Usually none. Often discovered when decreased vision is detected via visual acuity testing of each eye individually. A history of patching, strabismus, or muscle surgery as a child may be elicited.

NOTE Amblyopia is typically unilateral, although can occur bilaterally as a result of bilateral visual deprivation (e.g., congenital cataracts not treated within the earliest months of life).

Critical

Poorer vision in one eye that is not entirely improved with refraction and not entirely explained by an organic lesion. In anisometropic amblyopia, the involved eye nearly always has a higher refractive error. The decrease in vision develops during the first decade of life. Central vision is primarily affected, while the peripheral visual field usually remains normal.

Other

Individual letters are more easily read than a full line (crowding phenomenon). In reduced illumination, the visual acuity of an amblyopic eye is reduced much less than an organically diseased eye (neutral-density filter effect).

NOTE Amblyopia, when severe, may cause a trace relative afferent pupillary defect. Care must be taken to be sure that the light is directed along the same axis in each eye, particularly in patients with strabismus. Directing the light off-axis may result in a false-positive result.

• Strabismus: Most common form (along with anisometropia). The eyes are misaligned. Vision is worse in the consistently deviating, nonfixating eye. Strabismus can lead to or be the result of amblyopia.

• Anisometropia: Most common form (along with strabismus). A large difference in refractive error (usually ≥1.50 diopters [D]) between the two eyes. Can be seen in cases of eyelid mass or congenital ptosis–inducing astigmatism.

• Isoametropia: Bilateral, large refractive errors leading to amblyopia in both eyes. Risk factors include hyperopia (>4.00–5.00 D at age >1 year), myopia (>5.00–6.00 D at any age), or astigmatism (>2.00–3.00 D at any age).

• Visual deprivation: Due to obstruction of the visual axis in one eye, leading to a preference for the other eye. This can be attributed to blepharoptosis, cataract, corneal opacification, PFV, or vitreous hemorrhage.

  • Occlusion: A subtype of visual deprivation amblyopia that occurs in the fellow eye as a result of excessive patching or atropine. Prevented by examining at appropriate intervals (1 week per year of age), patching part-time, or using the full cycloplegic refraction when using atropine.

1. History: Eye problem in childhood such as misaligned eyes, patching, or muscle surgery?

2. Ocular examination to rule out an organic cause for the reduced vision. 

3. Cover–uncover or corneal-light reflex tests to evaluate eye alignment. See Appendix 3, Cover/Uncover and Alternate Cover Tests.

4. Cycloplegic refraction of both eyes.

1. Patients younger than 12 years:

   • Appropriate spectacle correction (full cycloplegic refraction or reduce the hyperopia in both eyes symmetrically ≥1.50 D). If vision remains reduced after period of refractive adaptation (6 to 15 weeks), begin patching or penalization of fellow eye.

   • Patching: Patch the eye with better corrected vision 2 to 6 h/d (intensifying treatment if vision stops improving). Follow-up visits should be scheduled for 1 week per year of age (e.g., 3 weeks for a 3-year-old). Adhesive patches placed directly over the eye are most effective. Patches worn over glasses are not ideal due to the risk of children peeking. If a patch causes local irritation, use tincture of benzoin on the skin before applying the patch and use warm water compresses on the patch before removal.

   • Penalization with atropine: Atropine 1% once daily (used with glasses) has been shown to be equally effective as patching in mild-to-moderate amblyopia (20/100 or better). If vision does not improve, the effect of the atropine can be increased by removing the hyperopic lens from the glasses of the nonamblyopic eye. If the child is experiencing difficulty with schoolwork with the use of atropine, he/she can wear full hyperopic correction with a +2.50 bifocal during school or have the atropine drops instilled on weekends only.

   • Optical degradation: Use a high plus lens (e.g., +9.00 D or an aphakic contact lens) to blur the image. If the child is highly myopic, the minus lens from the preferred eye may be removed.

2. Continue patching until the vision is equalized or shows no improvement after three compliant cycles of patching. If a recurrence of amblyopia is likely, use part-time patching to maintain improved vision.

3. If occlusion amblyopia (a decrease in vision in the patched eye) develops, patch the opposite eye for a short period (e.g., 1 day per year of age), and repeat the examination.

4. In strabismic amblyopia, delay strabismus surgery until the vision in the two eyes is equal, or maximal vision has been obtained in the amblyopic eye.

5. If treatment of amblyopia fails or the patient presents outside of treatment age range, protective glasses should be worn to prevent accidental injury to the nonamblyopic eye. Any child who does not have vision improved to at least 20/40 needs to wear eye protection during sports (one-eyed athlete rule).

6. Treatment of cataract: Remove within the first 6 weeks of life and begin patching the nonamblyopic eye. If cataracts are bilateral, remove within the first 10 weeks of life. Initiate refractive correction for aphakic eyes as soon as possible.

7. Treatment of anisometropic amblyopia: Give the appropriate spectacle correction at the youngest age possible. If vision remains reduced after period of refractive adaptation (6 to 15 weeks), begin patching or penalization of fellow eye.

Long-term follow-up depends on the age of the patient, the amount of prescribed patching, and the severity of the amblyopia.