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20/20 20/20. Normal visual acuity. Upper number is the standard distance (20 ft.) between an eye being tested and the eye chart; lower number indicates that the tested eye can see the same small standard-sized letters or symbols as a normal eye at 20 feet.
Aberrometry Aberrometry A method of capturing the wavefront of an ocular system. Typically a light beam is projected into the eye and the aberrometer captures the existing rays as they are reflected off of the retina. The wavefront profile of the eye is then displayed in a two-dimensional or three-dimensional map. Usually five measurements are taken and the average of the three closest readings produces the final wavefront measurement. Wavefront maps are displayed in terms of Zernike polynomials and measured in microns.
Ablate Ablate In surgery, to remove.
accommodation Increase in optical power by the eye in order to maintain a clear image (focus) as objects are moved closer. Occurs through a process of ciliary muscle contraction and zonular relaxation that causes the elastic-like lens to "round up" and increase its optical power. Natural loss of accommodation with increasing age is called presbyopia.
after-cataract, secondary cataract after-cataract, secondary cataract. Remnants of an opaque lens remaining in the eye, or opacities forming, after extracapsular cataract removal.
age-related macular degeneration age-related macular degeneration. Group of conditions that include deterioration of the macula, resulting in loss of sharp central vision. Two general types: "dry," which is more common, and "wet," in which abnormal new blood vessels grow under the retina and leak fluid and blood (neovascularization), further disturbing macular function. Most common cause of decreased vision after age 60.
Age-Related Macular Degeneration (AMD) AMD is a condition that primarily affects the part of the retina responsible for sharp central vision. It does not cause total blindness. There are two forms of AMD — dry AMD and wet AMD. Because AMD often damages central vision, it is the most common cause of legal blindness and vision impairment in older Americans (AMD rarely affects those under the age of 60). While there is no generally accepted treatment for dry AMD, laser therapies or injectable medications can help destroy leaking blood vessels can help reduce the risk of advancing vision loss in many cases of wet AMD. Research sponsored by the National Eye Institute has recently shown that a combination of zinc, vitamins C and E, and beta-carotene may also reduce the risk of advanced AMD by 25 percent.
amblyopia "lazy eye." Decreased vision in one or both eyes without detectable anatomic damage to the retina or visual pathways. Usually uncorrectable by eyeglasses or contact lenses.
Amsler grid Amsler grid (AM-slur). Test card. Printed grid (black lines on white background or white lines on black background) used for detecting central visual field distortions or defects, such as in macular degeneration.
angle, anterior chamber angle angle, anterior chamber angle. Junction of the front surface of the iris and back surface of the cornea, where aqueous fluid filters out of the eye.
anterior chamber anterior chamber. Fluid-filled space inside the eye between the iris and the innermost corneal surface (endothelium).
aqueous aqueous (AY-kwee-us), aqueous humor. Clear, watery fluid that fills the space between the back surface of the cornea and the front surface of the vitreous, bathing the lens. Produced by the ciliary processes. Nourishes the cornea, iris, and lens and maintains intraocular pressure.
A-scan A-scan. Type of ultrasound; very high frequency sound waves that are reflected by the ocular structures and converted into electrical impulses. Used for measuring length of eyeball (axial length) prior to cataract surgery, to help determine power of IOL to be implanted; also to help differentiate normal and abnormal eye tissue.
Astigmatic Keratotomy Astigmatic Keratotomy (AK) Incisional surgical procedure used to correct corneal astigmatism. Arcuate incisions are placed in the corneal midperipheral zone of the steep meridian at approximately 90% depth.
astigmatism astigmatism (uh-STIG-muh-tiz-um). Refractive error. Optical defect in which refractive power is not uniform in all directions (meridians). Light rays entering the eye are bent unequally by different meridians, which prevents formation of a sharp image focus on the retina. Slight uncorrected astigmatism may not cause symptoms, but a large amount may result in significant blurring and headache.
Automated Lamellar Keratoplasty Automated Lamellar Keratoplasty (ALK) A refractive surgical procedure in which the surgeon creates a flap of the uppermost layer of the cornea using a microkeratome. A second pass of the microkeratome is made in order to remove a wedge of tissue.
Bifocals bifocals. Eyeglasses that incorporate two different powers in each lens, usually for near and distance corrections.
binocular vision binocular vision. Blending of the separate images seen by each eye into one composite image.
blepharitis blepharitis (blef-uh-RI-tus). Inflammation of the eyelids, usually with redness, swelling, and itching.
blind spot blind spot. Sightless area within the visual field of a normal eye. Caused by absence of light sensitive photoreceptors where the optic nerve enters the eye.
Broad Beam Laser Broad Beam Laser Excimer laser where the beam size used to ablate the cornea is from approximately 6.0 to 8.0 millimeters.
B-scan B-scan. Type of ultrasound; provides a cross-section view of tissues that cannot be seen directly. High frequency sound waves are reflected by eye tissues and orbital structures and converted into electrical pulses, which are displayed on a printout.
Cataract Cataract is a clouding of the eye’s naturally clear lens. Most cataracts appear with advancing age. The most important factor in cataract formation is increasing age, but there are additional factors, including smoking, diabetes, and excessive exposure to sunlight. Cataract is the leading cause of blindness in the world, and affects nearly 20.5 million Americans age 40 and older. By age 80, more than half of all Americans develop cataract. Cataract is sometimes considered a conquered disease because surgical treatment that can eliminate vision loss due to the disease is widely available. The cataract is removed surgically and a plastic lens, called an implant, is placed in the eye restoring normal sight.
cataract cataract. Opacity or cloudiness of the crystalline lens, which may prevent a clear image from forming on the retina. Surgical removal of the lens may be necessary if visual loss becomes significant, with lost optical power replaced with an intraocular lens, contact lens, or aphakic spectacles. May be congenital or caused by trauma, disease, or age.
cataract extraction cataract extraction. Removal of a cloudy lens from the eye. An extracapsular cataract extraction leaves the rear lens capsule intact; with an intracapsular extraction there is complete removal of lens with its capsule, usually by cryoextraction.
central retinal artery central retinal artery. First branch of the ophthalmic artery; supplies nutrition to the inner two-thirds of the retina.
central retinal artery central retinal artery. First branch of the ophthalmic artery; supplies nutrition to the inner two-thirds of the retina.
central retinal vein central retinal vein. Blood vessel that collects retinal venous blood drainage; exits the eye through the optic nerve
central vision central vision. An eye's best vision; used for reading and discriminating fine detail and color. Results from stimulation of the fovea and the macular area.
chalazion chalazion (kuh-LAY-zee-un). Inflamed lump in a meibomian gland (in the eyelid). Inflammation usually subsides, but may need surgical removal. Sometimes called an internal hordeolum.
Choroid choroid (KOR-oyd). Vascular (major blood vessel) layer of the eye lying between the retina and the sclera. Provides nourishment to outer layers of the retina.
color blindness color blindness. Reduced ability to discriminate between colors, especially shades of red and green. Usually hereditary.
Conductive Keratoplasty Conductive Keratoplasty (CK) CK is a non-ablative, collagen-shrinking procedure for the treatment of mild and moderate hyperopia. Radiofrequency energy is delivered through a fine tip inserted into the corneal stroma. The collagen lamellae in the area surrounding the tip shrink and tighten, increasing the radius of curvature of the cornea. The spots are placed in the circumference of the mid- and peripheral cornea. Based on the amount of refractive change targeted, the number and location of treatment spots may be determined, with larger treatments requiring more spots and rings.
cone cone. Light-sensitive retinal receptor cell that provides sharp visual acuity and color discrimination.
conjunctiva conjunctiva (kahn-junk-TI-vuh). Transparent mucous membrane covering the outer surface of the eyeball except the cornea, and lining the inner surfaces of the eyelids.
conjunctivitis conjunctivitis (kun-junk-tih-VI-tis), "pink eye. " Inflammation of the conjunctiva. Characterized by discharge, grittiness, redness and swelling. Usually viral in origin, but may be bacterial or allergic; may be contagious.
Conventional Refractive Surgery Conventional Refractive Surgery Method of optical correction by Excimer laser photoablation, which changes the shape of the cornea to change the refraction error. The treatments are symmetrical and correct lower order or spherocylindrical aberrations, which include myopia, hyperopia, and astigmatism.
convergence convergence. Inward movement of both eyes toward each other, usually in an effort to maintain single binocular vision as an object approaches.
cornea cornea (KOR-nee-uh). Transparent front part of the eye that covers the iris, pupil, and anterior chamber and provides most of an eye's optical power.
Customized Refractive Surgery Customized Refractive Surgery Wavefront-driven excimer laser photoablation, which changes the shape of the cornea to change refractive error. In addition to treating lower-order aberrations (sphere and cylinder), custom refractive surgery treats higher-order aberrations up to the 6th order. Wavefront-guided ablations create treatment profiles based on wavefront maps and the treatment may be asymmetrical and is customized for the individual patient. The treatment parameters vary according to the system utilized. The first customized laser platform was FDA approved in the fall of 2002.
cycloplegic refraction cycloplegic refraction. Assessment of an eye's refractive error after lens accommodation has been paralyzed with cycloplegic eyedrops (to eliminate variability in optical power caused by a contracting lens). Series of lenses in graded powers are presented to determine which provide the sharpest, clearest vision.
Diabetic Retinopathy Diabetic Retinopathy is a common complication of diabetes. Retinal blood vessels can break down, leak, or become blocked, affecting and impairing vision over time. Nearly half of all people with diabetes will develop some degree of diabetic retinopathy during their lifetime, and risk increases with age and duration of diabetes. People with diabetes are encouraged to seek annual dilated eye exams. Currently, laser surgery and a procedure called a vitrectomy are highly effective in treating diabetic retinopathy.
diabetic retinopathy diabetic retinopathy (ret-in-AHP-uh-thee). Spectrum of retinal changes accompanying long-standing diabetes mellitus. Early stage is background retinopathy. May advance to proliferative retinopathy, which includes the growth of abnormal new blood vessels (neovascularization) and fibrous tissue.
dilated pupil dilated pupil. Enlarged pupil, resulting from contraction of the dilator muscle or relaxation of the iris sphincter. Occurs normally in dim illumination, or may be produced by certain drugs (mydriatics, cycloplegics) or result from blunt trauma.
diopter diopter (D) (di-AHP-tur). Unit to designate the refractive power of a lens.
diplopia, double vision diplopia, double vision. Perception of two images from one object; images may be horizontal, vertical or diagonal.
drusen drusen (DRU-zin). Tiny, white hyaline deposits on Bruch's membrane (of the retinal pigment epithelium). Common after age 60; sometimes an early sign of macular degeneration.
dry eye syndrome dry eye syndrome. Corneal and conjunctival dryness due to deficient tear production, predominantly in menopausal and post-menopausal women. Can cause foreign body sensation, burning eyes, filamentary keratitis, and erosion of conjunctival and corneal epithelium.
Ectasia Ectasia Progressive corneal thinning and associated protrusion.
ectropion ectropion (ek-TROH-pee-un). Outward turning of the upper or lower eyelid so that the lid margin does not rest against the eyeball, but falls or is pulled away. Can create corneal exposure with excessive drying, tearing, and irritation. Usually from aging.
emmetropia emmetropia (em-uh-TROH-pee-uh). Refractive state of having no refractive error when accommodation is at rest. Images of distant objects are focused sharply on the retina without the need for either accommodation or corrective lenses.
entropion entropion (en-TROH-pee-un). Inward turning of upper or lower eyelid so that the lid margin rests against and rubs the eyeball.
Epi-LASIK Epi-LASIK Refractive surgical procedure. This new procedure is believed to avoid risks associated with laser-assisted in situ keratomileusis (LASIK) and offers improved postoperative recovery compared with Photorefractive Keratectomy (PRK). Rather than creating a flap with a microkeratome as in LASIK or removing the epithelium as in PRK, Epi-LASIK separates an epithelial sheet using the Centurion SES EpiEdge epikeratome (CIBA Vision).
Epithelial Ingrowth Epithelial Ingrowth A LASIK complication wherein epithelial cells proliferate underneath the corneal flap.
esotropia esotropia (ee-soh-TROH-pee-uh), cross-eyes. Eye misalignment in which one eye deviates inward (toward nose) while the other fixates normally.
excimer laser excimer laser (EKS-ih-mur). Class of ultraviolet lasers that removes tissue accurately without heating it. In refractive corneal surgery, controlled by computer to make precise pre-programmed shavings of eye tissue to produce a given optical correction.
Excimer Laser Excimer Laser Type of laser used in all laser refractive surgical procedures in order to reduce refractive error. The laser utilizes a 193 nm argon-fluoride beam to reshape the anterior corneal stroma by breaking collagen bonds and expelling or ablating corneal tissue with each laser pulse. It is termed a “cold” laser because the collagen bonds are broken without damaging adjacent cells. The pulses are fired centrally to flatten the cornea to an oblate shape in myopia and fired peripherally to steepen the cornea to a prolate shape in hyperopia.
exotropia exotropia (eks-oh-TROH-pee-uh), wall-eyes. Eye misalignment in which one eye deviates outward (away from nose) while the other fixates normally.
extraocular muscles extraocular muscles (eks-truh-AHK-yu-lur). Six muscles that move the eyeball (lateral rectus, medial rectus, superior oblique, inferior oblique, superior rectus, inferior rectus).
eyelids eyelids. Structures covering the front of the eye, which protect it, limit the amount of light entering the pupil, and distribute tear film over the exposed corneal surface.
Femtosecond Laser Femtosecond Laser High-frequency laser now used to make flaps in the LASIK procedure. The high-frequency energy can be focused through the anterior cornea to a specified depth. A sweeping back and forth (raster) pattern creates a horizontal, then vertical cleavage plane to create the flap.
floaters floaters. Particles that float in the vitreous and cast shadows on the retina; seen as spots, cobwebs, spiders, etc. Occurs normally with aging or with vitreous detachment, retinal tears, or inflammation.
fluorescein angiography fluorescein angiography (FLOR-uh-seen an-jee-AH-gruh-fee).Technique used for visualizing and recording location and size of blood vessels and any eye problems affecting them; fluorescein dye is injected into an arm vein, then rapid, sequential photographs are taken of the eye as the dye circulates.
fovea fovea (FOH-vee-uh). Central pit in the macula that produces sharpest vision. Contains a high concentration of cones and no retinal blood vessels.
Glaucoma Glaucoma is a disease that causes gradual damage to the optic nerve that carries visual information from the eye to the brain. The loss of vision is not experienced until a significant amount of nerve damage has occurred. For this reason, as many as half of all people with glaucoma are unaware of their disease. About 2.2 million Americans age 40 and older have been diagnosed with glaucoma, and another two million do not know they have it. Most cases of glaucoma can be controlled by medication or surgery and vision loss slowed or halted by timely diagnosis and treatment. However, any vision lost to glaucoma cannot be restored.
glaucoma glaucoma (glaw-KOH-muh). Group of diseases characterized by increased intraocular pressure resulting in damage to the optic nerve and retinal nerve fibers. A common cause of preventable vision loss. May be treated by prescription drugs or surgery.
gonioscopy gonioscopy (goh-nee-AHS-koh-pee). Examination of the anterior chamber angle through a goniolens (special type of contact lens).
hyperopia hyperopia (hi-pur-OH-pee-uh), farsightedness. Refractive error. Focusing defect in which an eye is underpowered; light rays coming from a distant object strike the retina before coming to sharp focus, blurring vision. Farsighted people expend focusing effort to see clearly in the distance, and close-up vision is blurred because it takes even more focusing effort. Corrected with additional optical power, which may be supplied by a plus lens (spectacle or contact) or by excessive use of the eye's own focusing ability (accommodation).
hyphema hyphema (hi-FEE-muh). Blood in the anterior chamber, such as following blunt trauma to the eyeball.
intraocular pressure intraocular pressure. 1. Fluid pressure inside the eye. 2. The assessment of pressure inside the eye with a tonometer. Also called tension.
Intrastromal Corneal Ring Segments (ICRS) Intrastromal Corneal Ring Segments (ICRS) A reversible procedure used in the treatment of low amounts of myopia (-1.00 to -3.00 D) by placing rings of polymethylmethacrylate (PMMA) in the midperipheral corneal stroma to flatten the radius of curvature. Intrastromal corneal ring segments are currently being investigated to reduce myopia in patients with keratoconus and corneal ectasia.
IOL (intraocular lens) IOL (intraocular lens). Plastic lens that may be surgically implanted to replace the eye's natural lens.
iris iris. Pigmented tissue lying behind the cornea that gives color to the eye (e.g., blue eyes) and controls amount of light entering the eye by varying the size of the pupillary opening.
keratoconus keratoconus (kehr-uh-toh-KOH-nus). Degenerative corneal disease affecting vision. Characterized by generalized thinning and cone-shaped protrusion of the central cornea, usually in both eyes. Hereditary.
Keratomileusis Keratomileusis The sculpting of the cornea, formerly done with a lathe and blade, now done with an excimer laser.
Keratoplasty Keratoplasty The replacement of the cornea. Keratoplasty can be lamellar (replacement of the superficial layers) or penetrating (transplantation or replacement of the full thickness of the cornea).
Keratotomy Keratotomy A surgical incision of the cornea.
lacrimal gland lacrimal gland. Almond-shaped structure that produces tears. Located at the upper outer region of the orbit, above the eyeball.
laser laser. Acronym: Light Amplification by Stimulated Emission of Radiation. High energy light source that uses light emitted by the natural vibrations of atoms (of a gas or solid material) to cut, burn or dissolve tissues for various clinical purposes: in the retina, to treat diabetic retinopathy and macular degeneration, to destroy leaking and new blood vessels (neovascularization); on the iris or trabecular meshwork, to decrease pressure in glaucoma; after extracapsular cataract extraction, to open the posterior lens capsule.
LASER LASER An acronym for light amplification by stimulated emission of radiation.
Laser Epithelial Keratomileusis (LASEK) Laser Epithelial Keratomileusis (LASEK)
A hybrid of photorefractive keratectomy (PRK) and laser-assisted in situ keratomileusis (LASIK), the goal of LASEK is the preservation of the corneal epithelium. Rather than creating a flap with a microkeratome (as in LASIK) or scraping and removing the patient’s epithelium (as in PRK), LASEK treats the epithelium with alcohol to loosen and separate it from the stroma and it is then rolled back. The underlying stroma is ablated with an excimer laser and the epithelial cells are rolled back out, repositioned, and smoothed. The potential advantages of LASEK are to reduce postoperative haze, speed visual recovery, and decrease postoperative pain over traditional PRK.
Laser Thermal Keratoplasty (LTK) Laser Thermal Keratoplasty (LTK) Approved by the FDA in 2000 for the temporary correction of hyperopia ranging from +0.75 to +2.50 D with less than 1.0 D of astigmatism. LTK uses a Holmium:YAG laser comprised of a slit-lamp delivery system that creates spots around the circumference of the peripheral cornea. The treatment consists of either one or two rings of spots set at an optical zone of 6.0 and/or 7.0 mm.
Laser-Assisted In Situ Keratomileusis (LASIK) Laser-Assisted In Situ Keratomileusis (LASIK) Approved by the FDA for the correction of myopia, hyperopia and astigmatism. LASIK is a combination of two refractive technologies: Use of a microkeratome, to create a thin flap of tissue (approximately 130 to 180 microns thick) followed by excimer laser ablation to reshape the stromal tissue beneath the flap.
LASIK LASIK (LAY-sik). Acronym: LAser in SItu Keratomileusis. Type of refractive surgery in which the cornea is reshaped to change its optical power. A disc of cornea is raised as a flap, then an excimer laser is used to reshape the intrastromal bed, producing surgical flattening of the cornea. Used for correcting myopia, hyperopia, and astigmatism.
Legal Blindness Legal Blindness in the United States, where normal vision is considered to be 20/20, legal blindness is defined as visual acuity with best correction in the better eye worse than or equal to 20/200 or a visual field extent of less than 20 degrees in diameter. Most states use these standards to provide rehabilitation services and benefits to people who are visually impaired. Some of these benefits and services include an IRS income tax exemption, free telephone directory assistance, free Talking Book Library Services through the National Library Service and Vocational and Independent Living Services through individual state programs. Please note the term Legal Blindness does not mean that a legally blind person is blind or has no usable vision. Most people defined as legally blind have usable vision and can perform most daily tasks with the use of special glasses or low vision aids.
lens, crystalline lens. lens, crystalline lens. The eye's natural lens. Transparent, biconvex intraocular tissue that helps bring rays of light to a focus on the retina.
Low Vision Low Vision is a visual impairment that cannot be corrected by standard eyeglasses, contact lenses, medication, or surgery, that interferes with the ability to perform everyday activities. Macular degeneration, diabetic retinopathy, glaucoma, and retinitis pigmentosa, along with many other eye diseases, are causes of visual impairment or low vision. Most people begin to experience difficulty with daily activities such as reading when their vision reaches 20/60 or worse and should seek out the care of a low vision specialist.
Low Vision Aids Low Vision Aids are Prescription and nonprescription devices that help people with low vision enhance their remaining vision. Some examples include special low vision eye glasses, telescopic lenses for driving and other distance tasks, microscopic reading glasses, magnifiers, CCTV’s (Electronic Reading Machines), large print books, check-writing guides and white canes. All optical low vision aids, including eyeglasses, magnifiers and telescopes, should be prescribed by either an optometrist or ophthalmologist to ensure the correct power and success of the patient.
macula macula. Small central area of the retina surrounding the fovea; area of acute central vision.
Microkeratome Microkeratome Instrument used for the creation of a lamellar flap (130 to 180 mm) during laser-assisted in situ keratomileusis (LASIK). A microkeratome is comprised of a suction ring that adheres to the globe, providing stability for the cutting blade that rolls along a tongue and groove track, creating the flap.
Micron Micron One thousandth of a millimeter. One millionth of a meter.
myopia myopia (mi-OH-pee-uh), nearsightedness. Focusing defect in which the eye is overpowered. Light rays coming from a distant object are brought to focus before reaching the retina. Requires a minus lens correction to "weaken" the eye optically and permit clear distance vision.
neovascularization neovascularization (nee-oh-VAS-kyu-lur-ih-ZAY-shun). Abnormal formation of new blood vessels, usually in or under the retina or on the iris surface. May develop in diabetic retinopathy, blockage of the central retinal vein, or macular degeneration.
Nomogram Nomogram The surgical adjustment to a laser’s computer calculation to further refine results.
nystagmus nystagmus (ni-STAG-mus). Involuntary, rhythmic side-to-side or up and down (oscillating) eye movements that are faster in one direction than the other.
Occupational Therapist Occupational Therapist — Occupational therapists are skilled professionals who help individuals achieve independence. They can provide treatment only with the prescription of a medical doctor or a doctor of optometry. Occupational therapists who specialize in low vision rehabilitation train their clients to use optical and non-optical devices, adaptive techniques and educate in community resources.
Ophthalmologist Ophthalmologist — An ophthalmologist is a medical doctor who specializes in eye and vision care. Eye M.D.’s are specially trained to provide the full spectrum of eye care, from prescribing glasses and contact lenses to complex and delicate eye surgery.
optic disc, optic nerve head optic disc, optic nerve head. Ocular end of the optic nerve. Denotes the exit of retinal nerve fibers from the eye and entrance of blood vessels to the eye.
optic nerve optic nerve. Largest sensory nerve of the eye; carries impulses for sight from the retina to the brain.
Optician Optician — A trained professional who grinds, fits, and dispenses glasses by prescription from an optometrist or ophthalmologist.
Optometrist Optometrist are Doctors of optometry (ODs) are primary health care professionals for the eye. Optometrists examine, diagnose, treat, and manage diseases, injuries, and disorders of the eye. They prescribe glasses, contact lenses and low vision aids.
Orientation and Mobility Specialist Orientation and Mobility Specialist — A person who trains people with low vision to move about safely in the home and travel by themselves.
orthoptics orthoptics. Discipline dealing with the diagnosis and treatment of defective eye coordination, binocular vision, and functional amblyopia by non-medical and non-surgical methods, e.g., glasses, prisms, exercises.
Pachymetry Pachymetry Measurement of corneal thickness. Methods of measurement are based on wave reflection of optical light or ultrasonic energy through the corneal tissue.
patching patching. Covering an amblyopic patient's preferred eye, to improve vision in the other eye.
perimetry perimetry (puh-RIM-ih-tree). Test. Method of charting extent of a stationary eye's field of vision with test objects of various sizes and light intensities. Aids in detection of damage to sensory visual pathways.
peripheral vision peripheral vision. Side vision; vision elicited by stimuli falling on retinal areas distant from the macula.
phacoemulsification phacoemulsification (fay-koh-ee-mul-sih-fih-KAY-shun). Surgical procedure. Use of ultrasonic vibration to shatter and break up a cataract, making it easier to remove.
photophobia photophobia (foh-toh-FOH-bee-uh). Abnormal sensitivity to, and discomfort from, light. May be associated with excessive tearing. Often due to inflammation of the iris or cornea.
Photorefractive Keratectomy Photorefractive Keratectomy (PRK) A procedure involving the removal of the epithelium by gentle scraping away of the corneal epithelium and use of a computer-controlled excimer laser to reshape the stroma.
Phototherapeutic Keratotomy (PTK) Phototherapeutic Keratotomy (PTK) PTK involves ablative photodecomposition of the epithelium by ablating microscopically thin layers and etching away surface irregularities. Candidates for PTK are patients with significant visual compromise due to corneal scars and opacities (from trauma or inactive infections), dystrophies (Reis-Buckler’s, lattice, anterior basement membrane dystrophy [ABMD]), irregular corneal surface associated with filamentary keratitis and Salzmann’s nodular degeneration, recurrent corneal erosions (RCE) (unresponsive to lubricants, debridement, or stromal puncture), band keratopathy, scars resulting from previous pterygium excision, Thygeson’s superficial keratitis, and irregular astigmatism.
pinguecula pinguecula (pin-GWEK-yu-luh). Yellowish-brown subconjunctival elevation composed of degenerated elastic tissue; may occur on either side of the cornea. Benign.
presbyopia presbyopia (prez-bee-OH-pee-uh). Refractive condition in which there is a diminished power of accommodation arising from loss of elasticity of the crystalline lens, as occurs with aging. Usually becomes significant after age 45.
PRK (photorefractive keratectomy) PRK (photorefractive keratectomy). Use of high intensity laser light (e.g., an excimer laser) to reshape the corneal curvature; for correcting refractive errors.
progressive addition lens (PAL) progressive addition lens (PAL), progressive-power lens.. Eyeglass lens that incorporates corrections for distance vision, through midrange, to near vision (usually in lower part of lens), with smooth transitions and no bifocal demarcation line.
pterygium (tur-IH-jee-um) pterygium (tur-IH-jee-um). Wedge-shaped growth on the bulbar conjunctiva. May gradually advance onto the cornea and require surgical removal. Probably related to sun irritation.
ptosis ptosis (TOH-sis). Drooping of upper eyelid. May be congenital or caused by paralysis or weakness of the 3rd cranial nerve or sympathetic nerves, or by excessive weight of the upper lids.
pupil pupil. Variable-sized black circular opening in the center of the iris that regulates the amount of light that enters the eye.
radial keratotomy radial keratotomy (RK) (keh-ruh-TAH-tuh-mee). Surgical procedure. Series of spoke-like (radial) cuts made in the corneal periphery to allow the central cornea to flatten, reducing its optical power and thereby correcting nearsightedness.
Radial Keratotomy Radial Keratotomy (RK) Refractive surgical procedure popular in the 1980s, RK treated low amounts of myopia ranging from -1.00 to -4.00 D. In order to flatten the cornea, radial incisions (like the spokes of a wheel) were created using a diamond-blade micrometer knife, leaving a central unaltered optical zone of approximately 3.0 mm.
refraction refraction. Test to determine an eye's refractive error and the best corrective lenses to be prescribed. Series of lenses in graded powers are presented to determine which provide sharpest, clearest vision.
refractive error refractive error. Optical defect in an unaccommodating eye; parallel light rays are not brought to a sharp focus precisely on the retina, producing a blurred retinal image. Can be corrected by eyeglasses, contact lenses, or refractive surgery.
Refractive Surgery Refractive Surgery A surgical method of vision correction by changing the refractive properties of the eye.
retina retina (RET-ih-nuh). Light sensitive nerve tissue in the eye that converts images from the eye's optical system into electrical impulses that are sent along the optic nerve to the brain, to interpret as vision. Forms a thin membranous lining of the rear two-thirds of the globe.
retinal detachment retinal detachment. Separation of the retina from the underlying pigment epithelium. Disrupts visual cell structure and thus markedly disturbs vision. Almost always caused by a retinal tear; often requires immediate surgical repair.
rod rod. Light-sensitive, specialized retinal receptor cell that works at low light levels (night vision). A normal retina contains 150 million rods.
Schlemm's canal Schlemm's canal (shlemz). Circular channel deep in corneoscleral junction (limbus) that carries aqueous fluid from the anterior chamber of the eye to the bloodstream.
sclera sclera (SKLEH-ruh). Opaque, fibrous, protective outer layer of the eye ("white of the eye") that is directly continuous with the cornea in front and with the sheath covering optic nerve behind.
Scleral Expansion Bands Scleral Expansion Bands (SEB) Procedure potential is for the reversal of presbyopia. Increasing lens zonular tension by implanting small polymethylmethacrylate (PMMA) bands in the sclera over the ciliary body will allow accommodation to occur.
slit lamp slit lamp. Microscope used for examining the eye; allows cornea, lens and otherwise clear fluids and membranes to be seen in layer-by-layer detail.
Snellen chart Snellen chart. Test chart used for assessing visual acuity. Contains rows of letters, numbers, or symbols in standardized graded sizes, with a designated distance at which each row should be legible to a normal eye. Usually tested at 20 ft.
Specialist in Low Vision Rehabilitation Specialist in Low Vision Rehabilitation — An optometrist or ophthalmologist who specializes in the evaluation and management of low vision rehabilitation. These doctors help their patients enhance their remaining vision with special low vision eyeglasses and microscopic and telescopic low vision aids. The doctors will also prescribe other optical and nonoptical low visions aids as well as appropriate low vision services. They help their patients perform their daily activities despite a visual impairment so that they can enjoy life and remain independent. A doctor who specializes in low vision rehabilitation does not take the place of your current optometrist or ophthalmologist. They will work in conjunction with your eye doctor to maximize your remaining vision.
strabismus strabismus (struh-BIZ-mus). Eye misalignment caused by extraocular muscle imbalance: one fovea is not directed at the same object as the other.
sty, stye sty, stye. Acute pustular infection of the oil glands of Zeis, located in an eyelash follicle at the eyelid margin.
trabecular meshwork trabecular meshwork (truh-BEK-yu-lur). Mesh-like structure inside the eye at the iris-scleral junction of the anterior chamber angle. Filters aqueous fluid and controls its flow into the canal of Schlemm, prior to its leaving the anterior chamber.
trifocal trifocal (TRI-foh-kul). Eyeglass lens that incorporates three lenses of different powers. The main portion is usually focused for distance (20 ft.), the center segment for about 2 ft., and the lower segment for near (14 in.).
uvea, uveal tract uvea, uveal tract (YU-vee-uh). Pigmented layers of the eye (iris, ciliary body, choroid) that contain most of the intraocular blood vessels.
Vision Rehabilitation Teacher Vision Rehabilitation Teacher — A person who trains people with low vision to use optical and non-optical devices, adaptive techniques, and community resources.
visual acuity visual acuity. Assessment of the eye's ability to distinguish object details and shape, using the smallest identifiable object that can be seen at a specified distance (usually 20 ft. or 16 in.).
visual field visual field. Full extent of the area visible to an eye that is fixating straight ahead.
vitreous vitreous (VlT-ree-us), vitreous humor. Transparent, colorless gelatinous mass that fills the rear two-thirds of the eyeball, between the lens and the retina.
vitreous detachment vitreous detachment. Separation of vitreous gel from retinal surface. Usually innocuous, but can cause retinal tears, which may lead to retinal detachment. Frequently occurs with aging as the vitreous liquifies, or in some disease states, e.g. diabetes and high myopia.
Wavefronts Wavefronts Wavefront capture by an aberrometer is the measurement of lower- and higher-order aberrations. As a wavefront passes through multiple refractive surfaces, ocular aberrations are induced that prevent individual light beams from focusing at the same point on the macula. Ocular aberrations increase as a function of pupil size and become visually significant with pupil dilation. In a perfect optical system the wavefront would be flat. Optical aberrations are as unique as a person’s fingerprint, with each eye producing its own unique wavefront . Once a patient’s wavefront is captured, it is incorporated into the refractive surgical procedure for a customized treatment.
YAG laser. YAG laser. Laser that produces short pulsed, high energy light beam to cut, perforate, or fragment tissue.