BASICS

DESCRIPTION

• Decreased best-corrected visual acuity not solely attributable to organic pathology affecting one or both eyes:

– Reduction in vision occurs during the first decade of life and is reversible with treatment during this critical window of visual development.

EPIDEMIOLOGY

Incidence

It is the leading cause of monocular visual loss in young and middle-aged Americans.

Prevalence

• Affects 2–4% of North American population

• Projected lifetime risk of visual loss in patients with amblyopia is 1.2%

RISK FACTORS

• Anisometropia, odds ratio of 29 (1) – if

– >1.50 diopter (D) hyperopic spherical equivalent

– >+1.00 D cylinder

– >–6.00 D myopia

• Strabismus

• High refractive error in both eyes:

– >+5.00

– >–10.00 D

– >3.5 D cylinder

• Organic pathology uncorrected in critical window in the first decade

Genetics

• Follows the pattern of inheritance for the risk factors

• May be familial predisposition for amblyopia but no specific inheritance pattern

GENERAL PREVENTION

• Visual screening of all children during the vulnerable age period allows for detection and treatment.

– Pediatrician or family physician well child visits

– School nurses

PATHOPHYSIOLOGY

• Unequal visual competition between eyes leads to the following:

– Within the lateral geniculate nucleus, cells from the amblyopic eye atrophy

– Within the primary visual cortex, cells lose ability to respond to stimuli of one or both eyes.

ETIOLOGY

• Strabismus, 38% (2)

• Anisometropia, 37% (2)

• Combined strabismus and anisometropia, 24% (2)

• Organic pathology uncorrected in critical window of visual development

• Congenital media opacities create most dense form of amblyopia.

COMMONLY ASSOCIATED CONDITIONS

• Anisometropia

• Strabismus

• High refractive error

• Asymmetric or unilateral media opacities or other forms of visual pathway interruption

DIAGNOSIS

HISTORY

• Presence of anisometropia, strabismus, combined anisometropia and strabismus, or organic pathology that reduces vision in one eye:

– Above condition must be present during window of visual development.

– Subnormal vision unexplained on the basis of physical abnormalities in the eye and in the setting of the condition known to result in amblyopia.

PHYSICAL EXAM

• At least 2 line difference in visual acuity between eyes

• Crowding phenomenon results in reduction in vision when tested by multiple optotypes or crowding bars around isolated line of optotypes.

– Grating acuity better than expected in strabismic amblyopia

– Low contrast visual acuity better than expected in strabismic amblyopia

• Testing with single optotypes may show better vision than testing with lines of ootypes.

• Strong fixation preference in preverbal children

• Evaluation for strabismus

• Cycloplegic refraction

• Complete dilated ocular exam to rule out the presence of organic causes of visual loss

DIAGNOSTIC TESTS & INTERPRETATION

Lab

None

Imaging

• Usually none indicated unless ruling out the presence of organic central nervous system cause for subnormal vision.

• OCT may be useful in detecting subtle organic retinal or optic nerve causes of subnormal vision.

Diagnostic Procedures/Other

• Contrast sensitivity testing may be useful.

• Electrodiagnostic testing, especially multifocal electroretinography, may be useful to detect underlying organic retinal disease.

• Visual evoked potentials may be useful in detecting asymmetry or organic deficits.

• In severe amblyopia, asymmetry in the 30-lead visual evoked potential may be seen (test rarely needed).

Pathological Findings

Decrease in the cell size of the parvocellular layer of lateral geniculate nucleus laminae from amblyopic eye

DIFFERENTIAL DIAGNOSIS

• Incorrect refractive correction

• Organic pathology responsible for visual loss

• Failure to comply with patching/penalization results in uncorrected visual deficit.

TREATMENT

MEDICATION

First Line

None indicated

Second Line

L-Dopa supplementation during amblyopia treatment under investigation. Improvement of additional 2 lines with L-Dopa supplementation following standard treatment (6). Improvement in the spatial extent of visual cortex activation with stimulation of amblyopic eye with L-Dopa demonstrated on MRI (7). Proper dosage is critical due to frequent side effects of nausea and emesis.

ADDITIONAL TREATMENT

General Measures

• Treatment of etiology of amblyopia

• Refractive correction

• Correction of strabismus

• Correction of organic pathology if possible, e.g. cataract extraction, ptosis repair, corneal transplant

• Amblyopia treatment may still be needed after organic deficit corrected.

• Occlusion of nonamblyopic eye

• Comparing all-day patching to fewer hours of patching revealed faster improvement in visual acuity with greater number of hours of daily patching, but by 6 months, the differences in improvement were not statistically significant (5).

• Atropine penalization to nonamblyopic eye with spectacle correction as applicable: Requires ability to blur better eye to a visual acuity less than the amblyopic eye. Works best for hyperopic eye.

• Improvement in visual acuity 3.6 lines with atropine compared to 3.7 lines with patching at 6 months in children younger than 7 with moderate amblyopia (8)

Issues for Referral

• Refer for surgical correction of organic causes (e.g., cataract)

• May require collaboration with primary care physician regarding behavioral issues secondary to patching and patching compliance issues

Additional Therapies

• There is no additional benefit of adding near activities during amblyopia treatment (9).

• Alternatives to adhesive patch include spectacle-mounted occluder, opaque contact lens, or Bangerter foils.

• Compliance with patching may require adhesion supplements (e.g., benzoin, Tegaderm, tape) or arm immobilization.

COMPLEMENTARY & ALTERNATIVE THERAPIES

• None

• No studies prove efficacy of vision therapy.

SURGERY/OTHER PROCEDURES

Laser refractive correction under investigation in severe anisometropia in noncompliant children.

IN-PATIENT CONSIDERATIONS

Admission Criteria

In-patient admission has rarely been used to facilitate occlusion therapy in recalcitrant children.

ONGOING CARE

FOLLOW-UP RECOMMENDATIONS

Patient Monitoring

• Follow up to ensure compliance and prevent occlusion amblyopia.

• Check vision of both eyes during each visit:

– With full-time patching, follow-up interval is 1 week for every year of age to a maximum of 4 weeks.

– With part-time patching, wider intervals are acceptable but not >2–3 months. Younger children require shorter intervals.

– Consider treatment end point of full correction achieved with the normalization of vision or lack of improvement following 3 successive intervals of compliant treatment.

• Recommend taper of occlusion following maximal improvement in visual acuity (treatment end point).

PATIENT EDUCATION

• Importance of compliance with treatment

• Anticipatory guidance regarding anticipated behavioral resistance to patching and strategies for successful patching (e.g., positive reinforcement, behavioral modification)

• www.pgcfa.org

PROGNOSIS

• 82% of patients maintain increased acuity of within 10 letters after cessation of treatment (10).

• Patching 2 h daily with spectacle correction improves visual acuity 2.2 lines compared to 1.3 lines with spectacle correction alone in children 3–7 years of age (4).

• Improvement in vision of >2 lines is shown with spectacle correction alone with follow-up in 77% patients (3).

• Improvement in vision continues on average 30 weeks before stabilization (3).

• Improvement correlates with less anisometropia and better baseline visual acuity (3).

• 46% of patients achieve 20/25 or better with patching or atropine (11).

• Either 20/30 in amblyopic eye or 3 log-Mar lines of improvement in visual acuity is shown by 6 months with patching or atropine in >74%.

• Moderate amblyopia (vision better than 20/100) has better prognosis.

• Treatment prior to 7 years of age has better prognosis.

COMPLICATIONS

• Occlusion or penalization therapy can uncommonly cause visual loss (usually reversible) in the initially normal eye. Treat by decreasing or discontinuing treatment. May require switching treatment to other eye.

• Patches can cause periocular allergic skin rashes. Consider switching brands.

• Patches can cause periocular skin abrasions. Treat with micropore tape under patch or temporary discontinuation.

• Atropine may cause systemic side effects.

• Psychosocial repercussions of patching or anisometropia from atropine

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