functional amblyopia
Functional amblyopia is a decrease in best-corrected visual acuity, usually in one eye and rarely in both, with no organic lesion of the eye or visual pathway to account for it.1,2 Form vision deprivation, abnormal binocular interaction or both cause the loss early in life, during the years of visual immaturity.1,3
The functional amblyopias include stimulus deprivation amblyopia from media opacities or ptosis, such as congenital cataract, along with strabismic, anisometropic, refractive (isometropic) and psychogenic amblyopia.2 In strabismic amblyopia the image from the deviating eye is continually suppressed, and in anisometropic amblyopia the more ametropic eye receives a blurred image.1
Organic amblyopia, by contrast, arises from a pathological or anatomical abnormality of the retina.2 By custom the functional type is the reversible one and the organic type the irreversible one.3 Reversibility, however, depends on the age at onset of the abnormal input, its duration and the age at the start of treatment, and the boundary is therefore one of degree.3
More detail
Children are most sensitive to amblyopia in the first 2 to 3 years of life, and the sensitivity declines until visual maturation is complete at about 6 or 7 years.3 Acuity in an amblyopic eye can usually be improved up to 7 to 8 years in strabismic amblyopia, and possibly into the teens in anisometropic amblyopia with good binocular function.1 The younger the patient, the faster the likely improvement.1
In the absence of an organic lesion, a difference in best-corrected acuity of two Snellen lines or more indicates amblyopia.1 Acuity is usually better for single letters than for letters in a row, and this crowding effect is stronger in amblyopes than in normal eyes.1 Organic disease and amblyopia may coexist, so the fundi are examined before treatment begins.1
Sources (9)
- Kanski, Clinical Ophthalmology (2024), ch. 18
- Pickwell's Binocular Vision Anomalies, ch. 13
- von Noorden and Campos, Binocular Vision and Ocular Motility, ch. 14
- American Academy of Ophthalmology (2019) Amblyopia: Types, Diagnosis, Treatment, and New Perspectives. Available at: https://www.aao.org/education/disease-review/amblyopia-types-diagnosis-treatment-new-perspectiv (Accessed: 4 May 2024).
- Kushner, B.J. (2017) 'Functional Amblyopia', in Strabismus. Cham: Springer International Publishing, pp. 47–59.
- Merck Sharp & Dohme Corp. (2023) Amblyopia - Pediatrics. Available at: https://www.merckmanuals.com/professional/pediatrics/eye-defects-and-conditions-in-children/amblyopia (Accessed: 4 May 2024).
- Rowe, F.J. (2012) 'Amblyopia: Prevalence, Causes and Management', in Clinical Orthoptics. Oxford, UK: Blackwell Publishing Ltd, pp. 128–143.
- Rutstein, R., Daum, K. (1997) Anomalies of Binocular Vision: Diagnosis & Management, Mosby, pp. 347.
- Yazdani, N. et al. (2017) 'Amblyopia and refractive errors among school-aged children with low socioeconomic status in southeastern Iran', Journal of Ophthalmic & Vision Research, 12(1), pp. 17–22.
Reviewed October 2026