of vision caused by particles floating in the fluid that fills the inside of the eye.
Glare – A condition where the patient sees additional luster around lights.
Glaucoma - A group of disorders leading to progressive damage to the optic nerve, and is characterized by loss of nerve tissue resulting in loss of vision.
Ghosting – A secondary image often with faint overlapping edges.
Halos – A condition where the patient sees additional rings around lights at night. Halos are subjective experiences that often decrease with time.
Hordeolum - An infection of an oil gland in the eyelid.
Hyperopia –A vision condition in which distant objects are usually seen clearly, but close objects do not come into proper focus.
Intraocular pressure – The pressure inside the eye.
Irregular astigmatism – A type of astigmatism in which different parts of the same meridian have different degrees of curvature or the meridians may not be 90° apart. This condition cannot be corrected with glasses. See astigmatism.
There are no terms in the Glossary for the Letter J
Keratoconous – An eye disorder causing progressive thinning and bulging of the cornea, the clear front cover of the eye.
Keratoplasty – The replacement (transplantation) of the cornea. Keratoplasty can be lamellar (replacement of superficial layers) or penetrating (replacement of the full thickness of the cornea).
Laser – An acronym for Light Amplification by Stimulated Emission of Radiation. A medical instrument that produces a powerful beam of light and can produce intense heat or cool vaporization when focused at close range. Lasers are often used in surgery to remove tissue.
LASIK - The acronym for Laser Assisted in Situ Keratomileusis. The name refers the use of a laser to reshape the cornea without invading the adjacent cell layers.
Lazy Eye- See Amblyopia.
Macula - This is a small, highly sensitive part of the retina that is responsible for detailed central vision, such as reading.
Macular Degeneration - This is an ocular disease that damages the macula of the eye and causes irreversible loss of central vision, although peripheral vision is retained. In the early stages, vision may be gray, hazy, or distorted. See Macula.
Macular Edema - This is a thickening, or swelling, of the macula of the eye. It occurs when fluid and/or protein deposits collect on or under the macula and causes distortion of the central vision. Commonly found in patients who have diabetes or macular degeneration. See Macula.
Meibomian Secretions – Oily secretions from the eyelid glands that supply the outer portion of tear film, prevent rapid tear evaporation and tear overflow.
Micron – One thousandth of a millimeter.
Microkeratome – The instrument a surgeon uses to create the corneal flap in the uppermost layer of the cornea during the LASIK procedure.
Migraine with Aura - See Ocular Migraine
Monovision – The adjustment of one eye for near vision and the other for distance vision accomplished with either corrective contact lenses or surgery.
Myopia –A vision condition in which you can see close objects clearly, but objects farther away are blurred.
Nearsightedness – See Myopia.
Nomogram – A surgeon’s adjustment to the laser’s computer calculation to further refine his or her own results.
Nystagmus - A vision condition in which the eyes make repetitive, uncontrolled movements, often resulting in reduced vision.
Ocular Allergies - The abnormal response of sensitive eyes to contact with allergens and other irritating substances.
Ocular Hypertension - An increase in the pressure inside the eye above the range considered normal, without any detectable changes in vision or damage to the structures of the eye.
Ocular Migraine - A type of severe headache accompanied by various visual symptoms.
Off label use – The permissible use of an approved drug or instrument in a way that has not been specifically sanctioned.
Optic nerve – The millions of optical nerve fibers connecting to the eye and terminating in the brain where images are created and processed.
Overcorrection – The result achieved when the change to refractive error exceeds the attempted correction, following refractive surgery.
Pachymetry – The process of measuring corneal thickness, usually using an ultrasonic probe.
Photorefractive keratotomy (PRK) – A procedure involving the removal of the surface layer of the cornea (epithelium) followed by use of an Excimer laser to reshape the stroma. Acronym is PRK.
Pinquecula - An abnormal growth of tissue on the conjunctiva, the clear membrane that covers the white of the eye.
Plano – Indicated there is no refractive error.
Presbyopia – An age-related vision condition in which there is a gradual loss of the eye’s ability to focus on near objects.
Pterygium - An abnormal growth of tissue on the conjuctiva, the clear membrane that covers the white of the eye, and the adjacent cornea, the clear front surface of the eye.
There are no terms in the Glossary for the Letter Q
Radial keratotomy (RK) – A surgical procedure designed to correct myopia (nearsightedness) by flattening the cornea with incisions. The procedure is called radial keratotomy because the incisions resemble the spokes in a wheel. Acronym is RK.
Refraction – The bending of light waves as they pass from one medium to another. This is measured in an eye exam to determine the optimal lenses for vision.
Refractive surgery – Any surgical procedure that attempts to decrease the patient’s refractive error. Typically the surgeon alters the shape of the cornea in order to change the angle at which an image is projected onto the retina. Such procedures include RK, PRK, and LASIK.
Regression – A backwards shift from the initial visual outcome, following refractive surgery.
Regular astigmatism – A type of astigmatism where the curvature in each meridian is equal throughout its length. Also, the meridians of greatest and least curvature are at right angles to each other. See astigmatism.
Retina – Light processing membrane; converts light into electrical impulses that are transmitted to the optic nerve.
Retinal Detachment - A tearing or separation of the retina, the light sensitive lining at the back of the eye, from the underlying tissue.
Slit lamp – Table-top microscope for examining the eye.
Snellen chart – An eye chart used to test a patient’s vision.
Strabismus - A condition in which the eyes are misaligned.
Stye - See Hordeolum.
Subconjunctival Hemorrhage - An accumulation of blood underneath the conjunctiva, the clear membrane covering the white part of the eye.
Symmetry of refractive error – The refractive error in both eyes are close to the same value.
Tear film – A very thin film of oil, salt water, and mucin riding on top of the epithelium that lubricates the front of the eye.
Uncorrected visual acuity (UCVA) – A person’s vision without corrective lenses measured in terms of Snellen lines on an eye chart. Acronym is UCVA.
Undercorrection – The result achieved when desired change in refractive error is not fully achieved, following refractive surgery.
Uveitis - An inflammation of one or more of the structures that make up the middle layer of the eye called the uvea.
Vitreous humor – The gel-like fluid in the main cavity of the eye behind lens and pupil that accounts for 80% or the eye’s volume.
There are no terms in the Glossary for the Letter W
There are no terms in the Glossary for the Letter X
YAG Laser - YAG is an acronym for neodymium Yttrium-Aluminum-Garnet, which is the material used to create this laser. It’s used after cataract surgery to vaporize scar tissue.
YAG Laser Capsulotomy - After cataract surgery, your vision can become cloudy, like it was when you had a cataract. But it isn't a new cataract; instead, the posterior capsule, which holds the lens in place, becomes cloudy and may blur your vision. This is called an after-cataract, and can develop months or even years after your surgery. Unlike a cataract, an after-cataract is treated with a laser. In a painless out-patient procedure called YAG laser capsulotomy, your doctor uses a laser beam to make a tiny hole in the posterior capsule to let light pass through.
There are no terms in the Glossary for the Letter Z