Stargardt Disease

What is Stargardt Disease?

Stargardt disease is the most common form of inherited juvenile macular degeneration. The progressive vision loss associated with Stargardt disease is caused by the death of photoreceptor cells in the central portion of the retina called the macula.

The retina is the delicate light-sensing tissue lining the back inside wall of the eye. Photoreceptor cells in the retina provide vision by conveying information from the visual field to the brain. The macula is responsible for sharp central vision — for tasks like reading, watching television, and looking at faces.

Decreased central vision is a hallmark of Stargardt disease. Side vision is usually preserved. Stargardt disease typically develops during childhood and adolescence. Also involved in Stargardt disease is a region beneath the macula called the retinal pigment epithelium.

What are the symptoms?

The symptom that brings most people to an eye doctor is a change in central vision. A doctor looking at the retina of a person with Stargardt disease will see characteristic yellowish flecks in and under the macula. The flecks might extend outward in a ring-like fashion.

The flecks are deposits of lipofuscin, a fatty byproduct of normal cell activity. In Stargardt disease, lipofuscin accumulates abnormally. The Foundation Fighting Blindness supports research studying lipofuscin build up and ways to prevent it.

A decrease in color perception also occurs in Stargardt disease. This is because photoreceptor cells involved in color perception are concentrated in the macula.

How quickly does vision fade?

The progression of symptoms in Stargardt disease is variable. Visual acuity (the ability to distinguish details and shape) may decrease slowly at first, accelerate, and then level off.
A study of 95 people with Stargardt disease showed that once a visual acuity of 20/40 is reached, there is often rapid progression of additional vision loss until it reaches 20/200. (Normal vision is 20/20. A person with 20/40 vision sees at 20 feet what someone with normal vision sees at 40 feet.) By age 50, approximately 50 percent of people in the study had visual acuities of 20/200 or worse.

Eventually, almost everyone with Stargardt disease has a visual acuity in the range of 20/200 to 20/400. The vision loss is not correctable with prescription eyeglasses, contact lenses, or refractive surgery.

Is it an inherited disease?

Stargardt disease is almost always inherited as an autosomal recessive trait. It is inherited when both parents, called carriers, have one gene for the disease paired with one normal gene. Each offspring has a 25 percent chance of inheriting two copies of the Stargardt gene (one from each parent) needed to cause the disease. Carrier parents are unaffected because they have only one copy of the gene.

Genetic counselors are an excellent resource for discussing inheritability, family planning, career choices, and other issues related to living with Stargardt disease.

In 1997, FFB-funded researchers found the gene for Stargardt disease, ABCA4, which normally causes the production of a protein involved in the visual cycle. Lipofuscin buildup appears to be related to a mutation in this gene, and the resulting production of a dysfunctional protein.

What treatment is available?

FFB is supporting several promising avenues of research, including gene and drug therapies. Researchers are planning a clinical study of a treatment that involves delivery of a healthy version of the ABCA4 gene into retinal cells to restore production of the normal protein. They are also optimistic about several drugs that may slow vision loss by reducing the buildup of lipofuscin.

Because there is some evidence that sunlight may influence lipofuscin accumulation in the retina, u-v blocking sunglasses are generally recommended for outdoors. For people who already have significant vision loss, low vision aides are available.

Are there any related diseases?

Stargardt disease is also known as Stargardt macular dystrophy or fundus flavimaculatus. In addition to recessive Stargardt disease, there are other rarer forms inherited as dominant rather than recessive traits.

Fundus Flavimaculatus

Stargardt disease, also known as fundus flavimaculatus, is usually diagnosed in individuals under the age of 20 when decreased central vision is first noticed. On examination, the retina of an affected individual shows a macular lesion surrounded by yellow-white flecks, or spots, with irregular shapes. The retina consists of layers of light-sensing cells that line the inner back wall of the eye and are important in normal vision. The macula is found in the center of the retina and is responsible for the fine, detailed central vision used in reading and color vision.

Stargardt - Risk Factors

Stargardt disease, an early-onset form of macular degeneration, is an inherited disease. The condition is programmed into your cells at conception. It is not caused by injury, infection or exposure to a toxic agent. Because Stargardt disease is an inherited condition, there is nothing that can be done to reduce the risk of developing the disease.

However, recent findings in rodent models of Stargardt disease find that unprotected, prolonged exposure to light can accelerate vision loss. Therefore, The Foundation Fighting Blindness strongly recommends that patients with Stargardt wear brimmed hats or visors and sunglasses when outdoors.

Stargardt disease is an autosomal recessive disease. In autosomal recessive diseases, unaffected parents, who are carriers, have one gene with a disease-causing mutation paired with one normal gene. Each of their children then has a 25 percent chance (or 1 chance in 4) of inheriting the two diseased genes (one from each parent) needed to cause the disorder. Carriers are unaffected because they have only one copy of the gene.

Usher Syndrome

What is Usher Syndrome?

Usher syndrome is an inherited condition characterized by hearing impairment and progressive vision loss. The vision loss is due to retinitis pigmentosa (RP), a degenerative condition of the retina, and usually appears during adolescence or early adulthood. Balance may also be affected. Symptoms vary from person to person and progress at different rates.

Researchers funded by The Foundation Fighting Blindness (FFB) are studying causes and potential treatments for Usher syndrome and other retinal degenerative diseases. Excellent progress in research has been made recently

What are the symptoms?

There are at least three different forms of Usher syndrome. People with Usher syndrome type 1 (USH1) are born completely deaf and experience problems with balance. The first signs of RP — night blindness and loss of peripheral vision — usually appear in early adolescence.

In Usher syndrome type 2 (USH2), newborns have moderate to severe hearing impairment. Symptoms of RP typically start shortly after adolescence. Visual problems progress less rapidly than in Usher type 1 and hearing loss usually remains stable.

A rarer third type of Usher syndrome (USH3) was documented in 1995. Children with USH3 are usually born with good or only mild impairment of hearing. Their hearing and vision loss is progressive, starting around puberty. Balance may be affected.

Hearing loss in Usher syndrome is due to a genetic mutation (alteration) affecting nerve cells in the cochlea, a sound-transmitting structure of the inner ear. The same genetic defect also adversely affects photoreceptor cells in the retina, leading to vision loss. The retina is a delicate tissue in the back of the eye composed of light-sensing photoreceptor cells. These cells — also known as rods and cones — are responsible for converting light into electrical impulses that transfer messages to the brain.

How is Usher syndrome inherited?

Usher syndrome is passed from parents to their offspring through an autosomal recessive inheritance pattern. In this type of inheritance, two copies of a mutated gene, one from each parent, are required for the child to be affected. A person with only one copy of the gene is a “carrier” and rarely has any symptoms. Genetic counselors are excellent resources for discussing inheritability, family planning, genetic testing, and other related issues.

About 20,000 people in the U.S. have Usher syndrome. Worldwide, it is the leading cause of combined deafness and blindness. Approximately 30 percent of people with RP report some degree of hearing loss, and about half of them are diagnosed with Usher syndrome. Genetic testing may soon be available to help people define their condition and the risk of other family members or future offspring being affected.

What treatment is available?

Intensive research is under way to discover the causes of, and treatments for, all forms of RP. Researchers have found numerous genetic variations causing Usher syndrome, allowing for the designation of a variety of subtypes (i.e., 1A, 1B, IC, 1D, 1E, 1F, 1G, 2A, 2B, 2C, and 3A). Gene therapy to replace defective Usher genes is being studied in preclinical settings.

Researchers have also identified a nutritional therapy to slow the rate of vision loss in some RP patients. Although not a cure, they found that vitamin A palmitate can slow retinal degeneration in some people with RP and Usher syndrome type 2. They also showed that docosahexaenoic acid (DHA) — an omega-3 fatty acid — can enhance the effect of vitamin A. However, the enhanced benefit of DHA was realized only during the first two years of vitamin A therapy. (Only adult RP and USH2 patients were studied, so the effect in other patients with Ushers Syndrome is not known.) FFB can provide you with the recommendations of the study’s author.

A Phase II/lll human clinical trial is underway to test encapsulated cell technology (ECT) for delivery of a vision-preserving, therapeutic agent (ciliary neurotrophic factor or CNTF) to the retina. Preliminary results from the phase I study of the ECT-CNTF treatment were highly encouraging. Other therapeutic agents are showing promise in pre-clinical studies.

In addition, numerous researchers are experimenting with artificial retinal implants. The devices are placed on the surface of the retina and restore rudimentary, functional vision.

Researchers are also making excellent progress in gene therapy to treat Usher syndrome. With gene therapy, a normal gene is delivered to the retina to replace the mutated, disease-causing gene. The gene therapy may also be used to treat hearing loss.

Retinal cell transplantation is another area of growing interest. In these potential treatments, transplanted retinal cells would replace retinal cells lost to RP and other retinal degenerative diseases.

Are there any related diseases?

Other conditions, some of which are also inherited, can result in deafness and deaf-blindness but are not related to Usher syndrome. However, the RP associated with Usher syndrome shares most of its characteristics with other forms of RP. Researchers expect that advances in understanding and treating other forms of RP will directly benefit people with Usher syndrome, and vice versa.

Usher Syndrome - Risk Factors

Recent research findings suggest that in some forms of retinal degeneration, prolonged, unprotected exposure to sunlight may accelerate vision loss. Therefore, The Foundation recommends that patients wear sunglasses and brimmed hats or visors when outdoors.

Some women feel that their vision loss progressed more rapidly during pregnancy. However, the effect of pregnancy on Usher syndrome has not been clinically studied.

Usher syndrome is an inherited, genetic disease. It is caused by mutations in genes that are active in the retina and in the ear. Gene mutations are programmed into your cells at the time of conception. Usher syndrome is not caused by injury, infection or exposure to any toxic substance.

Usher syndrome is an autosomal recessive disease. In autosomal recessive diseases, unaffected parents, who are carriers, have one gene with a disease-causing mutation paired with one normal gene. Each of their children then has a 25 percent chance (or 1 chance in 4) of inheriting the two diseased genes (one from each parent) needed to cause the disorder. Carriers are unaffected because they have only one copy of the gene.

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Retinitis Pigmentosa

What is Retinitis Pigmentosa?

Retinitis pigmentosa (RP) refers to a group of inherited diseases causing retinal degeneration. The cell-rich retina lines the back inside wall of the eye. It is responsible for capturing images from the visual field. People with RP experience a gradual decline in their vision because photoreceptor cells (rods and cones) die.

Forms of RP and related diseases include Usher syndrome, Leber’s congenital amaurosis, rod-cone disease, Bardet-Biedl syndrome, and Refsum disease, among others.

Normal vision

As seen by a person with retinitis pigmentosa

What are the symptoms?

Symptoms depend on whether rods or cones are initially involved. In most forms of RP, rods are affected first. Because rods are concentrated in the outer portions of the retina and are triggered by dim light, their degeneration affects peripheral and night vision. When the more centrally located cones — responsible for color and sharp central vision — become involved, the loss is in color perception and central vision.

Night blindness is one of the earliest and most frequent symptoms of RP. People with mainly cone degeneration, however, first experience decreased central vision and ability to discriminate color.

RP is typically diagnosed in adolescents and young adults. It is a progressive disorder. The rate of progression and degree of visual loss varies from person to person. Most people with RP are legally blind by age 40, with a central visual field of less than 20 degrees in diameter. It is a genetic disorder and, therefore, is almost always inherited.

How is RP inherited?

An estimated 100,000 people in the U.S. have RP, mainly caused by mutated genes inherited from one or both parents. Mutated genes give the wrong instructions to photoreceptor cells, telling them to make an incorrect protein, or too little or too much protein. (Cells need the proper amount of particular
proteins in order to function properly.) Many different gene mutations exist in RP. In Usher syndrome, for example, at least 14 disease-causing genes have been identified.

Genetic mutations can be passed from parent to offspring through one of three genetic inheritance patterns — autosomal recessive, autosomal dominant, or X-linked. In autosomal recessive RP, parents who carry the gene but have no symptoms themselves could have some children who are affected and others who are not. Similarly, in autosomal dominant RP, an affected parent could have affected and unaffected children. In families with X-linked RP, only males are affected; females carry the genetic trait but do not experience serious vision loss.

If a family member is diagnosed with RP, it is strongly advised that other members of the family also have an eye exam by a physician who is specially trained to detect and treat retinal degenerative disorders. Discussing inheritance patterns and family planning with a genetic counselor can also be useful.

What treatments are available?

The Foundation Fighting Blindness (FFB) has funded many important RP research and clinical advances. A nutritional therapy using vitamin A and docosahexaenoic acid (DHA) has emerged as an effective treatment for many patients; gene therapies are progressing through preclinical trials; technologies for delivering therapeutic agents to rod and cone cells are being studied in Phase II/lll clinical studies; an implantable microchip to enhance retinal function is under development. Details are available on FFB’s Web site, www.FightBlindness.org, or by calling 1-800-683-5555.

Although not a treatment for RP, it is also important to know that low vision aids are useful for maintaining independence. Low vision specialists can make personalized recommendations for mechanical, optical, electronic, and computer-based low vision products.

What testing is available?

Genetic testing is available for RP. It helps assess the risk of passing the disorder from parent to offspring. It also helps with attaining an accurate diagnosis. A patient with an accurate diagnosis is in a better position to keep track of new findings, research developments, and treatment approaches.

However, not all RP-causing genes have been discovered. If a person chooses to get genetically tested, there is about a 50 percent chance that their disease-causing gene will be identified.

Retinitis Pigmentosa - Risk Factors

Recent research findings suggest that in some forms of Retinitis Pigmentosa, prolonged, unprotected exposure to sunlight may accelerate vision loss. Therefore, The Foundation recommends that patients wear sunglasses and visors when outdoors.

Some women feel that their vision loss progressed more rapidly during pregnancy. However, the effect of pregnancy on Retinitis Pigmentosa has not been clinically studied.

Retinitis Pigmentosa is an inherited, genetic disease. It is caused by mutations in genes that are active in retinal cells. Gene mutations are programmed into your cells at the time of conception. Retinitis Pigmentosa is not caused by injury, infection or exposure to any toxic substance.

There are three common inheritance patterns: autosomal dominant, autosomal recessive, and X-linked.

In autosomal dominant forms of Retinitis Pigmentosa, an affected person has one gene with a mutation causing the disease paired with one healthy, normal gene. When the affected person has children with an unaffected partner, there is a 50 percent chance that the affected parent will pass the disease-causing gene to each child. The unaffected partner will only pass normal genes. In dominant diseases, a child who does not have the disease gene will not have the disease and cannot pass the disease to his or her children.

In autosomal recessive forms of Retinitis Pigmentosa, unaffected parents, who are carriers, have one gene with a disease-causing mutation paired with one normal gene. Each of their children then has a 25 percent chance (or 1 chance in 4) of inheriting the two diseased genes (one from each parent) needed to cause the disorder. Carriers are unaffected because they have only one copy of the gene.

In X-linked forms of Retinitis Pigmentosa, the gene for the disease is located on the X chromosome. Females have two X chromosomes and can carry the disease gene on one of these X chromosomes. Because they have a healthy version of the gene on their other X chromosome, X-linked diseases typically do not affect females. Sometimes, however, when carrier females are examined, the retina shows minor signs of the disease.

Males have only one X chromosome paired with one Y chromosome and are therefore genetically susceptible to X-linked diseases. Males cannot be carriers of X-linked diseases. Males affected with an X-linked disease always pass the gene on the X chromosome to their daughters, who then become carriers. Affected males never pass an X-linked disease gene to their sons because fathers pass the Y chromosome to their sons.

Female carriers have a 50 percent chance (or 1 chance in 2) of passing the X-linked disease gene to their daughters, who become carriers, and a 50 percent chance of passing the gene to their sons, who are then affected by the disease.

It is important to remember that because Retinitis Pigmentosa is an inherited disorder, it commonly affects other members of a family. If someone in your family is diagnosed with a retinal degeneration, it is strongly advised that all members of the family contact an eye care professional.

Macular Degeneration

What is Age-Related Macular Degeneration?

Age-related macular degeneration (AMD) is a retinal degenerative disease that causes a progressive loss of central vision. AMD is the most common cause of vision loss in individuals over 55. An estimated nine million people in the U.S. either have AMD or are at substantial risk of developing it.

What are the symptoms?

The macula is a small region in the center of the retina, which enables a person to see fine detail. Light sensing cells in the macula, known as photoreceptors, convert light from the visual field into electrical impulses and then transfer the impulses to the brain via the optic nerve. Central vision loss from AMD occurs when photoreceptor cells in the macula degenerate.

People with AMD may first notice a blurring of central vision, especially during tasks such as reading or sewing. Also, straight lines may appear distorted or warped. As the disease progresses, blind spots may form within the central visual field. In most cases, if one eye has AMD, the other eye will develop the disease. The extent of central vision loss varies depending on the type of AMD — dry or wet.

Normal vision

Picture as seen by someone who has macular degeneration

What is dry AMD?

Dry AMD accounts for about 90 percent of all cases, and normally affects vision less than wet AMD. Dry AMD is sometimes called atrophic, nonexudative, or drusenoid macular degeneration. A characteristic of dry AMD is the accumulation of tiny protein and fat-containing “drusen” deposits in a thin layer of cells beneath the photoreceptors in the retina called Bruch’s membrane. The origin of drusen is unknown, but they may be from waste products of various cells and tissues of the retina. Drusen may interfere with the health of the macula, causing progressive degeneration of the photoreceptor cells. Drusen deposits can, however, be present without vision loss.

Reduction in central vision from dry AMD occurs gradually over many years. Vision may even remain stable between eye examinations. People with dry AMD do not usually experience a total loss of central vision but tasks that require finely focused vision may become more difficult.

Research suggests that medium- and large-sized drusen present a greater risk for the progression of dry AMD to wet AMD. Wet AMD causes more severe vision loss. Although no standard therapies currently exist to treat dry AMD, several clinical research trials are evaluating methods, including laser treatments, to reduce their size.

What is wet AMD?

Wet AMD accounts for about 10 percent of all cases of macular degeneration. Wet AMD is also called choroidal neovascularization (CNV), subretinal neovascularization, or exudative or disciform degeneration. In wet AMD, abnormal blood vessels grow beneath the macula. These vessels leak blood and fluid into the macula that damage photoreceptor cells. Wet AMD often progresses rapidly and can cause substantial loss of central vision.

What treatments are available for wet AMD?

Excellent progress is being made in understanding, predicting, and treating wet AMD. Scientists have discovered new causes of the disorder — including genetic and environmental factors — as well as possible risk indicators. Numerous pharmaceutical companies are developing wet AMD treatments. Researchers are also studying cell transplantation to preserve and/or restore vision.

In June 2006, the FDA approved a drug called Lucentis for the treatment of wet AMD. Results from a large, two-year study showed that Lucentis halted vision loss in more than 90 percent of individuals with the wet form of age-related macular degeneration (AMD). In addition, Lucentis restored vision in 33 percent of those study participants. FFB has funded dozens of research projects to better understand the mechanisms that lead to vision-robbing blood vessel growth in wet AMD, giving companies like Genentech, maker of Lucentis, clear targets for the development of AMD treatments.

Numerous clinical research trials are being conducted to evaluate other promising treatments for wet AMD.

If you have been diagnosed with wet AMD, visit www.FightBlindness.org for a list of treatments and clinical trials. FFB recommends that patients always discuss study participation with a health care provider before enrolling.

How does nutrition affect AMD?

The Age-Related Eye Disease Study (AREDS), conducted by the National Eye Institute, revealed that a dietary supplement containing a combination of vitamins and minerals could help reduce the risk of advanced wet AMD and vision loss in people who are at greatest risk.

The AREDS study found that high levels of antioxidants and zinc can reduce the risk of developing advanced AMD by about 25 percent. The specific daily amounts of antioxidants and zinc used by the study researchers were 500 milligrams of vitamin C; 400 International Units of vitamin E; 15 milligrams of beta-carotene (often labeled as equivalent to 25,000 International Units of vitamin A); 80 milligrams of zinc as zinc oxide; and two milligrams of copper as cupric oxide. Copper was added to the AREDS formulations containing zinc to prevent copper deficiency anemia, a condition associated with high levels of zinc intake. Please visit www.nei.nih.gov/amd for more information about the AREDS recommendations.

AMD may also be related to dietary fat, according to scientists studying people with early- and intermediate-stage disease. They found that study subjects who reported eating lower amounts of vegetable and animal fat were less likely to develop advanced AMD.

However, fish and nuts can slow the progress of AMD. Studies have revealed that eating fish — which is high in healthful omega-3 fatty acids — has a protective effect. Though nuts are also protective, researchers did not determine which nuts, or how much of them, should be consumed.

Carotenoids are also possible protectors against AMD. Researchers found that the more dietary lutein and zeaxanthin — two carotenoids found in green and colorful vegetables — you eat, the lower the likelihood you have of developing advanced AMD. These carotenoids are highly concentrated in the macula and may be protecting it from damage.

What are the risk factors?

The exact causes of both dry and wet AMD are not completely understood. However, genetics, diet, cigarette smoking, bright sunlight, cardiovascular disease, and hypertension are considered to be possible risk factors for AMD.

Is AMD an inherited disease?

Researchers are discovering that genetics appears to be a major factor in more than half of the cases of AMD. In March 2005, three independent research groups — including one funded by FFB — discovered a gene called Complement Factor H (CFH) that appears to be linked to at least 50 percent of all cases of AMD. Prior to this landmark discovery, FFB-funded researchers discovered other genes that appeared to be linked to AMD, though these genes were implicated in a smaller number of cases than CFH.

What is the Amsler grid?

Along with regular examinations by an eye doctor, people can evaluate their eyesight for possible symptoms of AMD using a simple home testing device known as the Amsler grid. The Amsler grid, consisting of parallel and perpendicular lines, looks much like a sheet of graph paper. By focusing on a marked spot in the middle of the grid, it is quite easy to detect blurred or distorted vision. While the Amsler Grid is not a substitute for an expert medical diagnosis, it does allow people to check their eyesight regularly for possible symptoms of AMD. To receive a free Amsler Grid, please call the Foundation Fighting Blindness.

What low-vision aids are available?

As central vision declines, people with AMD may benefit from low-vision aids like magnifying glasses and special lenses, screens that enlarge small print, text-to-speech and speech-to-text computer software programs, and any number of other specialized technologies. Low-vision experts can also help individuals adapt daily living skills. Low-vision specialists are available through ophthalmology centers and physician referrals.

Common eye problems

Short sight (myopia) and long sight (hypermetropia) are common conditions, both caused by the cornea and lens not focusing properly on the retina.

Short sight is where the eyeball is elongated or the lens is too thick, causing the image to focus in front of the retina.

Short sight means that the image is focused in front of the retina

Long sight is where the eyeball is too short or the lens too thin, causing the image to focus behind the retina.

Long sight means that the image is focused behind the retina

How we see?

The images we see are made up of light reflected from the objects we look at. This light enters the eye through the cornea. Because this part of the eye is curved, it bends the light, creating an upside-down image on the retina (this is eventually put the right way up by the brain).

	Focusing on a nearby object	Focusing on a distant object

What happens when light reaches the retina?

The retina is a complex part of the eye, but only the very back of it is light-sensitive. This part of the retina has roughly the area of a 10p coin, and is packed with photosensitive cells called rods and cones. These allow us to see images in colour and detail, and to see at night.

Cones are the cells responsible for daylight vision. There are three kinds - each responding to a different wavelength of light: red, green and blue. The cones allow us to see in colour and detail.

Rods are responsible for night vision. They are sensitive to light but not to colour. In darkness, the cones do not function at all.

Focusing the image

The lens focuses the image. It can do this because it is adjustable - using muscles to change shape and help us focus on objects at different distances. The automatic focusing of the lens is a reflex response and is not controlled by the brain.

Sending the image to the brain

Once the image is clearly focused on the sensitive part of the retina, energy in the light that makes up that image creates an electrical signal. Nerve impulses can then carry information about that image to the brain through the optic nerve.

Low vision

What is low vision?

Specialist teacher Manju helps Sam Raj, who has low vision, at school © Fabienne Fossez / Sightsavers

Low vision is when, even after medical treatment, people have difficulty distinguishing objects and/or distances. People with low vision can be helped by changes made to their environment, such as painting the edges of stairs white so they can be seen more easily, or specially made devices.

Measuring low vision

Eye care specialists measure sight against a standard known as '20/20' vision. This based on what most people are able to see on a standard eye-test chart at a distance of 20 feet (in metres this is called 6/6 vision). If you can read the chart at 20 feet you have 20/20 or 'normal' vision.

The range of low vision:

• in mild cases of low vision, someone looking at a standard eye chart from 6 feet away will see what somebody with 'normal' or 20/20 vision sees from 18 feet away
• in extreme cases, low vision means that a person standing 3 feet from the eye chart will see the equivalent of what a person with 'normal' vision will see 60 feet away
• if someone's sight is any worse than this, they are classified as blind.

Low vision is officially defined as 'anybody who has an optimum corrected vision of less than 6/18 to 3/60 in their better eye'.

'Optimum corrected vision' means the 6/18 to 3/60 vision is enabled the aid of standard corrective visual devices - usually spectacles.

Many diagnosed with low vision can be helped by surgical treatment, and do not need low-vision aids. Even people with less than 3/60 vision can be helped.

Refractive error

A child has his eyes examined at school, Pakistan. © Jamshyd Masud / Sightsavers

Refractive error is an eye disorder meaning the shape of the eye does not bend light correctly, resulting in a blurred image. The disorder can be simply diagnosed, measured and corrected with spectacles, yet approximately 8.2 million people remain functionally blind due to uncorrected refractive error.

Sightsavers works in several ways to improve the vision of people with refractive error:

• screening: we identify individuals with poor vision which can be improved by spectacles or other optical devices. Last year we screened over 2 million people for refractive error.
• refraction: we evaluate the patient to determine what spectacles or device may be required.
• manufacture: we manufacture spectacles or an appropriate device and provide to those in need.

Common refractive errors:

• short sight (myopia)
• long sight (hypermetropia)
• Aging of the lens (presbyopia)
• Irregular curvature of the lens (astigmatism)
  

Low vision

Some people are still severely visually impaired even after correction, but their visual function can be greatly improved with the use of visual and non-visual aids.

Low vision aids

Visual aids

Visual aids for improving low vision work for those with visual capability of more than 1/60 (ie people who can see at a range of one foot what people with 'normal' vision would see at a range of 60 feet).

There are several types of low-vision device. Each works on particular form of low vision. Prescription is just the first step - it is also essential to motivate and train people to use the devices properly.

Visual aids include those that:

• help people seeing things close up. These are particularly useful for reading and to help children whose education would otherwise suffer. These include hand-held magnifying glasses and specially made, powerful spectacles.
• help people see things in the distance. These include telescopes.
• Technical enhancements such as closed circuit television, computer scanners and high tech image magnifiers.

Magnifiers

Some magnifiers can be made relatively easily and cheaply in optical workshops. Sometimes people in poorer countries use 'modified' plastic drainpipes fitted with a lens which acts as an effective reading aid.

Some studies show that over a third of children with low vision who cannot read would be able to with a simple magnifier.

Non-visual aids

Non-visual aids are often modifications to homes and everyday tools and equipment that make them low-vision friendly. These modifications are often quite cheap and easy to make.

Non-visual aids include:

• tilted desks for children, meaning they don't have to bend over flat desks to read text close-up.
• contrasting colours. A meal of rice and boiled fish can be difficult to distinguish for a low-vision person if served on a white plate. Certain colours and backgrounds can be combined to make text easier to read.
• size. Providing large felt tip pens or charcoal for children to write with, or using a photocopier to enlarge printed materials.
• lighting. Low-vision people needing more light can sit closer to windows or have better-positioned artificial light. People needing less light can benefit from dark glasses or large-brimmed hats.
• lines. A good way to aid mobility is through well-defined, contrasting-coloured lines to mark the edge of paths or steps.