At East Valley Ophthalmology, we take pride in sharing information about eye care. Below is a list of common eye-related medical terminology and definitions to help you understand all aspects of your eye care and eye surgery.
Glossary of Eye Care Terms
Aberration: Distortions related to astigmatism cause the inability of light rays entering the eye to converge (come together) to a single focus point on the retina. Aberration is divided into two main categories: higher-order and lower-order.
Ablation: Surgical removal of tissue, typically using a cool beam laser.
Ablation zone: The area of tissue that is removed during laser surgery.
Accommodation: The Ability of the eye to change its focus between distant and near objects.
Acuity: Sharpness, acuteness, or keenness of vision.
Acute: Occurring suddenly.
Adnexa: Accessory structures of the eye, including the eyelids, lacrimal apparatus, etc.
AK: Astigmatic Keratotomy, a modified form of Radial Keratotomy (RK).
Amblyopia: Dullness or obscurity of sight for no apparent organic reason; therefore, it is not correctable with glasses or surgery. Sometimes called a lazy eye, this condition occurs when one eye becomes dependent on the other to focus, typically developing in early childhood and often associated with strabismus.
Amsler grid: Hand-held chart featuring horizontal and vertical lines, usually white on a black background, used to test for central visual field defects.
Angle: The drainage area of the eye formed between the cornea and the iris, named for its angular shape, which is why you see the word “angle” in the different glaucoma names.
Anisometropia: Condition of the eyes in which they have unequal refractive power.
Anterior chamber: Space between the cornea and the crystalline lens, which contains aqueous humor.
Anterior ocular segment: Part of the eye anterior to the crystalline lens, including the cornea, anterior chamber, iris, and ciliary body.
Antioxidants: Micronutrients that destroy or neutralize free radicals, molecules implicated as one causative factor in stimulating abnormal cellular reproduction (cancer) and cellular destruction (aging).
Antireflective coating: Coating on the front or back of glasses lenses, which minimizes the glare for patients who are highly bothered by glare.
Aphakia: Absence of the lens of the eye.
Aqueous humor: Transparent fluid that occupies the anterior chamber and maintains eye pressure.
Argon laser: A device used to treat glaucoma (usually open-angle) and diabetic retinopathy using a thermal beam.
ARMD: Age-related macular degeneration: Destruction and loss of the photoreceptors in the macula region of the retina, resulting in decreased central vision and, in advanced cases, blindness.
Asthenopia: Eyestrain.
Astigmatic Keratotomy (AK): Treats astigmatism by flattening the cornea with arc-shaped incisions in its periphery, similar to RK.
Astigmatism: Structural defects of the eye in which the light rays from a viewed object do not meet in a single focal point, resulting in blurred images sent to the brain. An astigmatic cornea is not perfectly rounded like a basketball but has an irregular shape that is more like the side of a football. Astigmatism is most often combined with myopia or hyperopia.
Automated Lamellar Keratoplasty (ALK): This procedure predates LASIK eye surgery and is not generally used anymore.
Automated perimeter: A computer-driven device plotting defects in the visual field (peripheral or side vision). Usually, this is a large hemisphere shell into which the patient’s head is placed. Various points of light, sometimes of different sizes, intensities, and colors, are projected onto the screen. The patient then indicates whether they see the light, and the response is recorded. The computer then plots the effective visual thresholds within the targeted visual field.
Axis: Optical – a straight line through the centers of both lens surfaces. Visual – a straight line from the object of vision to the eye’s fovea.
BCVA: Best corrected visual acuity.
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.
Beta-carotene: Member of the carotenoid family of vitamins, a precursor to vitamin A, thought to be beneficial to the eyes and helpful in treating diseases such as glaucoma.
Bifocals: Lenses containing two focal lengths, usually arranged with the focus for distance above and near focus below.
Binocular vision: Simultaneous use of the two eyes. Normal binocular vision yields a stereoscopic image and parallax-induced depth perception.
Blepharitis: Inflammation of the eyelids, a common condition that tends to recur.
Blind spot: The area of the optic disk where the optic nerve fibers exit the eye and where there are no light-sensitive cells. This small area can be measured, and in glaucoma, as the nerve fibers die, the blind spot tends to enlarge and elongate. This is one of the diagnostic hallmarks of glaucoma.
Bowman’s membrane: An extremely thin second layer of the cornea, situated between the epithelium and stroma, thought to be responsible for epithelium adhesion.
Capsular haze: A thin film of scar tissue that occasionally forms on the posterior capsule behind the intraocular lens implant following cataract surgery and is removed with an Nd:Yag laser.
Caruncle: Small, red portion of the eye’s corner containing modified sebaceous and sweat glands.
Cataract: Gradual clouding of the crystalline lens resulting in reduced vision or eventual blindness, correctable by cataract surgery.
Cataract surgery: Removal of a Cataract, replacing it with an intraocular lens implant.
Central islands: Central islands are small mounds of central tissue that can interfere with vision and occur when the laser beam does not uniformly remove tissue in the center of the treatment area.
Choroid membrane: Dark, vascular, thin skin-like tissue between the sclera and the retina, forming the middle coat of the eye. The choroid membrane nourishes the outer portions of the retina and absorbs excess light.
Chronic: It is of long duration and persists for an extended period.
Closed-angle glaucoma: Glaucoma conditions occur suddenly (acute).
Ciliary body: Part of the eye that connects the choroid membrane to the iris. Produces aqueous humor that fills the front part of the eye and maintains eye pressure.
Ciliary muscle: The muscle attached to the crystalline lens is responsible for focus (the same as the ciliary body, but used in a different context).
Clear Lens Extraction (CLE): This procedure involves removing the eye’s natural, clear crystalline lens and replacing it with an intraocular lens implant, using the same technique as cataract surgery.
Colorblindness: Inaccurate term for a lack of perceptual sensitivity to specific colors. Absolute color blindness is almost unknown.
Color vision: Ability to perceive differences in color, including hue, saturation, and brightness.
Comprehensive eye exam: Evaluation of the complete visual system.
Conductive Keratoplasty (CK): A procedure in which a radio frequency probe, rather than a laser, is used to reshape the cornea. It is approved for low to moderate hyperopia in patients over age 40; however, it does not appear to have the precision of LASIK.
Cones: One of the two types of light-sensitive cells concentrated in the center of the retina (also see rods). There are about 6.5 million cones in each eye – 150,000 cones in every square millimeter – responsible for detailed visual acuity and the ability to see in color.
Conjunctiva: Mucous membrane lining the inner surface of the eyelids and covering the front part of the sclera (white part of the eye), responsible for keeping the eye moist.
Conjunctivitis: Inflammation or irritation of the conjunctiva. Symptoms can be present in just one eye or affect both eyes, including redness of the eyes or the edges of the eyelids, swelling of the eyelids, or itching.
Contact lens: Small, thin, removable plastic lens worn directly on the front of the eyeballs, usually used instead of ordinary eyeglasses for correction or protection of vision.
Convergence: Turning the eyes inwards so they are both “aimed” towards a near object being viewed. Usually, it works in harmony with divergence, which is used for more distant objects.
Cornea: Transparent tissue that forms the front part of the eyeball, covering the iris and pupil. The cornea is the first part of the eye that bends (or refracts) the light and provides most of the focusing power.
Corneal curvature: Shape of the front of the eye.
Corneal mapping, topography: A tool used to see the refractive problems that might be present in the cornea. Corneal topography is used not only for screening all patients before refractive surgery, such as LASIK, but also for fitting contact lenses.
Corneal relaxing incisions (CRIs): True corneal incisions, such as RK and AK.
Corneal transplant (penetrating keratoplasty): Surgical grafting of a replacement cornea onto an eye.
Crystalline lens: Double convex, transparent eye part located behind the iris and in front of the vitreous body. It connects with the cornea to refract incoming light rays onto the retina.
Cylinder: Refers to the degree of astigmatism (uneven roundness) in the cornea.
Depth perception: The vision system’s ability to perceive objects’ relative positions in the visual field.
Detached retina: A retinal detachment occurs when the retina is pulled away from its normal position in the back of the eye.
Diabetes mellitus: Chronic metabolic disorder characterized by a lack of insulin secretion and/or increased cellular resistance to insulin, resulting in elevated blood levels of simple sugars (glucose) and including complications involving damage to the eyes, kidneys, nervous system, and vascular system
Diabetes type I (IDDM): Insulin-dependent, resulting from the destruction of the insulin-producing pancreatic islet cells
Diabetes type II (NIDDM): Non-insulin dependent, resulting from tissue resistance to insulin
Diabetic retinopathy: Deterioration of retinal blood vessels in diabetic patients, possibly leading to vision loss.
Dilated, dilation: Enlargement of the pupil (space in the middle of the iris).
Diopter: Unit of measure of the refractive power of an optical lens (equal to the power of a lens with a focal distance of one meter). A negative diopter value (such as -3D) signifies an eye with myopia, and a positive diopter value (such as +3D) signifies an eye with hyperopia.
Diplopia: Condition in which a single object is perceived as two; also called double vision.
Divergence: Turning the eyes outwards so that they are both “aimed” towards the object being viewed. Usually, it works in harmony with convergence.
Double vision: Same as diplopia.
Dry eye: A common condition that occurs when the eyes do not produce enough tears to keep the eye moist and comfortable.
Emmetropia: Twenty-twenty vision.
Endothelium: Cellular tissue that covers the inner surface of the eye within the closed cavity, typically referring to the cornea.
Enhancement: An additional LASIK procedure is used to refine Personal Best Vision.
Epithelium: Cellular tissue that covers the outer surface of the eye. Consists of one or several layers of cells with only a little intercellular material.
Esophoria: The eyes are in an over-converged position compensated by the external eye muscles so that the eyes do not appear to be turned inward.
Esotropia: The eyes are placed in an over-converged position to turn the non-fixating eye inward. One eye looks straight; one looks inward.
Excimer laser: a laser used in LASIK surgery that operates in the ultraviolet wavelength, producing a cool beam.
Exophoria: The eyes are in an over-diverged position compensated by the external eye muscles so that the eyes do not appear to be turned outward.
Exotropia: The eyes are positioned over-diverged to turn the non-fixating eye outward. One eye looks straight ahead, and one turns outward.
Extracapsular cataract surgery: Surgery in which the Cataract is removed in one piece through a larger incision, which usually requires several stitches.
Extraocular muscles: Six muscles that control eye movement. Five originate from the back of the orbit; the other one originates from the lower rim of the orbit. Four move the eye up, down, left, and right; the other two control the twisting motion of the eye when the head tilts. All six muscles work in unison; the condition is called strabismus when they do not function properly.
Eye chart: A Snellen chart is a printed visual acuity chart consisting of Snellen optotypes, which are specifically formed letters of the alphabet arranged in rows of decreasing letter size.
Eyelid: Either of two movable, protective folds of flesh that cover and uncover the front of the eyeball.
Farsighted: Common term for hyperopia.
FDA: Abbreviation for the Food and Drug Administration. It is the United States governmental agency responsible for evaluating and approving medical devices.
Femtosecond laser: Used in the IntraLASIK procedure to create a safer and more precise flap than the older mechanical microkeratome technology, it employs a longer wavelength, a smaller spot, and a shorter duration per pulse than the excimer laser used to reshape the cornea.
Field of vision: The entire area can be seen without needing to shift the gaze.
Flap: Part of the cornea consists of the epithelium, Bowman’s membrane, and some stroma, cut with a remaining hinge and lifted as part of the LASIK procedure.
Flashes & floaters: Light spots or streaks and dark moving specks due to the vitreous traction on the retina (light flashes) and solid vitreous material or blood (floaters).
Fluorescein angiography: Diagnostic test by which the veins deep inside the eye are examined. Dye is injected into a vein in the arm and circulated through the blood to the back of the eye, allowing for a visual examination.
Fovea: Small depression in the retina, the point where vision is most acute.
Fundus: The first point at the back of the eye, consisting of the retina, choroid membrane, sclera, optic disc, and blood vessels, is seen using the ophthalmoscope.
Ghost image: A faint second image of the object you are viewing.
Giant papillary conjunctivitis: A type of conjunctivitis wherein bumps or ridges form on the inside of eyelids, which make wearing contact lenses uncomfortable; in fact, this condition is often caused by over-wearing of specific contact lenses
Glare: Scatter from bright light that decreases vision.
Glaucoma: A painless eye disease characterized by increased pressure within the eye; left untreated, it leads to a gradual impairment of sight, often resulting in blindness.
Gonioscopy: A viewing procedure that utilizes a mirror/lens device placed directly on the cornea to view the drainage area, known as “the angle,” through which aqueous fluid exits the eyeball.
Halos: Rings around lights due to optical imperfections in, or in front of, the eye.
Haptics: The arms of an intraocular lens hold it in place once inserted inside the eye.
Haze: Corneal clouding that causes the sensation of looking through smoke or fog.
Heterophoria: Constant tendency of one eye to deviate in one or another direction due to the imperfect balance of ocular muscles.
Holmium laser: A laser that operates in the infrared wavelength, producing a hot beam. It is used in Laser Thermokeratoplasty Surgery and more commonly in surgical procedures involving the disintegration of stones and the ablation of fibrous tissue.
Hyperopia, also known as farsightedness, is the inability to see near objects as clearly as distant objects, requiring accommodation to focus on distant objects.
Hypoxia: Deficiency of oxygen supply to a tissue.
Image: Light reflected into the eye, off objects in front of the eye. This light contains all the information about the objects (such as color, shadow, motion, and detail) that is translated to the brain and allows you to “see” (know about) the objects.
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: Document disclosing the risks, benefits, and alternatives to a procedure.
In Situ: Term meaning “in place.”
Intracapsular cataract surgery: Cataract surgery in which both the lens and capsule are entirely removed – a rarely used procedure.
Intraocular lens implant (IOL): Permanent, artificial lens surgically inserted inside the eye to replace the crystalline lens following cataract surgery or clear lens extraction.
Intraocular pressure (IOP): Fluid pressure within the eye created by the continual production and drainage of aqueous fluid in the anterior chamber.
Iridotomy: Treatment for closed-angle glaucoma, one of the many types of glaucoma, usually done with a laser.
Iris: Colored part of the eye. Elastic, pigmented, muscular tissue in front of the crystalline lens regulates the amount of light entering the eye by adjusting the pupil size in the center.
Ischemia: Restriction or blockage of blood flow through a blood vessel. Ischemia is a causative agent of specific heart attacks and strokes and is involved in various types of visual field losses.
Intacs: Surgically implanted plastic half rings that change the shape of the cornea.
Keratectomy: Surgical removal of corneal tissue.
Keratitis: Inflammation of the cornea
Keratotomy: Surgical incision (cut) of the cornea.
Keratoconus: Rare, serious, degenerative corneal disease in which the cornea thins and assumes the shape of a cone.
Keratomileusis: Carving of the cornea to reshape it.
Keratoplasty: Surgical reshaping of the cornea.
Lacrimal apparatus: Part of the eye that produces tears.
LASEK: laser Epithelial Keratomileusis, a refractive surgery in which the epithelium is cut with a fine blade, called a trephine, and involves displacing the corneal epithelium as a sheet and then replacing it to (theoretically) act as a natural bandage.
Laser: A device that generates an intense and highly concentrated light beam. Acronym for: Light Amplification by Simulated Emission of Radiation. (Also see: holmium laser, argon laser, Nd:Yag laser, femtosecond laser, and excimer laser)
Laser Thermokeratoplasty (LTK): A holmium ‘hot’ beam laser, rather than the ‘cool’ beam excimer laser, is used to treat farsighted patients, but its application is limited due to the effects not being long-lasting.
LASIK: Laser-Assisted In-Situ Keratomileusis, a refractive surgery in which Excimer laser ablation is performed under a flap on the cornea to correct refractive errors.
Lazy eye: Amblyopia, an eye condition characterized by reduced vision that is not correctable with glasses or contact lenses, is not typically caused by an underlying eye disease.
Legally blind: 20/200 vision and over is the qualification of legal blindness in the United States.
Lens: Same as the crystalline lens. Double convex, clear part of the eye, behind the iris and in front of the vitreous humor. It refracts the various light rays to form an image on the retina.
Lenticular: Special non-cataract lenses for patients who have cataracts.
Lid speculum: A surgical tool that holds the eyelids open and allows the surgeon to access the eye with minimal pressure on the globe.
Limbal relaxing incisions (LRI): Small incisions placed on the far peripheral aspect of the cornea, resulting in a rounded cornea for correcting astigmatism.
Limbus: Thin area that connects the cornea and the sclera.
Low vision occurs when ordinary eyeglasses or contact lenses cannot restore a patient’s sight to normal sharpness.
LTK (Laser Thermal Keratoplasty): A holmium ‘hot’ beam laser, rather than the ‘cool’ beam excimer laser, is used to treat farsighted patients, but its application is limited due to the effects not being long-lasting.
Lutein: Member of the carotenoid family of vitamins, similar to beta-carotene, thought to be beneficial to the eyes and helpful in treating diseases such as glaucoma.
Macula: Yellow spot on the retina, where the photoreceptors are most dense and responsible for the central vision. It has the greatest concentration of cones, which are responsible for visual acuity and the ability to see in color.
Macular edema: Collection of fluid in and under the macular portion of the retina.
Macular degeneration: Disease of the macula, which results in the loss of central vision.
Meridian: Orientation of a particular curve, often used concerning the cornea.
Microkeratome: A mechanical surgical device affixed by a vacuum ring to the eye. When secured, a sharp blade cuts a layer of the cornea at a predetermined depth.
Miosis: Pupillary constriction.
Monovision: Purposeful adjustment of one eye for near vision and the other for distance vision.
Mydriasis: Pupillary dilation.
Myopia: Also called nearsightedness or shortsightedness, the inability to see distant objects as clearly as near objects.
Near point of accommodation: The closest point in front of the eyes at which an object may be clearly focused.
Near point of convergence: The Maximum extent to which the two eyes can be turned inwards.
Nearsighted: Common term for myopia.
Neodymium YAG Laser: Laser used to treat Posterior Capsular Opacification (PCO) and open-angle glaucoma. Selective Laser Trabeculoplasty
Neovascularization: Often associated with diabetes, it involves the formation of new blood vessels that are often fragile and inappropriate for their location.
Nerve fibers/axons: Extensions of photoreceptors that form the nerve bundle called the optic nerve.
Neuro-ophthalmology: Subspecialty that treats the nervous and vascular systems that involve the eye.
Normal vision: Occurs when light is focused directly on the retina rather than in front of or behind it.
Ocular herpes: A recurrent viral infection caused by the herpes simplex virus. Ocular herpes represents the most common infectious cause of corneal blindness in the United States.
Ocular hypertension: Elevated fluid pressure. Normal pressure is about 10 to 21 mmHg, with most people falling between 13 and 19 mmHg. Over 21 is considered suspicious. Over 24, cautiously concerned, warranting immediate investigation. Over 30 is considered urgent and a potential emergency.
OD: Abbreviation for “oculus dextrum,” meaning right eye.
ONH: Optic nerve, optic nerve head. A bundle of nerve fibers about the diameter of a pencil passes through the back of the eyeball and connects to the nerve fiber layer of the retina. It can be observed directly with an instrument called an ophthalmoscope.
Open-angle glaucoma: Glaucoma conditions have a long duration (chronic).
Ophthalmologist: An ophthalmologist is either a medical doctor (MD) or an osteopathic physician (D.O.) who is qualified and specially trained to diagnose and treat all eye and visual system problems, medically and surgically, and diagnose general diseases of the body.
Ophthalmoscope: An instrument used to examine the interior of the eye, consisting of a perforated mirror arranged to reflect light from a small bulb into the eye.
Ophthalmoscopy: Examination of the eye’s internal structures using an illumination and magnification system.
Optic disc: The head of the optic nerve is formed by the meeting of all retinal nerve fibers.
Optic nerve: Bundle of nerve fibers that connects the retina with the brain. The optic nerve carries signals of light to the area of the brain called the visual cortex, where the signals are assembled into images, allowing for vision.
Optician: Expert who designs, verifies, and dispenses lenses, frames, and other fabricated optical devices upon the prescription of an ophthalmologist or an optometrist.
Optometrist: Eye care professional, an optometry school graduate, provides non-surgical visual care. Specifically educated and trained to examine the eyes, determine visual acuity, and diagnose other vision problems and ocular abnormalities. An optometrist prescribes glasses and contact lenses to improve visual acuity.
Orbit: Bony socket containing the eyeball, fat, extraocular muscles, nerves, and blood vessels.
Orthokeratology (OK): Non-surgical procedure using contact lenses to alter the shape of the cornea to effect a change in the refractive error.
Orthoptics: Exercises designed to help the eye muscles work together to improve visual perception.
OS: Abbreviation standing for “oculus sinister,” meaning left eye
Overcorrection: Occurrence in refractive surgery where the achieved amount of correction is more than desired; in LASIK, typically due to a patient’s over-response to the laser ablation.
Pachymeter: An instrument that measures the distance between the top of the corneal epithelium and the bottom of the corneal endothelium. It is used as a diagnostic testing device to measure corneal thickness.
Pachymetry: A test used to measure corneal thickness.
Papilledema: Noninflammatory swelling/elevation of the optic nerve often due to increased intracranial pressure or space-occupying tumor.
PD: Used on prescriptions to indicate the distance between the pupils of both eyes.
Pellucid marginal degeneration: A bilateral, noninflammatory, peripheral corneal thinning disorder characterized by a peripheral band of thinning of the inferior cornea.
Peripheral vision: Ability to perceive objects’ presence, motion, or color outside the direct line of vision.
Personal Best Vision: Best possible vision for each individual as corrected.
Phacoemulsification cataract surgery: The cataract removal procedure involves making a tiny incision about 1/8″ long. A pen-like instrument, inserted through the opening, is used to emulsify and aspirate the clouded lens material using gentle sound waves. Then, an intraocular lens is inserted into place.
Phacofracture cataract surgery: Cataract surgery in which the lens is removed through a small incision by “fracturing” it into several small segments, rarely used today.
Phakic Intraocular Lenses (IOLs): Placed inside the eye without removing the natural lens, and perform much like an internal contact lens.
Phoropter: A standard device found in most eye doctors’ offices, with multiple lenses, used to measure refractive errors. A phoropter calculates the prescription required for corrective lenses.
Photocoagulation: Focusing powerful light rays onto tiny spots on the back of the eye produces heat, which seals retinal tears and cauterizes small blood vessels.
Photophobia: Sensitivity to light.
Photoreceptors: Microscopic light-sensitive cells located in the retina, called rods and cones. The human eye has approximately 7 million cones and 125 million rods.
Photo Refractive Keratectomy (PRK): Surgery in which a small area on the corneal epithelium (surface cells) is gently polished away. The laser then reshapes the corneal surface in the same way as for LASIK surgery.
Pingecula: Irritation causes degeneration of the conjunctiva, resulting in a thickening and yellowing of the normally thin, transparent tissue.
Pink eye: A type of conjunctivitis commonly seen in children.
Posterior capsule: The thin membrane in the eye that holds the crystalline lens in place.
Posterior chamber: The back section of the eye’s interior.
Posterior optical segment: Part of the eye posterior (behind) to the crystalline lens, including the vitreous, choroid, retina, and optic nerve.
Posterior Vitreous Detachment (PVD): Separation of the vitreous body from its attachment to the retinal surface due to shrinkage from degenerative or inflammatory conditions or trauma. An age-related condition.
Prelex: Surgical procedure that attempts to correct presbyopia.
Presbyopia: Inability to maintain a clear image (focus) as objects are moved closer. Presbyopia is caused by the reduced elasticity of the lens with increasing age.
Prescription: Amount of vision correction necessary, written in a form that can be utilized during the manufacture of corrective lenses or to configure a laser machine.
PRK: Acronym for Photo-Refractive Keratectomy, a procedure involving removing the cornea’s ( epithelium) ‘s surface layer by gentle scraping and using a computer-controlled excimer laser to reshape the stroma.
Progressive lenses: Bifocal or trifocal lenses that appear as single vision with no distinct lines between the focal lengths.
Punctal occlusion: Treatment for dry eye in which plugs are inserted into the punctum to retain lubricating tears naturally produced by the eye.
Punctum: The hole in the upper and lower eyelids through which tears exit the eye. In patients with dry eyes, temporary or permanent plugs may be inserted to help keep tears in the eye. Tears flow through the punctum to the nose, so people often experience a runny nose when crying.
Pupil: Black circular opening in the center of the iris through which light passes into the crystalline lens. It changes size in response to the amount of light received by the eye, becoming larger in dim lighting conditions and smaller in brighter ones.
Pupillary response: Constriction and dilation of the pupil due to stimulation by light or accommodation.
Radial Keratotomy (RK): This outdated procedure was once used to correct mild to moderate myopia, making a series of spoke-like incisions around its periphery to flatten the cornea.
Refract: To bend aside, as in “the crystalline lens refracts the light as it passes through,” or to measure the degree the eyes or lenses bend light, as in “the doctor refracts a patient’s eyes.”
Refraction: Test to determine the eye’s refractive power and the bending of light as it passes from one medium into another.
Refractive errors: The degree of visual distortion or limitation caused by inadequate bending of light rays, including hyperopia, myopia, and astigmatism.
Refractive power: The ability of an object, such as the eye, to bend light as light passes through it.
Refractive surgery: A type of surgery (such as LASIK) that affects vision refraction.
Retina: Layer of delicate sensory tissue that lines the inside wall of the eye, composed of light-sensitive cells known as rods and cones. It acts like a film in a camera to capture images, transform them into electrical signals, and send them to the brain through the optic nerve.
Retinal Detachment: Condition wherein the retina breaks away from the choroid membrane, causing it to lose nourishment and resulting in loss of vision unless successfully surgically repaired.
RK: Abbreviation for “radial keratotomy,” an outdated procedure once used to correct mild to moderate myopia, making a series of spoke-like incisions around its periphery flattens the cornea.
Rods: One of the two types of light-sensitive cells located primarily in the side areas of the retina (also see cones). About 125 million rods are responsible for visual sensitivity to movement, shapes, light, and dark (black and white), and the ability to see in dim light.
Routine eye exam: To test the overall condition of the eye and prescribe corrective measures such as glasses, contact lenses, or LASIK.
Schirmer test: A test for dry eyes that uses a thin strip of filter paper placed at the edge of the eye.
Sclera: White part of the eye. Tough covering that (with the cornea) forms the external, protective coat of the eye.
Scotoma: Area of partial or complete loss of vision surrounded by an area of normal vision, as can occur in advanced ARMD or glaucoma.
Single vision: Lenses with only one focal length.
Slit-Lamp: Ophthalmic instrument producing a slender beam of light used to illuminate and examine the external and internal parts of the eye.
Sloan eye chart: A standard chart that tests visual acuity with black letters of various sizes against a white background.
Snellen eye chart: The most common chart used to test visual acuity with black letters of various sizes against a white background.
Snellen lines: Snellen optotypes are arranged in horizontal rows, known as “lines.”
Snellen optotypes: Specifically formed letters of the alphabet arranged in rows of decreasing letter size on the Snellen chart.
Sphere: Focusing power of the corrective lens.
Stereoscopic vision: Ability to see in three dimensions.
Stereopsis: Ability to perceive three-dimensional depth.
Strabismus: A condition that occurs when the eye muscles do not align properly, and binocular vision is absent. Patients with a history of strabismus may develop double vision after refractive eye surgery.
Stroma: Middle, thickest layer of tissue in the cornea.
Suppression: Inability to perceive all or part of objects in the field of vision of one eye.
Suspensory ligament of lens: Series of fibers that connect the eye’s ciliary body with the lens, holding it in place; also known as zonules.
Sympathetic ophthalmia: Inflammation of one eye following inflammation in the other eye.
Tonometry: Procedure for the measurement of intraocular pressure. A glaucoma test.
Topography: A tool used to see the refractive problems that might be present in the cornea. Corneal topography is used not only for screening all patients before refractive surgery, such as LASIK, but also for fitting contact lenses.
Toric: Lens (eyeglasses, intraocular lens, or contact lens) that is warped (astigmatic) opposite to that of the eye, thereby canceling out the error.
Trabecular meshwork: Drainage channels located inside the eye.
Trabeculoplasty: A procedure for treating glaucoma using a laser (Argon or Nd:YAG). Trabeculoplasty remodels the trabecular meshwork to enhance aqueous drainage and reduce intraocular pressure.
Trifocals: Lenses containing three focal lengths, usually arranged with the focus for distance above, intermediate distance in the middle, and near vision below.
Twenty-twenty, 20/20 vision: Having 20/20 vision means that when you stand 20 feet away from the Snellen eye chart, you can see what most people can see at that same distance.
UCVA: Uncorrected visual acuity.
Uveal tract: Pigmented middle layers of the eye, which include the choroid, ciliary body, and iris.
Uveitis: Inflammation of any portion of the uveal tract.
Ultrasound waves: Sound waves with frequencies above 20,000 vibrations per second, which are beyond the range audible to the human ear, are used in medical diagnosis and surgery.
Ultrasonography: Recordings of the echoes of ultrasound waves sent into the eye and reflected from the structures inside the eye or orbit. Ultrasonography is used to make measurements and to detect and localize tumors and retinal detachments.
Ultraviolet radiation: Radiant energy with a wavelength just below that of visible light. UV-C is the shortest wavelength, ranging from 200 to 280 nm, and is absorbed by the atmosphere before reaching the surface. UV-b, at 280-315 nm, is the burning rays of the sun and damages most living tissue. UV-A, at 315-400 nm, is the sun’s tanning rays and can somewhat damage specific tissues. UV radiation has been identified as a contributing factor to particular eye disease processes, which can lead to ARMD and cataracts, and may also cause exposure to keratitis.
Uncorrected visual acuity (UCVA): The best possible vision a person can achieve without corrective lenses is measured using Snellen lines on an eye chart.
Undercorrection: Occurrence in refractive surgery where the achieved correction is less than desired; in LASIK, typically due to a patient under-responding to the laser treatment.
Vascular: Having to do with transporting blood.
Vision: The ability of the brain to see and interpret what is in front of the eyes.
Vision therapy: Orthoptics, vision training, eye exercises. The treatment process involves improving visual perception and/or coordination between the two eyes to achieve more efficient and comfortable binocular vision.
Visual acuity: Clearness of vision; the ability to distinguish details and shapes, which depends upon the sharpness of the retinal image.
Visual cortex: This part of the brain is responsible for vision.
Visual field: Area or extent of space visible to an eye in a given gaze position. There is a central visual field, the area directly in front of us, and a peripheral visual field, which encompasses our “side vision.” The fields of each eye partly overlap. We do not perceive the blind spots in each eye because the missing area in one eye is present in the other.
VISX CustomVue Procedure: WaveScan-driven laser vision correction has the potential to produce better vision than is possible with glasses or contact lenses, enabling surgeons to measure and correct unique imperfections in each individual’s vision.
VISX STAR S4 Excimer laser System: A highly advanced laser technology platform, the VISX STAR S4 combines Variable Spot Scanning (VSS), ActiveTrak 3-D Active Eye Tracking, and WavePrint.
Vitreous humor, fluid, or body: A jelly-like, colorless, transparent substance occupying the more significant part of the eye cavity and all the space between the crystalline lens and the retina.
Vitrectomy: Surgical removal of the vitreous humor that is diseased or has lost its transparency.
Wavefront: Wavefront technology produces a detailed map of the eye. The information is transferred to the laser via computer software.
YAG laser surgery: Properly called Nd:Yag laser capsulotomy, a procedure using an Nd:Yag (neodymium-yttrium-aluminum-garnet) laser, used primarily to treat secondary Cataracts (capsular haze) that occur after the primary cataract procedure, or to relieve increased pressure within the eye from acute angle-closure glaucoma via a peripheral iridotomy. It can also treat open-angle glaucoma in a procedure called selective laser trabeculoplasty.
