CHAPTER 4

Amblyopia

Amblyopia is a unilateral or, less commonly, bilateral reduction of best-corrected visual acuity (also referred to as corrected distance visual acuity) that cannot be attributed directly to the effect of any structural abnormality of the eye or visual pathways. Amblyopia signifies a failure of normal neural development in the immature visual system (see Chapter 6) and is caused by abnormal visual experience early in life resulting from one of the following:

strabismus

refractive error: anisometropia or high bilateral refractive errors (isoametropia) visual deprivation

Epidemiology

Amblyopia is responsible for more cases of childhood-onset unilateral decreased vision than all other causes combined, with a prevalence of 2%–4% in the North American population. In addition, this condition is the most common cause of unilateral visual impairment in adults younger than 60 years. The prevalence of amblyopia is increased in children with a family history of amblyopia, children born prematurely, and those with developmental delay.

Detection and Screening

Amblyopic vision loss is preventable or reversible with timely detection and intervention. Thus, it is important that children with or at risk for amblyopia be identified at a young age, when the prognosis for successful treatment is best. Risk factors for amblyopia include strabismus, ocular media opacities, anisometropia, and isoametropia. Regular screening throughout childhood, whether performed in primary care offices or as part of community-based programs, allows for timely detection of vision problems, including amblyopia. Screening techniques for amblyopia vary based on the age of the child and include direct measurement of visual acuity and testing for risk factors. The latter includes corneal light reflex tests and cover testing for detection of strabismus and the Brückner test (see Chapter 7) for detection of ocular media opacities, strabismus, anisometropia, and isoametropia. Instrument-based pediatric vision screening is effective in preschool-aged and younger children. It includes the use of portable autorefraction devices to detect refractive errors and photoscreening devices, which use optical images of the eye to detect strabismus, refractive errors, and abnormalities of the red reflex.

Miller JM, Lessin HR; American Academy of Pediatrics Section on Ophthalmology; Committee on Practice and Ambulatory Medicine; American Academy of Ophthalmology; American Association for Pediatric Ophthalmology and Strabismus; American Association of Certified Orthoptists. Instrument-based pediatric vision screening policy statement. Pediatrics. 2012;130(5):983–986. Epub 2012 Oct 29.