amblyopia
Amblyopia is a reduction in best-corrected visual acuity, usually in one eye and rarely in both, for which no pathology of the eye or visual pathway can be found.1 Amblyopia is caused by form vision deprivation, abnormal binocular interaction, or both.1
Strabismic amblyopia is always unilateral.2 The visual pathways actively inhibit input from the fovea of the deviating eye, and this amblyopia can be seen as suppression carried over from binocular into monocular viewing.2 Anisometropic amblyopia can follow a refractive difference of as little as 1 diopter, and the more ametropic eye then receives a blurred image.1 Stimulus deprivation amblyopia follows media opacities such as cataract, or a ptotic lid that covers the pupil.1
Without an organic lesion, a difference of two Snellen lines or more in best-corrected acuity indicates amblyopia, and acuity is usually better with single letters than with letters in a row.1 Organic disease must be excluded before treatment.1 Refractive correction is the first step when uncorrected refractive error is the cause.3 Occlusion of the normal eye is the most effective treatment, and atropine penalization of the normal eye is an alternative.1
More detail
Bilateral ametropic amblyopia results from high, symmetrical refractive errors, usually hyperopia.1 Meridional amblyopia results from uncorrected astigmatism, usually over 1 D, that persists beyond emmetropization in early childhood.1
Treatment can usually improve acuity up to 7 or 8 years of age in strabismic amblyopia, and into the teens for anisometropic amblyopia with good binocular function.1 If acuity has not improved after 6 months of effective occlusion, further treatment is unlikely to help, and poor compliance is the single greatest barrier.1 Atropine penalization may work best in mild to moderate amblyopia of 6/24 (20/80) or better, especially from anisometropic hyperopia.1 Patching usually works faster, but atropine is hard for a child to thwart.1 Prognosis is best for pure anisometropic amblyopia and worst for mixed anisometropic and strabismic amblyopia.3
Sources (9)
- Kanski, Clinical Ophthalmology (2024), ch. 18
- von Noorden and Campos, Binocular Vision and Ocular Motility, ch. 14
- Pickwell's Binocular Vision Anomalies, ch. 13
- American Academy of Ophthalmology (2022) Amblyopia Preferred Practice Pattern®. San Francisco: American Academy of Ophthalmology.
- Ciuffreda, K.J., Levi, D.M. and Selenow, A. (1991) Amblyopia: Basic and Clinical Aspects. Boston: Butterworth-Heinemann.
- Maconachie, G.D.E. and Gottlob, I. (2015) 'The challenges of amblyopia treatment', Biomedical Journal, 38(6), pp. 510–516.
- Repka, M.X. (2002) 'Ophthalmological problems of the premature infant', Mental Retardation and Developmental Disabilities Research Reviews, 8(4), pp. 249–257.
- Rutstein, R., Daum, K. (1997) Anomalies of Binocular Vision: Diagnosis & Management, Mosby.
- Von Noorden, G.K. and Campos, E.C. (2002) Binocular Vision and Ocular Motility: Theory and Management of Strabismus. 6th edn. St. Louis: Mosby.
Reviewed October 2026