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American Heritage Dictionary:
am·bly·o·pi·a |
[New Latin amblyōpia, from Greek ambluōpiā, from ambluōpos, dim-sighted : amblus, dim + ōps, ōp-, eye; see myopia.]
amblyopic am'bly·o'pic (-ō'pĭk, -ŏp'ĭk) adj.|
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Gale Encyclopedia of Children's Health:
Amblyopia |
Definition
Amblyopia refers to diminished vision in either one or both eyes, for which no cause can be discovered upon examination of the eye. Amblyopia is the medical term used when the vision in one of the eyes is reduced because the eye and the brain are not working together properly. The eye itself looks normal, but it is not being used normally because the brain is favoring the other eye. This condition is also sometimes called lazy eye.
Description
Lazy eye is a common non-medical term used to describe amblyopia because the eye with poorer vision does not seem to be doing its job of seeing. Amblyopia is the most common cause of impaired vision in childhood. It affects approximately two or three out of every 100 children. Vision is a combination of the clarity of the images of the eyes (visual acuity) and the processing of those images by the brain. If the images produced by the two eyes are substantially different, the brain may not be able to fuse the images. Instead of seeing two different images or double vision (diplopia), the brain suppresses the blurrier image. This suppression can lead to amblyopia. During the first few years of life, preferring one eye over the other may lead to poor visual development in the blurrier eye. Unless it is treated successfully in early childhood, amblyopia usually persists into adulthood and is the most frequent cause of monocular (one eye) visual impairment among children.
Demographics
The prevalence of amblyopia is difficult to assess, with estimates ranging from 1.0 to 3.5 percent in healthy children to 4.0 to 5.3 percent in children with other vision problems. It is seen in similar numbers in both sexes and in all races.
Causes and Symptoms
Amblyopia may be caused by any condition that adversely affects normal visual development or use of the eyes. All babies are born with poor eyesight. As babies grow, however, their eyesight usually progresses. Good eyesight needs a clear, focused image that is the same in both eyes. If the image is not clear in one eye, or if the image is not the same in both eyes, the vision pathways will not develop as they should. In fact, the pathways may actually worsen. Anything that blurs the vision or causes the eyes to be crossed during childhood may cause amblyopia. Some of the major causes of amblyopia are as follows:
Barring the presence of strabismus or ptosis, children may or may not show signs of amblyopia. Children may position their heads at an angle while trying to favor the eye with normal vision. They may have difficulty seeing or reaching for things when approached from the side of the amblyopic eye. Parents should see if one side of approach is preferred by the child or infant. If an infant's good eye is covered, the child may cry.
When to Call the Doctor
Parents should call the doctor if their child demonstrates any signs associated with amblyopia, including the appearance of crossed eyes, lazy eye, a drooping eyelid, difficulty seeing, or if the child seems to favor one side of approach over the other. However, since children do not always show symptoms of amblyopia, it is important to get their eyes examined at or before the age of three and no later than age five, while the disorder is more easily treated.
Diagnosis
It is not easy to recognize amblyopia. A child may not be aware of having one strong eye and one weak eye. Unless the child has a misaligned eye or other obvious abnormality, there is often no way for parents to tell that something is wrong. Because children with outwardly normal eyes may have amblyopia, it is important to have regular vision screenings performed for all children. While there is some disagreement regarding the age children should have their first vision examination, their eyes can, in actuality, be examined at any age, even on the first day of life.
Some people recommend that children have their vision checked by their pediatrician, family physician, ophthalmologist, or optometrist at or before six months of age. Others recommend testing by at least the child's fourth birthday. There may be a critical period in the development of vision, and amblyopia may not be treatable after age eight or nine. The earlier amblyopia is found, the better chance there is for a positive outcome. Most physicians test vision as part of a child's medical examination. If there is any sign of an eye problem, they may refer a child to an eye specialist.
There are objective methods, such as retinoscopy, by which to measure the refractive status of the eyes. This form of examination can help diagnose anisometropia. In retinoscopy, a hand-held instrument is used to shine a light in the child's (or infant's) eyes. While the doctor uses hand-held lenses, he can obtain a rough prescription. Visual acuity can be determined using a variety of methods. Many different eye charts are available (e.g. tumbling E, pictures, or letters). In amblyopia, single letters are easier to recognize than when a whole line is shown. This is referred to as the "crowding effect" and helps in diagnosing amblyopia. Neutral density filters may also be held over the eye to aid in the diagnosis. Sometimes visual fields to determine defects in the area of vision will be performed. Color vision testing may also be done. Again, it must be emphasized that amblyopia is a diagnosis of exclusion. Various medical problems can also cause a decrease in vision. An examination of the eyes and visual system is very important when there is an unexplained decrease in vision.
Treatment
Amblyopia treatment is most effective when done early in the child's life, usually before age seven. It is important that any anisometropia and refractive problems be treated initially, because sometimes amblyopia can be resolved with glasses alone.
The next step is to make the child use the eye with the reduced vision (weaker eye). As of 2004, there are two ways to do this:
Prognosis
The younger the child, the better the chance for improvement with occlusion and vision therapy. Success in the treatment of amblyopia also depends on the amblyopia's severity, its specific type, and the child's compliance with treatment. It is important to diagnose and treat amblyopia early because significant vision loss can occur if it is left untreated. The best outcomes result from early diagnosis and treatment.
Prevention
Early recognition and treatment of amblyopia in children can help to prevent permanent visual deficits. All children should have a complete eye examination at least once between age three and five to avoid the risk of allowing unsuspected amblyopia to go beyond the age where it can be treated successfully.
Nutritional Concerns
There are some rarer forms of amblyopia caused by various nutritional deficiencies. In these cases, the doctor recommends the proper diet and perhaps supplementation in order to resolve the problem.
Parental Concerns
It is vital that parents bring their child for an eye exam sometime between the ages of three and five to prevent amblyopia from becoming untreatable.
Resources
Books
Barber, Anne. Infant and Toddler Strabismus and Amblyopia, Vol. 41, No. 2: Behavioral Aspects of Vision Care. Santa Ana, CA: Optometric Extension Program Foundation, 2000.
Fielder, Alistair, et al. Amblyopia: A Multidisciplinary Approach. Kent, UK: Elsevier—Health Sciences Division, 2002.
Pratt-Johnson, John A., et al. Management of Strabismus and Amblyopia: A Practical Guide. New York: Thieme Medical Publishers, 2000.
Periodicals
Dutton, Gordon N., and Marie Cleary. "Should We Be Screening for and Treating Amblyopia? Evidence Shows Some Benefit." British Medical Journal 327, no. 7426 (November 29, 2003): 1242–44.
Finn, Robert. "Less Patching Fine for Amblyopia in Young Children: Two Studies." Family Practice News 34, no. 9 (May 1, 2004): 70–71.
Organizations
American Association for Pediatric Ophthalmology and Strabismus. PO Box 193832, San Francisco, CA 94119–3832. Web site: www.aapos.org.
National Eye Institute. 31 Center Drive MSC 2510, Bethesda, MD 20892–2510. Web site: www.nei.nih.gov.
Prevent Blindness America. 500 E. Remington Road, Schaumburg, IL 60173. Web site: www.preventblindness.org.
Web Sites
"Amblyopia." National Eye Institute, June 2004. Available online at www.nei.nih.gov/health/amblyopia (October 16, 2004).
[Article by: Deanna M. Swartout-Corbeil, RN Lorraine Steefel, RN]
Saunders Veterinary Dictionary:
amblyopia |
Dimness of vision not due to organic defect or refractive errors.
Random House Word Menu:
categories related to 'amblyopia' |
Wikipedia on Answers.com:
Amblyopia |
 |
This article may be too technical for most readers to understand. Please help improve this article to make it understandable to non-experts, without removing the technical details. The talk page may contain suggestions. (November 2009) |
| Amblyopia | |
|---|---|
| Classification and external resources | |
| ICD-10 | H53.0 |
| ICD-9 | 368.0 |
| DiseasesDB | 503 |
| MedlinePlus | 001014 |
| eMedicine | oph/316 |
| MeSH | D000550 |
Amblyopia, also known as lazy eye,[1] is a disorder of the visual system that is characterized by a vision deficiency in an eye that is otherwise physically normal, or out of proportion to associated structural abnormalities of the eye. It has been estimated to affect 1–5% of the population.[2]
Amblyopia means that visual stimulation either fails to transmit or is poorly transmitted through the optic nerve to the brain for a continuous period of time. It can also occur when the brain "turns off" the visual processing of one eye, to prevent double-vision, for example in strabismus (crossed-eyes). It often occurs during early childhood, resulting in poor or blurry vision. Amblyopia normally affects only one eye in most patients. However, it is possible, though rare, to be amblyopic in both eyes, if both fail to receive clear visual images. Detecting the condition in early childhood increases the chance of successful treatment, especially if detected before the age of five. The earlier it is detected, and the underlying cause corrected with spectacles and/or surgery, the more successful the treatment in equalizing vision between the two eyes.
The colloquialism "lazy eye" is frequently used to refer to amblyopia. The term "lazy eye" is imprecise because it is a layman's term for strabismus, particularly exotropia.[3]
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Amblyopia is a developmental problem in the brain, not any intrinsic, organic neurological problem in the eyeball (although organic problems can lead to amblyopia which can continue to exist after the organic problem has resolved by medical intervention).[4] The part of the brain receiving images from the affected eye is not stimulated properly and does not develop to its full visual potential. This has been confirmed by direct brain examination. David H. Hubel and Torsten Wiesel won the Nobel Prize in Physiology or Medicine in 1981 for their work in showing the irreversible damage to ocular dominance columns produced in kittens by sufficient visual deprivation during the so-called "critical period." The maximum "critical period" in humans is from birth to two years old.[5]
Many people with amblyopia, especially those who only have a mild form, are not even aware they have the condition until tested at older ages, since the vision in their stronger eye is normal. However, people who have severe amblyopia may experience related visual disorders, most notably poor depth perception. Amblyopes may suffer from poor spatial acuity, low sensitivity to contrast and some "higher-level" deficits to vision such as reduced sensitivity to motion.[6] These deficits are usually specific to the amblyopic eye. Amblyopes also suffer from problems of binocular vision such as limited stereoscopic depth perception and usually have difficulty seeing the three-dimensional images in hidden stereoscopic displays such as autostereograms.[7] However, perception of depth from monocular cues such as size, perspective, and motion parallax remains normal.
Amblyopia can be caused by deprivation of vision early in life by vision-obstructing disorders such as congenital cataracts, by strabismus (misaligned eyes), anisometropia (different degrees of myopia or hypermetropia in each eye), or by a significant amount of astigmatism in one or both eyes.
Strabismus, sometimes incorrectly also called lazy eye, is a condition in which the eyes are misaligned.[8] Strabismus usually results in normal vision in the preferred sighting (or "fellow") eye (the eye that the person prefers to use), but may cause abnormal vision in the deviating or strabismic eye due to the difference between the images projecting to the brain from the two eyes.[9] Adult-onset strabismus usually causes double vision (diplopia), since the two eyes are not fixed on the same object. Children's brains, however, are more neuroplastic, and therefore can more easily adapt by suppressing images from one of the eyes, eliminating the double vision. This plastic response of the brain, however, interrupts the brain's normal development, resulting in the amblyopia. Strabismic amblyopia is treated by clarifying the visual image with glasses, and/or encouraging use of the amblyopic eye with an eyepatch over the dominant eye or pharmacologic penalization of the better eye. Penalization usually consists of applying atropine drops to temporarily dilate the pupil, which leads to blurring of vision in the good eye. This helps to prevent the bullying and teasing associated with wearing a patch, although application of the eyedrops is more challenging. The ocular alignment itself may be treated with surgical or non-surgical methods, depending on the type and severity of the strabismus.[10]
Refractive amblyopia may result from anisometropia (unequal refractive error between the two eyes). Anisometropia exists when there is a difference in the refraction between the two eyes. The eye which provides the brain with a clearer image typically becomes the dominant eye. The image in the other eye is blurred, which results in abnormal development of one half of the visual system. Refractive amblyopia is usually less severe than strabismic amblyopia and is commonly missed by primary care physicians because of its less dramatic appearance and lack of obvious physical manifestation, such as with strabismus.[11] Frequently, amblyopia is associated with a combination of anisometropia and strabismus.
Form-deprivation amblyopia (Amblyopia ex anopsia) results when the ocular media become opaque, such as is the case with cataracts or corneal scarring from forceps injuries during birth.[12] These opacities prevent adequate visual input from reaching the eye, and therefore disrupt development. If not treated in a timely fashion, amblyopia may persist even after the cause of the opacity is removed. Sometimes, drooping of the eyelid (ptosis) or some other problem causes the upper eyelid to physically occlude a child's vision, which may cause amblyopia quickly. Occlusion amblyopia may be a complication of a hemangioma that blocks some or all of the eye.
Treatment of strabismic or anisometropic amblyopia consists of correcting the optical deficit (wearing the necessary spectacle prescription) and often forcing use of the amblyopic eye, either by patching the good eye, or by instilling topical atropine in the eye with better vision.[13] Yet, there is a drawback as the drops can have a side-effect of creating nodules in the eye which a correctional ointment can counteract. One should also be wary of over-patching or over-penalizing the good eye when treating for amblyopia, as this can create so-called "reverse amblyopia" in the other eye.[10][14]
Treatment of individuals age 9 through adult is possible through applied perceptual learning.[15][16]
Form deprivation amblyopia is treated by removing the opacity as soon as possible followed by patching or penalizing the good eye to encourage use of the amblyopic eye.[10] The earlier treatment is initiated, the easier and faster the treatment is and the less psychologically damaging.[citation needed] There is also a greater chance of achieving 20/20 vision if treatment is initiated as early as possible.[17]
Although the best outcome is achieved if treatment is started before age 8, research has shown that children older than age 12 and some adults can show improvement in the affected eye. Children from 9 to 11 who wore an eye patch and performed near point activities (vision therapy) were four times as likely to show a two line improvement on a standard 11 line eye chart than amblyopic children who did not receive treatment. Adolescents aged 13 to 17 showed improvement as well, albeit in smaller amounts than younger children. It is uncertain whether such improvements are only temporary, however, particularly if treatment is discontinued.[10][18]
For adults, a 2004 study published in PNAS demonstrated that perceptual learning can be used to improve the vision of amblyopic adults.[19]
Virtual reality computer games where each eye receives different signals of the virtual world that the player's brain must combine in order to successfully play the game have shown some promise in improving both monocularity in the affected eye as well as binocularity.[20][21]
A recent study,[22] widely reported in the popular press,[23] has suggested that repetitive transcranial magnetic stimulation may temporarily improve contrast sensitivity and spatial resolution in the affected eye of amblyopic adults. These results await verification by other researchers.
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
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 | American Heritage Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved. Read more |
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| Gale Encyclopedia of Children's Health. © 2006 by The Gale Group, Inc. All rights reserved. Read more |
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| Saunders Veterinary Dictionary. Saunders Comprehensive Veterinary Dictionary 3rd Edition. Copyright © 2007 by D.C. Blood, V.P. Studdert and C.C. Gay, Elsevier. All rights reserved. Read more |
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| Random House Word Menu. © 2010 Write Brothers Inc. Word Menu is a registered trademark of the Estate of Stephen Glazier. Write Brothers Inc. All rights reserved. Read more |
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| Wikipedia on Answers.com. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article Amblyopia. Read more |
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