Generality/Definition
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Amblyopia, also known as lazy eye, is a condition in which one eye has reduced vision. Lack of brain stimulation from the weaker eye causes the strong eye to become dominant. The amblyopic eye is suppressed and may even become blind. Amblyopia may be caused by: 1- Misaligned or crossed eyes , 2- A difference in visual acuity between the two eyes (a difference of at least one line on a Snellen Visual Acuity Chart), 3- Less commonly, amblyopia develops when one eye is more nearsighted, farsighted, or astigmatic, or suffers from cataract.
Source: Amblyopia (uniteforsight.org)
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Amblyopia is an uncorrectable decrease in vision in one or both eyes with no apparent structural abnormality seen to explain it. It is a diagnosis of exclusion, meaning that when a decrease in vision is detected, other causes must be ruled out. Once no other cause is found, amblyopia is the diagnosis. Lazy eye is a common non-medical term used to describe amblyopia because the eye with poorer vision doesn't seem to be doing its job of seeing. 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. Strabismus. A misalignment of the eyes (strabismus) is the most common cause of functional amblyopia. The two eyes are looking in two different directions at the same time.
Source: Amblyopia (healthatoz.com)
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Epidemiology
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Amblyopia is the most common cause of impaired vision in children, affecting nearly three out of every 100 people or 2-4% of the population.
Source: Amblyopia (healthatoz.com)
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In the US: Prevalence of amblyopia is difficult to assess and varies in the literature, ranging from 1.0-3.5% in healthy children to 4.0-5.3% in children with ophthalmic problems. Most data show that about 2% of the general population has amblyopia while bilateral amblyopia is estimated to be around 0.5% of the population. Amblyopia was shown in the Visual Acuity Impairment Survey sponsored by the National Eye Institute (NEI) to be the leading cause of monocular vision loss in adults aged 20-70 years or older. Prevalence of amblyopia has not changed much over the years. Amblyopia occurs during the critical periods of visual development. An increased risk exists in those children who are developmentally delayed, were premature, and/or have a positive family history.
Source: Amblyopia (emedicine.com)
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Prevention
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To protect their child's vision, parents must be aware of amblyopia as a potential problem. This awareness may encourage parents to take young children for vision exams early on in life--certainly before school age. Proper nutrition is important in the avoidance of toxic amblyopia.
Source: Amblyopia (healthatoz.com)
Symptoms
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Amblyopia generally develops in young children, before age six. Its symptoms often are noted by parents, caregivers or health-care professionals. If a child squints or completely closes one eye to see, he or she may have amblyopia. Other signs include overall poor visual acuity, eyestrain and headaches.
Source: Amblyopia or Lazy Eye (allaboutvision.com)
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- frequent squinting or closing one eye to see
- poor visual acuity
- eyestrain
- headaches
- eyes do not move together or fix on the same point
- crying or complaining of an eye when one eye is covered
- cloudiness in the pupil (cataract)
- an upper eyelid that droops and covers most of the eye (ptosis)
Source: Amblyopia (uniteforsight.org)
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Diagnosis
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While a deviating eye (strabismus) may be easily spotted by the layman, amblyopia without strabismus or associated with a small deviation usually can be not noticed by either you or your pediatrician. Only an eye doctor comfortable in examining young children and infants can detect this type of amblyopia. This is why early infant and pre-school eye examinations are so necessary. The most important diagnostic tools are the special visual acuity tests other than the standard 20/20 letter charts currently used by schools, pediatricians and eye doctors. Examination with cycloplegic drops can be necessary to detect this condition in the young.
Source: Amblyopia (strabismus.org)
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There are objective methods, such as retinoscopy, to measure the refractive status of the eyes. This can help determine anisometropia. In retinoscopy, a hand-held instrument is used to shine a light in the child's (or infant's) eyes. Using hand-held lenses, a rough prescription can be obtained. 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 called the This is called 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 performed. Again, it must be emphasized that amblyopia is a diagnosis of exclusion.
Source: Amblyopia (healthatoz.com)
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Treatment
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30 years ago, it was thought that amblyopia could only be treated in children below 7 years age, however recent studies have confirmed that the treatment window can extend up to at least 17 years.
Source: Amblyopia Fact Sheet (nih.gov)
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Amblyopia can be successfully treated up to the age of 17. Early treatment is usually simple, employing glasses, drops, vision therapy and/or patching. Detection and correction before the age of two offers the best chance for a cure. Treatment of amblyopia after the age of 17 is not dependent upon age but requires more effort including vision therapy. Every amblyopic patient deserves an attempt at treatment.
Bilateral amblyopia can be treated with spectacles which improves binocular visual acuity between children aged 3 and 10years of age. A one of a kind research has been conducted in the UK using a I-BiT system which consists of a desk top viewer which is linked to a PC. Games are displayed on the PC where the screen displayed to either eye is half of the whole picture, thus forcing the brain to join these 2 images and create the whole picutre. This treatment would be especially useful for bilateral amblyopia, where patching and use of eye drops are of no help. More information on this research is found at: http://www.virart.nottingham.ac.uk/ibit/technology2.htm
Source: Amblyopia (strabismus.org)
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Amblyopic children can be treated with vision therapy (which often includes patching one eye), atropine eye drops, the correct prescription for nearsightedness or farsightedness, or surgery. Vision therapy exercises the eyes and helps both eyes work as a team. Vision therapy for someone with amblyopia forces the brain to see through the amblyopic eye, thus restoring vision. Sometimes the eye doctor or vision therapist will place a patch over the stronger eye to force the weaker eye to learn to see. Patching may be required for several hours each day or even all day long, and may continue for weeks or months.
Source: Amblyopia or Lazy Eye (allaboutvision.com)
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Surgical Care: Surgical therapy for strabismus generally should occur after amblyopia is reversed. Disadvantages to surgical therapy prior to correction of amblyopia include difficulty in telling if amblyopia is present because there is no longer a strabismus to assess fixation preference and higher potential to being lost to follow-up, as the child cosmetically looks better. The improved cosmesis gives the parents a false sense of security about the vision improving.
Source: Amblyopia (emedicine.com)
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Information for specialists
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Older Children May Benefit from Lazy Eye Treatments :
Surprising results from a nationwide study show that older children may benefit from traditional therapies for lazy eye (amblyopia), the National Eye Institute (NEI) announced. Many eyecare providers previously thought that only very young children up to about age 7 could benefit from therapies such as eye patching, eye drops, and activities for improving near vision, the NEI said. Lazy eye typically develops beginning in infancy when the eye-brain connection fails to develop properly, resulting in one eye becoming extremely dominant. The non-dominant eye in lazy eye eventually may become blind. Doctors can now feel confident that traditional treatments for amblyopia will work for many older children, NEI Director Paul A. Sieving, M.D., PhD, said in a news release. This is important because it is estimated that as many as 3% of children in the United States have some degree of vision impairment due to amblyopia. Many of these children do not receive treatment while they are young. In the study reported in the April 2005 issue of Archives of Ophthalmology, many of 507 older children ages 7-17 had vision improvement when traditional lazy eye therapies were used.
Source: Amblyopia or Lazy Eye (allaboutvision.com)
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