Ординатура / Офтальмология / Английские материалы / The Encyclopedia of Blindness and Vision Impairment_Sardegna, Shelly, Shelly, Steidl_2002

lifornia, Arizona, Nevada, Guam, Saipan, and American Samoa.

¥Conducts engineering research through projects such as the Universal Access System, which provides access to any computer through a laptop computer.

¥Hosts a monthly radio show on KIEV (Los Angeles) on the subject of Technology and Persons with Disabilities.

Other CSUN-sponsored conferences include those concerning learning disabilities, art for disabled persons, and employment-related topics.

Students entering universities or colleges may receive funding for personal readers or educational materials from the state agency for the blind. Federal transition services offered through state commissions for the blind or vocational-rehabilitation agencies are a federal priority but are not mandated.

Contact:

CSUN Center on Disabilities 1811 Nordhoff Street Northridge, CA 91330-8340 818-677-2578 (voice and TTY) 818-677-4929 (fax) www.csun.edu/cod

Urban Mass Transportation Act (UMTA) As amended in 1970, the Urban Mass Transportation Act of 1964 (UMTA) requires that mass transportation facilities and services be designed to accommodate use by elderly and disabled persons. A program of grants and loans was authorized in the act to fund such facilities and services.

The act established three programs:

1.The Mass Transportation Technology Research and Demonstration Program funds projects of national priority, including accessibility to mass transportation by elderly and disabled persons.

2.The Urban Mass Transportation Technical Studies Program funds grants for planning, engineering, and designing mass-transportation projects, including those specially designed with accommodation for elderly and disabled passengers in mind.

3.The Urban Mass Transportation Demonstration Grants Program funds demonstration projects that improve accessibility using innovative methods.

The National Mass Transportation Assistance Act of 1974 amended the Urban Mass Transportation formula-grant program by requiring project applicants to set fares for elderly and disabled passengers traveling at nonpeak hours at one-half the normal peak-hour fare price. The amendment allowed local transportation systems that transport elderly and disabled persons for free to remain eligible for federal formula-grant aid.

The Surface Transportation and Uniform Relocation Assistance Act of 1987 required the Secretary of Transportation to conduct a feasibility study for standards development for UMTA-funded programs concerning tactile aids to improve accessibility to blind and visually impaired passengers.

The Omnibus Budget Reconciliation Act of 1987 founded a three-year demonstration project operated by the Easter Seal Society to improve accessibility to transportation for disabled persons. The program uses UMTA funds to develop methods for identifying disabled persons within the community and training programs for transit operators and disabled persons.

The Intermodal Surface Transportation Efficiency Act of 1991, signed into law by President George H. W. Bush, allocated funds for public ground transportation, provided it complied with the Americans with Disabilities Act.

U.S. Department of Education. Summary of Existing Legislation Affecting Persons with Disabilities. Washington, D.C.: USDE, 1988.

Usher’s syndrome An inherited condition combining a serious hearing loss and a progressive loss of vision caused by RETINITIS PIGMENTOSA (RP). According to the RP FOUNDATION FIGHTING BLIND-

NESS, there are between 10,000 and 15,000 people with UsherÕs syndrome in the United States. It is the major cause of deaf-blindness.

There are three known types of UsherÕs syndrome. Type I individuals are born with a profound hearing loss and retinitis pigmentosa. Individuals

with Type II are born with a mild to moderate hearing loss and generally have a less severe form of RP. Type III UsherÕs syndrome is characterized by hearing loss and vision loss due to RP that are both progressive.

Retinitis pigmentosa is characterized by a degeneration of the RODS AND CONES (light-sensitive cells) of the RETINA. The retina of the eye receives the reßected light from an object, and the rods and cones translate the light into electrical impulses that the retina sends to the brain through the OPTIC NERVE. The brain changes the impulses into an image.

The rods function in low light or darkness and are responsible for detecting movement and shape. They are scattered throughout the retina and are accountable for peripheral or side vision. The cones discern detail and color and require light to work effectively. They are concentrated into the central section of the retina, the MACULA, and are responsible for central vision.

Retinitis pigmentosa attacks the rods Þrst, then the cones. As the disease progresses, night vision diminishes and peripheral or side vision is lost. Over long periods of time, central vision is affected. The vision loss may not be apparent for several years. Tunnel vision and night blindness may become noticeable during adolescence, and progressively worsen.

Roughly 30 percent of those with retinitis pigmentosa report a hearing loss, some of whom may be considered to have UsherÕs syndrome. UsherÕs syndrome accounts for up to 3 percent of all cases of profound deafness. The hearing loss is caused by a malfunction in the sensory cells of the inner ear by an unknown cause. The loss is generally present at birth or follows shortly after birth.

UsherÕs syndrome can be diagnosed. The hearing loss is easily detected with audiometric testing. RP can be diagnosed by the characteristic changes that take place in the retina. Tests such as an electroretinogram and a visual-Þeld test may be performed to conÞrm the diagnosis.

UsherÕs syndrome affects individuals of all races, ethnic and cultural backgrounds and is equally prevalent among males and females. It is a recessively inherited disorder that requires the necessary gene from both the mother and father. A

pairing of two carriers of the gene results in a one in four chance of producing UsherÕs syndrome. A pairing of a carrier and a noncarrier of the gene seldom results in UsherÕs syndrome, but the gene is passed on to future generations. At present, there is no method for determining a gene carrier other than tracing family history of the disease. Genetic counseling may be beneÞcial in prevention of the disease.

Scientists have made signiÞcant progress in the late 1990s to learn more about the defects that cause UsherÕs syndrome. Researchers think there are nine different genes that contain mutations that cause various types of UsherÕs syndrome. They are currently working to develop rodent models of UsherÕs syndrome that will help them understand how the genes function and how mutations in the gene lead to the hearing and vision loss that is typical of the disease.

There is no cure for UsherÕs syndrome or retinitis pigmentosa although a speciÞed amount of vitamin A has been found to slow the progression of RP in some people. The hearing loss tends to remain stable, but since it is an inner ear loss, surgery is not possible to restore hearing. Some individuals without any residual hearing have been candidates for cochlear implants. Many of those with residual hearing have beneÞted from hearing aids.

The progressive sight loss is untreatable. Each case is unique and unpredictable. The retina may degenerate rapidly or over a period of decades. Usually, some central vision is maintained through middle age. Most UsherÕs syndrome patients who become legally blind retain some central vision.

Cataracts, a clouding of the eyeÕs lens, may develop in patients with RP and UsherÕs syndrome. If the CATARACT is removable, the surgery does not improve retinal degeneration but can restore the visual acuity lost to the opacity of the cataract.

In the research for a cure or treatment for UsherÕs syndrome and retinitis pigmentosa, experiments and studies involving DMSO applications and light deprivation have had less than satisfactory results. UsherÕs syndrome patients may maximize their residual vision with low-vision aids. Optical aids such as Corning or NOIR glasses,

telescopes, microscopes, and night-vision aids may be useful. Nonoptical and electronic aids such as the Wide Angle Mobility Light, large print, talking computers, and closed-circuit television may further independence. However, these low-vision aids cannot restore vision that has been lost to RP or UsherÕs syndrome.

Annala, L. ÒFacing the Future with UsherÕs Syndrome.Ó Workshop on UsherÕs syndrome (December 2Ð3, 1976). Helen Keller National Center, Sands Point, NY.

Boardman, L. ÒMy Son has UsherÕs Syndrome.Ó The DeafBlind American. (June 1985): pp. 50Ð60.

The Foundation Fighting Blindness. Usher Syndrome Gene Identified. Hunt Valley, Md.: The Foundation for Fighting Blindness, 2001.

Pimentel, A. ÒHandling the Upper, Secondary and College UsherÕs Syndrome Student.Ó Workshop on UsherÕs syndrome (December 2Ð3, 1976). Helen Keller National Center, Sands Point, NY.

Roehrig, A. ÒLiving with UsherÕs Syndrome.Ó Workshop on UsherÕs syndrome (December 2Ð3, 1976). Helen Keller National Center, Sands Point, NY.

RP Foundation Fighting Blindness. Answers to Your Questions about Usher’s Syndrome. Baltimore, Maryland: RPFFB, 1988.

Vernon, McCay, Joann A. Boughman and Linda Annala. ÒConsiderations in Diagnosing UsherÕs Syndrome: RP and Hearing Loss.Ó Journal of Visual Impairment and Blindness, 76 (1982): 258Ð261.

uvea The uvea, or uveal tract, is a heavily vascularized layer that supplies blood to the eye. It includes the melanin-pigmented portions of the eye: the IRIS and CILIARY BODY in the front of the eye and the CHOROID to the back of the eye.

The iris is the colored portion of the eye. It controls the size of the PUPIL, which regulates the amount of light that enters the eye. The ciliary body lies just behind the iris and is attached to the LENS of the eye. The ciliary body produces AQUEOUS FLUID and moves the lens to focus properly. The choroid is a layer of blood vessels between the RETINA and the SCLERA, or white part of the eye. It nourishes and supports the eye.

Disorders of the uvea may include inßammations, injuries or infections. A common disorder, UVEITIS, is an inßammation of the uveal tract. It can be caused by an injury or other illness present in the body or can appear spontaneously from an

unknown cause. In addition, each section of the uvea is subject to inßammation, including IRITIS CYCLITIS and CHOROIDITIS.

uveitis An inßammation of the uveal tract of the eye. The uveal tract includes the IRIS, the CILIARY BODY, and the CHOROID. The entire tract is highly vascularized and contains the pigment melanin, which is also found in the skin. Uveitis may occur because of an injury, in connection with another disease of the eye or body, or spontaneously. The disorder is usually categorized as either anterior or posterior uveitis.

Anterior uveitis (or IRIDOCYCLITIS) occurs when the inßammation involves the iris and the ciliary body. The iris is the colored part of the eye. It controls the PUPIL, which opens and shuts to regulate the light that enters the eye. The ciliary body lies behind the iris and is connected to the LENS of the eye. The ciliary body produces AQUEOUS FLUID and moves the lens to focus the eye properly. Symptoms of anterior uveitis include redness, light sensitivity, blurred vision, and extreme pain, especially when focusing on near objects. A thorough ophthalmologic examination may be needed to determine the cause of uveitis. Additional tests such as X rays of the chest, skull or sinuses, blood tests, and examinations for arthritis or other diseases may be necessary.

Usually, a speciÞc cause for anterior uveitis is not found, and the condition is determined to have occurred spontaneously. Other diseases and disorders may cause uveitis and include arthritis, tuberculosis, SARCOIDOSIS, sinus disorders, venereal disease, ulcerative colitis, and injuries.

The prognosis for anterior uveitis is generally good, unless the eye develops complications due to recurrences. Recurrent uveitis may result in

CATARACTS or secondary GLAUCOMA due to increased intraocular pressure. Mild anterior uveitis is treated with the application of steroid eye drops to reduce the inßammation. Acute uveitis may be treated with steroid pills or injections. In both cases, cycloplegics, drops that widen the pupil, such as atropine sulfate, may be prescribed to restrict the focusing power of the inßamed eye and allow for a rest period.

Posterior uveitis involves the choroid and is also called CHOROIDITIS. The choroid is a layer of blood vessels between the RETINA and the SCLERA, or white part of the eye. The choroid nourishes and supports the eye.

Posterior uveitis is not usually as painful as anterior uveitis. There may be redness of the eye, blurred or lost vision, light sensitivity, and the appearance of ßoaters (small dark spots that seem to ßoat through the Þeld of vision). If the uveitis remains in the area of peripheral vision, the symptoms may not be noticed.

Posterior uveitis, like anterior uveitis, may occur spontaneously. It has been associated with toxoplasmosis, tuberculosis, sarcoidosis, venereal disease, viruses, and injuries. If untreated, posterior uveitis can spread from the choroid to the retina and the VITREOUS. If the inßammation involves the MACULA, permanent central vision loss may occur. When the inßammation spreads into the vitreous

and entails the center of the globe, the condition is called endophthalmitis, which may be treated with ANTIBIOTICS and possibly reversed. Treatment for posterior uveitis includes steroid eye drops or pills. In more serious cases, immunosuppressive medications may be used. (See IRITIS.)

In 1990 researchers at the University of Iowa identiÞed a gene defect that they believe is the cause of a new clinical syndrome they call hereditary uveitis. The proper name of the syndrome is autosomal dominant neovascular inflammatory vitreoretinopathy (ADNIV). Many of the features of the syndrome are common to those found in uveitis.

In 1992, researchers established that the gene that causes ADNIV is located on the long arm of chromosome 11. They are still working, however, to isolate the particular gene that they believe causes ADNIV.

venereal disease Any disease of the genitals, usually contracted by sexual contact. Some venereal diseases, or sexually transmitted diseases (STDs), such as gonorrhea, syphilis, herpes, and nongonococcal urethritis can cause eye disease and vision loss.

In the United States, gonorrhea is the second most reported communicable disease to the Centers for Disease Control and Prevention; chlamydial infections are Þrst. In 1997, there were 324,901 cases reported. This is a drop from the midto late 1980s, when nearly a million cases were reported each year. Researchers say the disease may have been more prevalent during the latter part of the 1980s because doctors were treating it with antibiotics to which the disease had become resistant. The Centers for Disease Control recommended in its 1998 Sexually Transmitted Disease Treatment Guideline that only highly effective antimicrobial agents be used to treat gonorrhea.

Gonorrhea is caused by the gonococcus bacteria and may result in blindness when contracted congenitally. The disease is passed from mother to child during birth. As the infant moves through the birth canal, the infantÕs eyes come into contact with the gonococcus bacteria growing in or near the cervix and become infected.

The infection, called gonococcal ophthalmia, or

OPHTHALMIA NEONATORUM in the case of the newborns, causes severe CONJUNCTIVITIS. First symptoms include swelling and redness of the CORNEA, CONJUNCTIVA and eyelids. Without treatment, the condition may progress to damage the cornea and result in blindness.

Adults may contract gonococcal ophthalmia by introducing the eyes to anything carrying the bacteria. Adults exhibit more serious signs of the infec-

V

tion than do infants, and may develop a severe puslike discharge. The organism may invade the cornea and cause blindness. Gonorrhea in adults may be diagnosed from a GramÕs stain or a cervical culture.

Treatment for gonococcal ophthalmia involves use of local antibiotic drops or ointments such as penicillin or tetracycline. Systemic or injected ANTIBIOTICS may also be prescribed.

At one time, congenital gonorrhea was the leading cause of blindness in children. The legislation all states requiring the administration of silver nitrate drops, or comparable antibiotics, to the eyes of all new born infants has drastically reduced its incidence.

SYPHILIS is a venereal disease caused by the spirochete Treponema pallidum. The disease may cause ocular disorders, both congenitally and after birth. Syphilis is contracted congenitally from the infected mother to the child through the womb after the fourth month of pregnancy when the spirochete can pass through the placenta. Congenital syphilis may result in vision loss and ocular impairment, deafness, dental defects, mental retardation, organ damage, and death.

Ocular damage may involve severe KERATITIS, or corneal inßammation and chorioretinal scarring. Although the infection is present at birth, the keratitis may develop later in life between ages Þve and 25. Severe keratitis may be treated with medication but may result in corneal opaciÞcation and

PHOTOPHOBIA.

Syphilis contracted after birth can cause chorioretinal scarring, IRITIS (or inßammation of the iris) and OPTIC NERVE atrophy or degeneration.

Syphilis can be diagnosed with a Wasserman test, a blood test to determine the presence of the

spirochete in the blood. An eye examination may also determine the presence of the disease and is often used to conÞrm the diagnosis.

Syphilis is treated with antibiotics, and ocular disorders are treated with medication. If treated in the early stages, the damage due to syphilis may be mild.

Congenital syphilis can be prevented if the disease of the mother is treated and controlled before the Þfth month of pregnancy. Toward this purpose, most states have developed laws that require testing for syphilis at the beginning of each pregnancy.

HERPES SIMPLEX is a virus that is accountable for most corneal blindness due to infection in the United States. Herpes simplex is one of four types of herpes virus and may infect the genitals, skin, brain, and eyes. The other types of herpes virus are herpes zoster, cytomegalovirus, and Epstein-Barr virus.

Herpes simplex virus cells usually enter the body through the mouth, genitals, or eyes. In the past, those infections that occurred above the waist were commonly referred to as Type I, and those below the waist were referred to as Type II. However, the aboveand below-the-waist categorizations are used less commonly, because Type I herpes is now frequently seen below the waist and Type II is increasingly diagnosed above the waist.

Herpes simplex may infect the eyes in one of three ways: congenitally, primarily, or recurrently. Congenital herpes is contracted by infants during birth. If the mother has active genital herpes, the infant may become exposed to the virus when the water breaks or when traveling through the birth canal.

Congenital herpes may result in permanent damage to the eyes, brain, liver, or kidneys, or in death. Ocular damage may involve the RETINA, conjunctiva, optic nerve, LENS, and cornea. Congenital herpes may be prevented by a Caesarean section birth if the mother is aware of an active herpes infection.

Primary herpes infection of the eyes is rare in adults and generally occurs only in children or adolescents. The symptoms include fever, fatigue, swollen eyelids, conjunctivitis, and a blistering rash around the eyes. The infection is usually mild and short-lived. It can be treated with antiviral eye drops or ointments.

Recurrent ocular herpes are eye infections, usually involving only one eye, that happen as a result of a reawakening of the dormant herpes virus. The virus, which may have Þrst infected the mouth, travels to the Þfth nerve ganglion, the trigeminal, where it remains dormant. The Þfth ganglion has connecting Þbers to the upper part of the face, including the eyes. On reactivation, the virus travels back up these Þbers and infects the eye.

A recurrent infection is typiÞed by redness, pain, and a watery discharge of the eye. Herpes keratitis, or corneal infection, iritis, GLAUCOMA, and CATA- RACTS may result from this infection. As the eye attempts to heal itself, corneal scarring may develop, followed by loss of vision. Each recurrence increases the possibility of scarring and vision loss.

Herpes keratitis is treated with the drugs vidarabine, TRIFLURIDINE, IDOXURIDINE, and ACYCLOVIR, antiviral eye drops or ointments. These drugs are not a cure for herpes. They stop the reproduction of viral cells but cannot rid the body of the virus. During periods of dormancy, the drugs are ineffective in Þghting the virus.

Severe scarring is treated with CORTISONE eye drops. Cortisone is a steroid that may actually worsen the herpes infection and is therefore used only for short periods of time. Severe vision loss due to scarring may in some cases be corrected with a corneal transplant, or keratoplasty.

Nongonococcal urethritis, NGU, is a venereal disease caused most often by two organisms, Chlamydia trachomatis and plasma urealyticum. NGU causes inßammation of the urethra in men and cystitis and pelvic inßammatory disease (PID) in women.

NGU may infect the eyes of adults when the eyes are exposed to the live infection, or congenitally as the infant travels through the birth canal. When the eyes become infected, conjunctivitis results. If left untreated, the infection could lead to corneal scarring and blindness. Symptoms of NGU conjunctivitis are similar to those of gonococcal conjunctivitis and include redness, swelling, and a pus discharge. Those with symptoms of NGU are given a GramÕs stain test to rule out gonorrhea. If the culture from the stain is negative for gonorrhea, treatment for NGU is prescribed. Treatment

involves local administration of antibiotics such as chlortetracycline ointment and oral antibiotics.

venous occlusion A condition that results from a blockage to a retinal vein. The disease usually involves the central retinal vein, or CRV. The damage to the RETINA occurs when blood ßows into the eye from the undamaged arteries but cannot ßow from the eye due to the blockage. Hemorrhaging and swelling occur, and vision is damaged.

The condition may occur suddenly or over a period of days. The vision may regress to 20/400 or worse, but there is rarely accompanying pain. The cause of the disease is unknown, but it is suspected that it occurs as a result of an intraluminal thrombosis, or a blood clot in the lamina cribrosa of the

OPTIC NERVE.

Because of the high occurrence of CRV obstruction and ARTERIOSCLEROSIS of the central retinal artery, it is believed that arteriosclerosis may lead to the obstruction. Open-angle GLAUCOMA, orbital or global trauma, and optic-nerve or orbital tumors may also lead to occlusion.

Treatment for venous occlusion includes therapy for the underlying cause, if apparent, and may include anticoagulation medications and photocoagulation therapy. Laser surgery may be advised to help reduce macular swelling, prevent abnormal growth of new vessels, or prevent bleeding. It is not, however, always successful. Once a venous occlusion has occurred, vision loss can be permanent. Complications of venous occlusion include neovascular glaucoma (20 percent chance), neovascularization, and RETINAL DETACHMENT.

Branch-vein occlusion occurs because the vein crosses over a hard arteriosclerotic arteriole (small part of an artery that ends in capillaries). It can cause central vision loss, neovascularization and glaucoma.

VersaBraille See PAPERLESS BRAILLE.

veterans According to the Blinded Veterans Association, there are approximately 120,000 visually impaired veterans in the United States. Many more veterans become blind or visually impaired

each year due to common eye diseases such as AGE-

RELATED MACULOPATHY, GLAUCOMA, and RETINITIS PIGMENTOSA.

The U.S. Department of Veterans Affairs (VA) provides a wide range of beneÞts to American veterans, including those with vision impairments, and their families. The vision loss does not need to occur during military service in order for a veteran to qualify for beneÞts.

Veterans who receive an honorable discharge are eligible for all beneÞts, including educational beneÞts. Those receiving general discharges qualify for all beneÞts except educational. Those who receive dishonorable and bad-conduct discharges are not eligible for veterans beneÞts. Those who receive other than honorable discharges may or may not qualify for some beneÞts. These cases are reviewed individually by the VA. Veterans rated nonservice-connected are required to complete an income questionnaire (means test) when applying for medical care and may be denied medical care depending on the results.

Those who originally enlisted after September 7, 1980, and those who entered military service after October 16, 1981, must complete the shorter of two possible terms in order to qualify for beneÞts: either 24 months of continuous active duty or the full period for which the individual was called to active duty. This does not apply to veterans with a service-connected disability or who were discharged near the end of an enlistment term because of a disability incurred or aggravated in the line of duty or due to hardship.

The U.S. Department of Veterans Affairs provides the beneÞts through three major ofÞces:

1.The Veterans BeneÞts Administration administers compensation, pensions, GI loans, insurance, education, and job-training programs, including vocational-rehabilitation and disability beneÞts. The Veterans Administration operates the Blind Rehabilitation Service, which administers programs for blinded veterans at VA Blind Rehabilitation Centers and Clinics.

2.The National Cemetery System administers death beneÞts. These include burial expenses and compensation to surviving spouses and children.

3.The Veterans Health Services and Research Administration administers health-care beneÞts, such as hospitalization, nursing-home care, domiciliary care, outpatient medical and dental treatment, beneÞciary travel, alcoholand drugdependency treatment, Agent Orange or nuclear radiation exposure treatment, prosthetic appliances, readjustment counseling centers, medical care for dependents, overseas beneÞts, appeals, and blind aids and services.

Aids and services are available to blind veterans who are eligible for medical services. Veterans are considered blind if they meet the specifications of legal blindness. Most blind veterans qualify for an annual review by the Visual Impairment Services Team (VIST), adjustment to blindness training, home improvements and structural alterations to homes, low-vision aids and training, approved electronic and mechanical aids for the blind (as well as their repair and replacement), and dog guides and the cost of the dogÕs medical care.

In order to inform blind veterans of the beneÞts available to them, Congress chartered the Blinded Veterans Association (BVA) to serve veterans with severe vision loss. The organization works through a Þeld service program and an outreach employment program to help veterans obtain services, beneÞts, rehabilitation training, and employment. (See BLINDED VETERANS ASSOCIATION and REHABILI-

TATION.)

Another group, the Blinded American Veterans Foundation (BAVF), was formed in 1985 by three American veterans who had lost their sight while serving in Korea and Vietnam. The BAVF has three primary goals: research, rehabilitation, and reemployment. It does not maintain a membership, but serves as a clearinghouse for research and educational efforts and advancements.

The BAVF supports medical research concerning blindness and other sensory disabilities, participates in outreach programs to learn the needs and concerns of veterans with sensory disabilities, and conducts informational programs directed at government, business, and the general public. It also has developed a national volunteer corps to help veterans with sensory disabilities.

The BAVF funded the research and development of the Americane, a sensory aid that has been certiÞed by the Department of Veterans Affairs and distributed to more than 2,500 blind veterans.

Contact:

The Blinded American Veterans Foundation P.O. Box 65900

Washington, DC 20035-5900 www.bavf.org

The Blinded Veterans Association 477 H Street

Northwest Washington, DC 20001-2694 202-371-8880

www.bva.org

vidarabine See ARA-A.

Viroptic See TRIFLURIDINE.

visual acuity The measurement of the amount of detail an individual sees in relation to the amount of detail someone with normal vision sees. Visual acuity is stated as an equation with 20 as the Þrst number, a slash mark and a second number of either 15, 20, 25, 30, 40, 50, 70, 100 or 200, such as 20/20. The Þrst number of the equation, 20, indicates the distance at which the measurement is taken. The second number indicates the distance at which a normally sighted person can see speciÞc detail or print.

Normal or ÒperfectÓ vision is written as 20/20. Someone with 20/20 vision sees detail at 20 feet that a normally sighted person sees at 20 feet. Someone with 20/100 vision sees detail at 20 feet that someone with normal vision could see at 100 feet.

The eye chart usually used for the visual acuity test is called the SNELLEN CHART. Using this chart as a measurement, the individual can be given a visual acuity range from 20/15 to 20/200. A measurement of 20/200 means that the individual was only able to see the largest letter on the chart, the big E.

The term count fingers refers to an individual who cannot see the big E, but who can count the number of Þngers the examiner holds up. Hand motion

is the term used to describe someone who cannot see the separate Þngers, but who can discern some movement when the hand is waved.

Light perception, or LP, describes the person who can perceive only light or its absence. NLP, or no light perception, refers to one who is unable to discern any light.

Visual-acuity measurements help describe legal definitions for blindness. These classifications determine eligibility for federal beneÞts. Someone with corrected vision of 20/50 in the better eye is classiÞed as having LOW VISION. An individual with corrected vision of 20/200 in the better eye is classiÞed as LEGALLY BLIND.

visual aids See ADAPTIVE AIDS.

visual field The area in which a person can see. This area or Þeld is measured in degrees. A person with normal vision can see objects within a Þeld of about 150 degrees with one eye and 180 degrees with both eyes when looking straight ahead. The central 60 degrees seen by both eyes is called CEN- TRAL VISION. It is also known as ÒseeingÓ vision, because it is the vision you use to look directly at something.

The vision on either side of these 60 degrees is called PERIPHERAL VISION. This is the vision surrounding what you are looking at. It describes side vision, or the things you see out of the Òcorner of your eye.Ó Peripheral vision is also called ÒtravelingÓ vision.

A loss of visual Þeld can occur in the central vision, the peripheral vision or both. An individual with a visual Þeld of 40 to 20 degrees of a possible 180 in the better eye is classiÞed as having LOW VISION. Someone with a Þeld of 20 degrees or less of the possible 180 in the better eye is classiÞed

LEGALLY BLIND.

visual impairment A term that describes a recognizable defect or malfunctioning of the eye. Impairments are diagnosed and deÞned by a medical doctor. Visual impairments range from total blindness to low vision.

The term visually impaired is also used frequently to describe those persons who have sight loss in

one or both eyes but are not legally blind. Legally blind persons have a visual acuity of 20/200 or less in the better eye after correction or a visual Þeld of less than 20 in the better eye after correction.

According to National Eye Institute, there are approximately 14 million persons who are visually impaired in the United States. That is about one in every 20 people. Worldwide, it is estimated that 135 million people are visually impaired.

The majority of visually impaired persons are male between the ages of 25 and 64. Most of those with severe impairments are female and 65 or older.

CATARACT is a leading cause of all degrees of visual impairment. Age-related macular degeneration is the leading cause of vision impairment among people who are 75 and older. It is the most common cause of new visual impairment in those 65 and older. Injury, GLAUCOMA, and congenital causes are commonly responsible for lesser impairments, whereas diabetes and cardiovascular diseases are commonly responsible for severe impairments. (See BLINDNESS.)

Prevent Blindness America. ÒAge-Related Macular Degeneration FAQ.Ó www.preventblindness.org: 2001.

National Eye Institute of the National Institutes of Health. ÒLow Vision.Ó www.nei.nih.gov/nehep/faqs.htm#2: 2000.

vitamins Vitamins are essential to the health of the eyes and maintenance of vision. Vitamin A, or retinol, is an element most closely tied to vision. The retina contains light sensitive RODS AND CONES, which receive light and provide information about the seen object. This information is converted by the RETINA to electrical impulses sent to the brain. The brain translates the impulses into an image.

The cones are responsible for central vision, detail, and color, and require light to function. The rods are responsible for peripheral vision and function in low light.

The rods contain the pigment rhodopsin, or visual purple, which is chemically very similar to vitamin A. When light strikes a rod, the rhodopsin is broken down and used up. In order to make new rhodopsin and continue to function, the rod must draw on vitamin A within the body. Without