Amblyopia

Amblyopia

A child wearing an adhesive eyepatch to correct amblyopia
Classification and external resources
Specialty Ophthalmology
ICD-10 H53.0
ICD-9-CM 368.0
DiseasesDB 503
MedlinePlus 001014
eMedicine oph/316
Patient UK Amblyopia
MeSH D000550

Amblyopia (from Greek αμβλυωπία, "blunt vision"), also called lazy eye, is a disorder of sight.[1] It results in decreased vision in an eye that otherwise appears normal, or out of proportion to associated structural problems of the eye.

Whenever the brain does not receive visual signals from an eye for a long period of time, there is a risk of amblyopia. It also can occur when the brain "turns off" the visual processing of one eye to prevent double-vision, for example in strabismus (crossed eyes). The cause of amblyopia is within the brain.[2]

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 glasses or surgery, the better the long term outcomes.[3]

This disorder has been estimated to affect 1–5% of the population.[4] It often occurs during early childhood.

Signs and symptoms

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. People who have severe amblyopia, however, may experience related visual disorders, most notably poor depth perception. Those with amblyopia may suffer from poor visual acuity, poor spatial acuity, and low sensitivity to contrast and motion.[5] Amblyopia is characterized by several functional abnormalities in spatial vision, including reductions in visual acuity (VA), contrast sensitivity function (CSF), and vernier acuity as well as spatial distortion, abnormal spatial interactions, and impaired contour detection. In addition, individuals with amblyopia suffer from binocular abnormalities such as impaired stereoacuity (stereoscopic acuity) and abnormal binocular summation.[6] Also, a crowding phenomenon is present.[7] These deficits are usually specific to the amblyopic eye. However, sub-clinical deficits of the "better" eye have also been demonstrated.[8]

People with amblyopia also have 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.[9] Perception of depth, however, from monocular cues such as size, perspective, and motion parallax remains normal.

Types

Amblyopia has three main causes:

Strabismus amblyopia

Main article: Strabismus

Strabismus, sometimes also incorrectly called lazy eye, is a condition in which the eyes are misaligned.[10] 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.[11] 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. Recent evidence points to a cause of infantile strabismus lying with the input to the visual cortex.[12]

Those with strabismic amblyopia tend to show ocular motion deficits when reading, even when they use the nonamblyopic eye. In particular, they tend to make more saccades per line than persons with normal stereo vision, and to have a reduced reading speed, especially when reading a text with small font size.[13][14]

Strabismic amblyopia is treated by clarifying the visual image with glasses, 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 sometimes application of the eye drops 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.[15]

Refractive or anisometropic amblyopia

Refractive amblyopia may result from anisometropia (unequal refractive error between the two eyes).[16][17] Anisometropia exists when there is a difference in the power 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.[18] Given that the refractive correction of anisometropia by means of spectacles typically leads to different image magnification for the two eyes, which may in turn prevent binocular vision, a refractive correction using contact lenses is to be considered. Also pediatric refractive surgery is a treatment option, in particular if conventional approaches have failed due to aniseikonia or lack of compliance or both.[19]

Frequently, amblyopia is associated with a combination of anisometropia and strabismus. In some cases, the vision between the eyes can differ to the point where one eye has twice average vision while the other eye is completely blind.

Deprivation and occlusion amblyopia

Deprivation amblyopia (Amblyopia ex anopsia) results when the ocular media become opaque, such as is the case with congenital cataract or corneal haziness.[20] 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. Other possible causes of deprivation and occlusion amblyopia include obstruction in the vitreous and aphakia.[21] Deprivation amblyopia accounts for less than 3% of all individuals affected by amblyopia.[21]

Pathophysiology

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).[22] 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 extent of the 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.[23]

Diagnosis

Amblyopia is diagnosed by identifying a low visual acuity in one or both eyes and excluding other visual disorders as causes for the lowered visual acuity.

In young children, visual acuity is difficult to measure and can be estimated by observing the reactions of the patient reacts when one eye is covered, including observing the patient's ability to follow objects with one eye.

Stereotests like the Lang stereotest are not reliable exclusion tests for amblyopia: A patient who passes the Lang stereotest test is unlikely to have strabismic amblyopia, but could nonetheless have refractive or deprivational amblyopia.[24] It has been suggested that binocular retinal birefringence scanning may be able to identify, already in very young children, amblyopia that is associated with strabismus, microstrabismus, or reduced fixation accuracy.

It is essential to diagnose and treat amblyopia as early as possible in order to keep the vision loss to a minimum.

Treatment

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, by patching the good eye, or instilling topical atropine in the good eye, or both.[10]:130[25]

Concerning patching versus atropine, there is a drawback in using atropine: 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 amblyopia, as this can create so-called "reverse amblyopia".[15][26] Eye patching is usually done on a part-time schedule of about 4–6 hours a day. Treatment is continued as long as vision improves. It is not worthwhile continuing to patch for more than 6 months if there is no improvement.[27]

Treatment of individuals age 9 through adult is possible through applied perceptual learning.[28][29]

Deprivation amblyopia is treated by removing the opacity as soon as possible followed by patching or penalizing the good eye to encourage the use of the amblyopic eye.[15] The earlier the treatment is initiated, the easier and faster the treatment is and the less psychologically damaging. There is also a greater chance of achieving 20/20 vision if treatment is initiated as early as possible.[30]

One of the German public health insurance providers, Barmer, has changed its policy to cover, as of 1 April 2014, the costs for an app for amblyopic children whose condition has so far not improved through patching. The app offers dedicated eye exercises which the patient performs while wearing an eyepatch.[31]

Older age

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 children with amblyopia 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.[15][32]

There is tentative evidence that perceptual training may be beneficial in adults.[33][34][35]

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.[36][37]

Research

A study,[38] widely reported in the popular press,[39] has suggested that repetitive transcranial magnetic stimulation may temporarily improve contrast sensitivity and spatial resolution in the affected eye of adults with amblyopia. This approach is still under development,[40] and the results await verification by other researchers. It has also been suggested that comparable results can be achieved using different types of brain stimulation[41] such as anodal transcranial direct current stimulation[42] and theta burst rTMS.[43]

A 2013 study concluded that there is converging evidence that decorrelated binocular experience plays a pivotal role in the genesis of amblyopia and the associated residual deficits.[44] Another study of 2013[45] suggests that playing a version of the popular game Tetris that is modified such that each eye sees separate components of the game may also help to treat this condition in adults.[46] Furthermore, it has been proposed that the effects of this kind of therapy may be further enhanced by non-invasive brain stimulation[41] as shown by a recent study using anodal tDCS.[47]

A 2014 Cochrane Review sought to determine the effectiveness of occlusion treatment on patients with sensory deprivation amblyopia, however no trials were found eligible to be included in the review.[21] However, it is suggested that good outcomes from occlusion treatment for sensory deprivation amblyopia rely on compliance with the treatment.

See also

References

  1. ↑ Schwartz, editor, M. William (2002). The 5-minute pediatric consult (3rd ed.). Philadelphia: Lippincott Williams & Wilkins. p. 110. ISBN 9780781735391.
  2. ↑ Levi, D. (2013). "Linking assumptions in amblyopia.". Visual neuroscience 30 (5-6): 277–287. doi:10.1017/S0952523813000023. PMID 23879956.
  3. ↑ American Academy of Family Physicians (2007). "Information from your family doctor. Amblyopia ("lazy eye") in your child". American Family Physician 75 (3): 368. PMID 17304868.
  4. ↑ Webber, AL; Wood, Joanne (2005). "Amblyopia: Prevalence, Natural History, Functional Effects and Treatment". Clinical and Experimental Optometry 88 (6): 365–375. doi:10.1111/j.1444-0938.2005.tb05102.x. PMID 16329744.
  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 23 (5): 986–992. doi:10.1364/JOSAA.23.000986. PMID 16642175.
  6. ↑ http://www.ncbi.nlm.nih.gov/pmc/articles/PMC404107/
  7. ↑ A study of separation difficulty. Its relationship to visual acuity in normal and amblyopic eyes.
  8. ↑ Simonis K (2005). "Amblyopia Characterization, Treatment, and Prophylaxis". Survey of Ophthalmolgy 50 (2): 123–166. doi:10.1016/j.survophthal.2004.12.005.
  9. ↑ 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".
  10. 1 2 Wright, Kenneth W.; Spiegel, Peter H.; Thompson, Lisa S. (2006). Handbook of Pediatric Strabismus and Amblyopia. New York, New York: Springer. ISBN 978-0-387-27924-4.
  11. ↑ Levi, D.M. (2006). "Visual processing in amblyopia: human studies". Strabismus 14 (1): 11–19. doi:10.1080/09273970500536243. PMID 16513566.
  12. ↑ Tychsen, Lawrence (2012). "The cause of infantile strabismus lies upstairs in the cerebral cortex, not downstairs in the brainstem". Archives of Ophthalmology 130 (8): 1060–1061. doi:10.1001/archophthalmol.2012.1481.
  13. ↑ Kanonidou E., Gottlob I., Proudlock F.A. The effect of font size on reading performance in strabismic amblyopia: an eye movement investigation, Invest. Ophthalmol. Vis. Sci. 2014 January; Vol. 55, Nr. 1, pp. 451-459, doi:10.1167/iovs.13-13257.
  14. ↑ Kanonidou E, Proudlock FA, Gottlob I. Reading strategies in mild to moderate strabismic amblyopia: an eye movement investigation., Invest. Ophthalmol. Vis. Sci. 2010; Vol. 51, Nr. 7, pp. 3502-3508, doi:10.1167/iovs.09-4236.
  15. 1 2 3 4 Holmes, Repka, Kraker & Clarke (2006). "The treatment of amblyopia". Strabismus 15 (1): 37–42. doi:10.1080/09273970500536227. PMID 16513568.
  16. ↑ Robert F. Rutstein; David Corliss (April 1999). "Relationship between Anisometropia, Amblyopia, and Binocularity". Optometry & Vision Science.
  17. ↑ David R Weakley Jr. (January 2001). "The association between nonstrabismic anisometropia, amblyopia, and subnormal binocularity". Ophthalmology. pp. 163–171. doi:10.1016/s0161-6420(00)00425-5.
  18. ↑ "Commonly Missed Diagnoses in the Childhood Eye Examination". American Family Physician. August 15, 2001.
  19. ↑ William F. Astle; Jamalia Rahmat; April D. Ingram; Peter T. Huang (December 2007). "Laser-assisted subepithelial keratectomy for anisometropic amblyopia in children: Outcomes at 1 year". Journal of Cataract & Refractive Surgery 33 (12): 2028–2034. doi:10.1016/j.jcrs.2007.07.024.
  20. ↑ Angell; Robb, RM; Berson, FG; et al. (1981). "Visual prognosis in patients with ruptures in Descemet's membrane due to forceps injuries". Arch Ophthalmol 99 (12): 2137–9. doi:10.1001/archopht.1981.03930021013004. PMID 7305711.
  21. 1 2 3 Antonio-Santos A, Vedula SS, Hatt RR, Powell C (2014). "Occlusion for stimulus deprivation amblyopia". Cochrane Database Syst Rev 2: CD005136. doi:10.1002/14651858.CD005136.pub3. PMID 24504975.
  22. ↑ 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. PMID 12875634.
  23. ↑ Jeffrey Cooper & Rachel Cooper. "All About Strabismus". Optometrists Network. Retrieved 9 March 2008.
  24. ↑ Ulrich Schiefer; Helmut Wilhelm; William Hart (11 September 2007). Clinical Neuro-Ophthalmology: A Practical Guide. Springer Science & Business Media. p. 16. ISBN 978-3-540-32708-0.
  25. ↑ Coats DK and Paysse EA. Overview of amblyopia UpToDate. Last updated: Sep 25, 2014
  26. ↑ Amblyopia NEI Health Information
  27. ↑ Emmett T. Cunningham, Paul Riordan-Eva. Vaughan & Asbury's general ophthalmology. (18th ed.). McGraw-Hill Medical. ISBN 978-0071634205.
  28. ↑ Zhou, Y; et al. (2005). "Perceptual Learning Improves Contrast Sensitivity and Visual Acuity in Adults with Anisometropic Amblyopia". Vision Research 46 (5): 739–50. doi:10.1016/j.visres.2005.07.031. PMID 16153674.
  29. ↑ Polat, U; et al. (2004). "Improving Vision in Adult Amblyopia by Perceptual Learning". PNAS 101 (17): 6692–7. doi:10.1073/pnas.0401200101. PMC 404107. PMID 15096608.
  30. ↑ Williams, C; Northstone, K; Harrad, K A; Sparrow, J M; Harvey, I; Alspac Study, Team (2002). "Amblyopia treatment outcomes after screening before or at age 3 years: follow up from randomised trial". BMJ 324 (7353): 1549. doi:10.1136/bmj.324.7353.1549. PMC 116606. PMID 12089090.
  31. ↑ "App auf Rezept: Barmer bezahlt internetbasierte Behandlung" [Prescription app: Barmer pays for internet-based treatment]. www.aerztezeitung.de (in German). 28 March 2014. Retrieved 29 March 2014.
  32. ↑ 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.
  33. ↑ Polat, U; Polat, Uri; Ma-Naim, Tova; Belkin, Michael; Sagi, Dov (27 April 2004). "Improving vision in adult amblyopia by perceptual learning". PNAS 101 (17): 6692–6697. doi:10.1073/pnas.0401200101. PMC 404107. PMID 15096608.
  34. ↑ Astle, AT; Webb, BS; McGraw, PV (Nov 2011). "Can perceptual learning be used to treat amblyopia beyond the critical period of visual development?". Ophthalmic & physiological optics : the journal of the British College of Ophthalmic Opticians (Optometrists) 31 (6): 564–73. doi:10.1111/j.1475-1313.2011.00873.x. PMID 21981034.
  35. ↑ Levi DM (June 2012). "Prentice award lecture 2011: Removing the brakes on plasticity in the amblyopic brain". Optometry and Vision Science: Official Publication of the American Academy of Optometry 89 (6): 827–38. doi:10.1097/OPX.0b013e318257a187. PMC 3369432. PMID 22581119.
  36. ↑ BBC News: Video games tackle 'lazy eye'
  37. ↑ Eastgate, RM; Griffiths, GD; Waddingham, PE; Moody, AD; Butler, TKH; Cobb, SV; Comaish, IF; Haworth, SM; Gregson, R; Ash, IM and Brown, SM (2006). "Modified virtual reality technology for treatment of amblyopia". Eye 20 (3): 370–374. doi:10.1038/sj.eye.6701882. PMID 15832182.
  38. ↑ 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 (14): 1067–1071. doi:10.1016/j.cub.2008.06.052. PMID 18635353.
  39. ↑ National Public Radio. "Magnetic Pulses To Brain Help 'Lazy Eye'".
  40. ↑ Robert F. Hess; Benjamin Thompson (February 2013). "New insights into amblyopia: binocular therapy and noninvasive brain stimulation". Journal of AAPOS 17 (1). pp. 89–93. doi:10.1016/j.jaapos.2012.10.018.
  41. 1 2 Hess Robert F., Thompson Benjamin, Baker Daniel H. (2014). "Binocular vision in amblyopia: structure, suppression and plasticity". Ophthalmic and Physiological Optics 34 (2): 146–162. doi:10.1111/opo.12123.
  42. ↑ Spiegel Daniel P.; et al. (2013). "Anodal Transcranial Direct Current Stimulation Transiently Improves Contrast Sensitivity and Normalizes Visual Cortex Activation in Individuals With Amblyopia". Neurorehabilitation and neural repair 27 (8): 760–769. doi:10.1177/1545968313491006.
  43. ↑ Clavagnier Simon, Thompson Benjamin, Hess Robert F (2013). "Long lasting effects of daily theta burst rTMS sessions in the human amblyopic cortex". Brain stimulation 6 (6): 860–867. doi:10.1016/j.brs.2013.04.002.
  44. ↑ Birch, Eileen E. (2013). "Amblyopia and binocular vision". Progress in Retinal and Eye Research (Review) 33: 67–84. doi:10.1016/j.preteyeres.2012.11.001. ISSN 1350-9462. PMC 3577063. PMID 23201436.
  45. ↑ Jinrong Li; Benjamin Thompson; Daming Deng; Lily Y.L. Chan; Minbin Yu; Robert F. Hess (2013). "Dichoptic training enables the adult amblyopic brain to learn". Current Biology 23 (8): R308–9. doi:10.1016/j.cub.2013.01.059. PMID 23618662. Retrieved 28 September 2013.
  46. ↑ Joseph Nordqvist: Tetris Video Game Helps Treat Lazy Eye, Medical News Today (MNT), 23 April 2013.
  47. ↑ Spiegel Daniel P.; et al. (2013). "Transcranial direct current stimulation enhances recovery of stereopsis in adults with amblyopia". Neurotherapeutics 10 (4): 831–839. doi:10.1007/s13311-013-0200-y.

Further reading

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