amblyopia

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More about Amblyopia: Causes and symptoms Diagnosis Treatment Prognosis Prevention Resources

Definition

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. Generally, a difference of two lines or more (on an eye-chart test of visual acuity) between the two eyes or a best corrected vision of 20/30 or worse would be defined as amblyopia. For example, if someone has 20/20 vision with the right eye and only 20/40 with the left, and the left eye cannot achieve better vision with corrective lenses, the left eye is said to be amblyopic.

Description

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. 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. 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.

— Lorraine Steefel, RN

Dimness of vision, especially when occurring in one eye without apparent physical defect or disease. Also called lazy eye.

[New Latin amblyōpia, from Greek ambluōpiā, from ambluōpos, dim-sighted : amblus, dim + ōps, ōp-, eye; see myopia.]

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:

• Strabismus. A misalignment of the eyes is the most common cause of functional amblyopia. The two eyes are looking in two different directions at the same time. The eyes may turn in, out, up, or down. Strabismus may be diagnosed at birth, or it may develop later in childhood. The brain is sent two different images and this creates confusion. Images from the misaligned or "crossed" eye are turned off to avoid double vision.
• Anisometropia. A difference of refractive states exists between the two eyes (in other words, a difference in prescription between the two eyes). For example, one eye may be more nearsighted than the other eye, or one eye may be farsighted and the other eye nearsighted. Because the brain cannot fuse the two images, the brain suppresses the blurrier image, causing the eye to become amblyopic.
• Cataract. Clouding of the lens of the eye causes the image to be blurrier than the other eye. The brain prefers the clearer image, and the eye with the cataract may become amblyopic.
• Ptosis. If light cannot enter the eye because of the drooping lid, the eye is essentially going unused, which can lead to amblyopia. However, ptosis is rarely related to the development of amblyopia, unless the droopy eyelid completely obscures the pupil.

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:

• Patching. An opaque, adhesive patch is worn over the stronger eye for weeks to months. This therapy forces the child to use the eye with amblyopia. Patching stimulates vision in the weaker eye and aids the section of the brain that manages vision to develop more completely. Patching may be part-time or full-time. Studies in the early 2000s have shown that less time patching the eye may be as effective as more. In the case of moderate amblyopia, two hours of daily patching for four months gave the same benefit as six hours of daily patching for the same period of time. Compliance with the patching regimen was also improved with the shorter daily patching time. The treatment plan should be discussed with the doctor to determine how long the patch should be worn. When the child is wearing the patch, prescribed eye exercises may force the amblyopic eye to focus and work. This is called vision therapy or vision training. Even after the child's vision has been restored in the weak eye, part-time patching may be required over a period of years to maintain the improvement.
• Atropine. This therapy is generally reserved for children who will not wear a patch or where compliance may be an issue. A drop of a drug called atropine is placed in the stronger eye once a day to temporarily blur the vision so that the child will prefer to use the eye with amblyopia. Treatment with atropine also stimulates vision in the weaker eye and helps the part of the brain that manages vision to develop more fully.

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]

Dimness of vision not due to organic defect or refractive errors.

• hereditary a. with quadriplegia — a severe cerebellar cortical degeneration with quadriplegia at an early age has been observed in Irish setters. It is believed to be an autosomal recessive trait.

Amblyopia
Classification and external resources
ICD-10	H53.0
ICD-9	368.0
DiseasesDB	503
MedlinePlus	001014
eMedicine	oph/316
MeSH	D000550

Amblyopia, otherwise known as lazy eye,^[1] is a disorder of the visual system that is characterized by poor or indistinct vision in an eye that is otherwise physically normal, or out of proportion to associated structural abnormalities. It has been estimated to affect 1–5% of the population.^[2]

The problem is caused by either no transmission or poor transmission of the visual image to the brain for a sustained period of dysfunction or during early childhood. Amblyopia normally only affects one eye, but it is possible to be amblyopic in both eyes if both are similarly deprived of a good, clear visual image. Detecting the condition in early childhood increases the chance of successful treatment.

While the colloquialism "lazy eye" is frequently used to refer to amblyopia, the term is inaccurate because there is no "laziness" of either the eye or the amblyope involved in the condition. This term is imprecise because "lazy eye" is also a layman's term for strabismus, particularly exotropia.^{[citation needed]}

Contents 1 Physiology 2 Symptoms 3 Types 3.1 Strabismic amblyopia 3.2 Refractive or anisometropic amblyopia 3.3 Form-deprivation and occlusion amblyopia 4 Treatment and prognosis 4.1 Treatments 4.2 Clinical trials and experiments 5 See also 6 References 7 External links

Physiology

Amblyopia is a developmental problem in the brain, not an organic problem in the eye (although organic problems can induce amblyopia which persist after the organic problem has resolved).^[3] The part of the brain corresponding to the visual system from the affected eye is not stimulated properly, and develops abnormally. This has been confirmed via direct brain examination. David H. Hubel and Torsten Wiesel won the Nobel Prize in Physiology or Medicine in 1981 for their work demonstrating 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.^[4]

Symptoms

Many people with amblyopia, especially those who are only mildly so, 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 associated 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.^[5] 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.^[6] However perception of depth from monocular cues such as size, perspective, and motion parallax is normal.

Types

Amblyopia can be caused by deprivation of vision early in life by vision-obstructing disorders such as congenital cataracts, by strabismus (misaligned eyes), or by anisometropia (different degrees of myopia or hypermetropia in each eye). Ambylopia can also occur physiologically after tobacco or alcohol consumption.

Strabismic amblyopia

Main article: Strabismus

A child wearing an adhesive eyepatch to correct amblyopia

Strabismus, sometimes erroneously also called lazy eye, is a condition in which the eyes are misaligned. Strabismus usually results in normal vision in the preferred sighting (or "fellow") eye, but may cause abnormal vision in the deviating or strabismic eye due to the discrepancy between the images projecting to the brain from the two eyes.^[7] Adult-onset strabismus usually causes double vision (diplopia), since the two eyes are not fixated 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 it. 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.^[8]

Refractive or anisometropic amblyopia

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 (closer to 20/20) 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.^[9] Frequently, amblyopia is associated with a combination of anisometropia and strabismus.

Pure refractive amblyopia is treated by correcting the refractive error early with prescription lenses and patching or penalizing the good eye.

Meridional amblyopia is a mild condition in which lines are seen less clearly at some orientations than others after full refractive correction. An individual who had an astigmatism at a young age that was not corrected by glasses will later have astigmatism that cannot be optically corrected.^{[citation needed]}

Form-deprivation and occlusion amblyopia

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.^[10] 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 and prognosis

Treatments

Treatment of strabismic or anisometropic amblyopia consists of correcting the optical deficit and forcing use of the amblyopic eye, either by patching the good eye, or by instilling topical atropine in the eye with better vision. 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.^[8][11]

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.^[8]

Clinical trials and experiments

Although the best outcome is achieved if treatment is started before age 5, research has shown that children older than age 10 and some adults can show improvement in the affected eye. Children from 7 to 12 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.^[8][12]

Vision therapy programs are occasionally partially effective on motivated adults, at least in the short term.^[13]

A recent study,^[14] widely reported in the popular press,^[15] has suggested that repetitive transcranial magnetic stimulation may temporarily improve contrast sensitivity and spatial resolution in the bad eye of amblyopic adults. These results await verification by other researchers.

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.^[16]

In another recent clinical trial conducted in a hospital in China and coordinated with a research program at University of Southern California, 28 of 30 patients being treated for amblyopia showed dramatic gains with some developing 20/20 vision. The treatment involved only the use of basic computer desktop software and vision training exercises.^[17]

See also

• Eyepatch
• Convergence insufficiency
• Diplopia
• Orthoptist
• Stereoblindness
• Vision therapy

References

1. ^ "Information from your family doctor. Amblyopia ("lazy eye") in your child". American family physician 75 (3): 368. 2007. PMID 17304868. 
2. ^ Weber, JL; Wood, Joanne (2005). "Amblyopia: Prevalence, Natural History, Functional Effects and Treatment" (^{[dead link]} – ^{Scholar search}). Clinical and Experimental Optometry 88 (6): 365–375. http://www.optometrists.asn.au/gui/files/ceo886365.pdf. 
3. ^ McKee, SP., Levi, DM., Movshon, JA. (2003). "The pattern of visual deficits in amblyopia" (PDF). J Vision 4 (5): 380–405. doi:10.1167/3.5.5. http://journalofvision.org/3/5/5/McKee-2003-jov-3-5-5.pdf. 
4. ^ Jeffrey Cooper & Rachel Cooper. "All About Strabismus". Optometrists Network. http://www.strabismus.org/detection_diagnosis.html. Retrieved on 2008-03-09. 
5. ^ Hess, R.F., Mansouri, B., Dakin, S.C., & Allen, H.A. (2006). "Integration of local motion is normal in amblyopia". J Opt Soc Am a Opt Image Sci Vis 23 (5): 986–992. doi:10.1364/JOSAA.23.000986. 
6. ^ Tyler, C.W. (2004). Binocular Vision In, Duane's Foundations of Clinical Ophthalmology. Vol. 2, Tasman W., Jaeger E.A. (Eds.), J.B. Lippincott Co.: Philadelphia. 
7. ^ Levi, D.M. (2006). "Visual processing in amblyopia: human studies". Strabismus 14 (1): 11–19. doi:10.1080/09273970500536243. 
8. ^ ^{a b c d} Holmes, Repka, Kraker & Clarke (2006). "The treatment of amblyopia". Strabismus 15 (1): 37–42. doi:10.1080/09273970500536227. 
9. ^ "Commonly Missed Diagnoses in the Childhood Eye Examination". American Family Physician. August 15, 2001. http://www.aafp.org/afp/20010815/623.html. 
10. ^ Angell et al. (1981). "Visual prognosis in patients with ruptures in Descemet's membrane due to forceps injuries". Arch Ophthalmol 99 (12): 2137. doi:10.1001/archopht.99.12.2137. http://archopht.ama-assn.org/cgi/content/abstract/99/12/2137. 
11. ^ Amblyopia NEI Health Information
12. ^ Pediatric Eye Disease Investigator Group (2005). "Randomized trial of treatment of amblyopia in children aged 7 to 17 years". Archives of Ophthalmology 123 (April): 437–447. doi:10.1001/archopht.123.4.437. PMID 15824215. 
13. ^ Treatment of Amblyopia (Lazy Eye)
14. ^ Benjamin Thompson, Behzad Mansouri, Lisa Koski, and Robert F. Hess (2008). "Brain Plasticity in the Adult: Modulation of Function in Amblyopia with rTMS". Current Biology 18: 1067–1071. doi:10.1016/j.cub.2008.06.052. http://www.current-biology.com/content/article/abstract?uid=PIIS0960982208008087. 
15. ^ National Public Radio. "Magnetic Pulses To Brain Help 'Lazy Eye'". http://www.npr.org/templates/story/story.php?storyId=92965339. 
16. ^ BBC News: Video games tackle 'lazy eye'
17. ^ USC News

External links

• National Eye Institute (NEI) Resource Guide
• International Orthoptics Association
• Lazy Eye Site from the National Health Service, UK
• Optometrists Network - All About Amblyopia.
• Video with optometrist showing the options for fixing lazy eye

News articles

• IHT article on treating amblyopia in patients who are in their late teens or older
• BBC article on new study that finds lazy eye can be treated in teen years
• U.S. National Institutes of Health - Older Children Can Benefit from Treatment
• Treatment using VR software being trialed (Eastgate, et al. Nottingham University)
• Interactive Binocular Treatment for Amblyopia

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