• By: Rebecca S. Braverman, MD
    Amblyopia

    Amblyopia is defined as the reduction of best-corrected visual acuity of one or both eyes that cannot be attributed exclusively to a structural abnormality of the eye. Amblyopia develops during childhood and results in the interruption of normal cortical visual pathway development. It is clinically defined as a difference in best-corrected visual acuity of 2 or more lines of acuity between the eyes.

    Abnormal visual processing of the primary visual cortex (V1) in amblyopia reduces visual acuity and contrast sensitivity.1 A number of ophthalmic conditions can cause amblyopia including uncorrected refractive errors, strabismus, and central visual axis obstruction. Treatment of amblyopia involves correcting the underlying cause and penalization of the sound eye during the ”critical period” of brain plasticity. Traditionally, treatment was recommended for children until 8–9 years of age. Recent studies, however, suggest treatment of older individuals may be successful as the plasticity of the visual system may extend into adulthood.2 In addition, treatment that targets suppressive interactions within the visual cortex may improve both binocular and monocular visual function in children and adults with amblyopia.3

    Prevalence of Amblyopia

    The prevalence of amblyopia worldwide is approximately 1%–5%.4-7 The World Health Organization (WHO) estimates 19 million children less than 15 years of age are visually impaired; of those, 12 million are impaired due to uncorrected refractive errors and amblyopia.

    Amblyopia and Race in the United States

    Race analysis by the Vision in Preschoolers (VIP) study group of Head Start preschool children found that the prevalence of amblyopia (3.0% Asian to 5.4% non-Hispanic white) was similar among the 5 racial/ethnic groups studied. Hispanics were found to have the highest rates of astigmatism and anisometropia, whereas non-Hispanic whites had the highest rate of hyperopia.8

    Amblyopia Etiology and Risk Factors

    The etiology of amblyopia may be associated with uncorrected refractive errors, strabismus, visual axis obstruction or a combination of the above. The VIP study group recently published the risk factors associated with amblyopia in their cohort of children 3–5 years of age enrolled in the Head Start program. Strabismus, hyperopia of 2.0 diopters (D) or more, astigmatism of 1.0 D or more, or anisometropia of 0.5 D or more was present in 91% of children with unilateral amblyopia. Bilateral hyperopia of 3.0 D or more or astigmatism of 1.0 D or more was present in 76% of children with bilateral amblyopia. The authors suggested their findings were consistent with those of the Multi-Ethnic Pediatric Eye Disease Study (MEPEDS) and the Baltimore Pediatric Eye Disease Study (BPEDS).9

    Socioeconomic Impact of Amblyopia

    Information about the psychological and economic impact of amblyopia is lacking in the current body of published literature. A Cochrane database review found few randomized controlled trials to analyze the impact of living with untreated amblyopia and the cost-benefit analysis of amblyopia screening and treatment programs.10 A New Zealand study found neither amblyopia nor amblyopia treatment impacted the motor development, self-esteem or adult socioeconomic status in their cohort. Additionally, the visual deficits did not translate into important “real life” adverse outcomes.11 Another study found adults with amblyopia had mild decreased disability on utility analysis.12 Further studies have been suggested to evaluate what it means to have amblyopia and how the severity affects quality of life.13

    Useful Resources

    Anisometropic Amblyopia Learning Plan

    Amblyopia Benchmark Summary 2014

    Preferred Practice Patterns Amblyopia 2012

    Eyewiki: Amblyopia

    AAPOS Amblyopia Handouts for Families (AAPOS)

    References

    1.  Levi DM. Linking assumptions in amblyopia. Vis Neurosci. 2013 Nov;30(5-6):277-87.
    2. Levi DM. Visual processing in amblyopia: human studies. Strabismus. 2006 Mar;14(1):11-9.
    3. Hess RF, Mansouri B, Thompson B. Restoration of binocular vision in amblyopia. Strabismus. 2011 Sep;19(3):110-8.
    4. Aldebasi YH. Prevalence of amblyopia in primary school children in Qassim province, Kingdom of Saudi Arabia. Middle East Afr J Ophthalmol. 2015 Jan-Mar;22(1):86-91.
    5. Fu J, Li SM, Liu LR, et al;. Anyang Childhood Eye Study Group. Prevalence of amblyopia and strabismus in a population of 7th-grade junior high school students in Central China: the Anyang Childhood Eye Study (ACES). Ophthalmic Epidemiol. 2014 Jun;21(3):197-203.
    6. Ganekal S, Jhanji V, Liang Y, Dorairaj S. Prevalence and etiology of amblyopia in Southern India: results from screening of school children aged 5-15 years. Ophthalmic Epidemiol. 2013 Aug;20(4):228-31.
    7. Oscar A, Cherninkova S, Haykin V, et al. Amblyopia screening in Bulgaria. J Pediatr Ophthalmol Strabismus. 2014 Sep-Oct;51(5):284-8.
    8. Ying GS, Maguire MG, Cyert LA; Vision in Preschoolers (VIP) Study Group. Prevalence of vision disorders by racial and ethnic group among children participating in head start. Ophthalmology. 2014 Mar;121(3):630-6.
    9. Pascual M, Huang J, Maguire MG,et al; Vision in Preschoolers (VIP) Study Group. Risk factors for amblyopia in the vision in preschoolers study. Ophthalmology. 2014 Mar;121(3):622-9.
    10. Powell C, Hatt SR. Vision screening for amblyopia in childhood. Cochrane Database Syst Rev. 2009 Jul 8;(3):CD005020.
    11. Wilson GA, Welch D. Does amblyopia have a functional impact? Findings from the Dunedin Multidisciplinary Health and Development Study. Clin Experiment Ophthalmol. 2013 Mar;41(2):127-34.
    12. van de Graaf ES, van Kempen-du Saar H, Looman CW, Simonsz HJ. Utility analysis of disability caused by amblyopia and/or strabismus in a population-based, historic cohort. Graefes Arch Clin Exp Ophthalmol. 2010 Dec;248(12):1803-7.
    13. Rahi JS, Cumberland PM, Peckham CS. Does amblyopia affect educational, health, and social outcomes? Findings from 1958 British birth cohort. BMJ. 2006;332:820–825.