BASICS

DESCRIPTION

• Difference in refractive correction between the two eyes. More amblyogenic if difference is

– >1.50 diopters (D) hyperopic spherical equivalent

– +1.00 D cylinder

– >–6.00 D myopia

• Most common cause of amblyopia

• Two types: Spherical equivalent anisometropia and astigmatic anisometropia

EPIDEMIOLOGY

Incidence

• 25–60% of patients with anisometropia develop amblyopia (1).

• Change in anisometropia with age occurs in >15% children, yet >3D anisometropia more likely to persist (1).

Prevalence

1–11% of population (1)

RISK FACTORS

• Prematurity:

– retinopathy of prematurity

• Congenital ptosis

• Coloboma

• Lenticular opacities

• Congenital glaucoma

• Asymmetric axial growth or corneal endothelial damage

• Family history

• Any organic cause of monocular poor vision in infancy

Genetics

• No clear inheritance pattern but risk increases by proximity of other affected family members in pedigree.

• Inheritance pattern of underlying disorder prevails.

GENERAL PREVENTION

• Detection at earlier age and treatment of anisometropia can prevent amblyopia.

• Screening

• Photoscreening:

– Noncycloplegic autorefraction

– Visual acuity testing by primary care physicians and school nurses

– 14% one year olds with anisometropia had amblyopia, 40% at 2 years old, 65% at 3 years old, 76% at 5 years old (1).

PATHOPHYSIOLOGY

Amblyopia results from unequal competitive input to visual cortex resulting in a failure of development of the neuronal connections and occipital receptor cells for vision in the non-preferred eye.

ETIOLOGY

Unknown

COMMONLY ASSOCIATED CONDITIONS

• Prematurity:

– retinopathy of prematurity

• Congenital ptosis

• Coloboma

• Cataract

• Strabismus

• Microphthalmia

• Glaucoma

DIAGNOSIS

HISTORY

• Unequal glasses or contact lens prescription between eyes

• Unilateral vision deficit or ocular disorder

• Unequal eye size

PHYSICAL EXAM

• Visual acuity

• Full dilated eye examination to rule out other organic causes of unequal or subnormal vision

• Cycloplegic refraction of each eye to detect interocular difference:

– Decreased contrast sensitivity in anisometropic amblyopia

DIAGNOSTIC TESTS & INTERPRETATION

Lab

None

Imaging

Usually none required unless ruling out other organic causes of subnormal vision. May be indicated if depth of amblyopia is not proportionate to degree of anisometropia.

Diagnostic Procedures/Other

Function MRI demonstrates suppressed calcarine cortex activation at high spatial frequency and decreased activation of lateral geniculate nucleus, visual cortex from anisometropic amblyopic eye (2).

Pathological Findings

Ocular dominance width size in visual cortex is normal in anisometropia, but binocular driven cells may be reduced (1).

DIFFERENTIAL DIAGNOSIS

• Ocular or cortical pathology is responsible for reduced vision.

• Anisometropia may be caused by asymmetric axial length, lenticular refractive power, corneal refractive power, and retinal elevation.

TREATMENT

MEDICATION

No pharmacologic treatment indicated

ADDITIONAL TREATMENT

General Measures

• Refractive correction with spectacles of anisometropia

• In the presence of amblyopia, monitor vision with spectacle correction:

– Follow-up until resolution of amblyopia, or if no further improvement, begin amblyopia treatment (3).

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

• For unresolved amblyopia, occlusion of nonamblyopic eye:

– Patching from 2 to 6 h daily or atropine penalization of nonamblyopic eye (4)

– Faster improvement with greater number of hours of patching, but at 6 months equal efficacy (4)

Issues for Referral

If underlying organic cause (e.g., cataract, corneal disease, ptosis) consider referral for surgical intervention.

Additional Therapies

For high degrees of anisometropia, contact lens correction may be preferred both to reduce aniseikonia and for cosmesis.

COMPLEMENTARY & ALTERNATIVE THERAPIES

• None

• No proven efficacy of vision therapy for anisometropia

• Orthokeratology not recommended

SURGERY/OTHER PROCEDURES

Laser refractive surgery in children who fail other means of refractive correction is currently under investigation.

IN-PATIENT CONSIDERATIONS

Admission Criteria

For children extremely recalcitrant to amblyopia therapy, in-patient admission has been rarely used in some centers to facilitate initiation of treatment.

ONGOING CARE

FOLLOW-UP RECOMMENDATIONS

Patient Monitoring

• Follow-up at intervals with refractive correction to monitor improvement of vision in suspected amblyopia until no further improvement. Intervals for follow-up shorter for younger children:

– When treating amblyopia, treat with patching or atropine for intervals of 1 week for every week of age, and then check vision of each eye (including normal eye for iatrogenic amblyopia).

PATIENT EDUCATION

Focus on prevention of amblyopia

PROGNOSIS

• 2 line or greater improvement in visual acuity by spectacles alone in 77% (3)

• Resolution to 20/20 with spectacles alone in 27% (3)

• Improvement of 1.1 lines with spectacles and patching compared to 0.5 lines with spectacles alone at 5 weeks (5)

• Visual acuity improvement to 20/30 in amblyopic eye occurred with treatment in >74% (6)

COMPLICATIONS

• Occlusion amblyopia can occur in the treated eye.

• High degrees of refractive error, especially if anisometropic; if corrected by spectacles may have adverse psychosocial consequences that make wearing glasses a challenge.

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