Amblyopia

A visual impairment resulting from abnormal visual stimulation during early childhood, the prevalence of which ranges from 1% to 4%.

Can result from strabismus, form deprivation (e.g., due to congenital cataracts or corneal opacities), and various types of refractive errors. These errors include anisometropia (unequal refractive error between the 2 eyes), isoametropia (high but similar refractive error in the 2 eyes), and high astigmatism in 1 or both eyes.

Amblyopia due to strabismus with or without refractive error is commonly treated with initial optical correction, and subsequent patching or atropine penalization of the better-seeing eye. Amblyopia due to refractive error alone frequently responds to optical correction alone.

Amblyopia due to form deprivation is treated initially with early surgery, to remove the visual obstruction. In unilateral or asymmetric cases, patching of the better-seeing eye is necessary after surgery.

Treatment is highly successful when instituted during the infantile and preschool years, although some children as old as 13 to 17 years respond to treatment, particularly if there has been no prior therapy.

Amblyopia is a reduction of best corrected visual acuity that cannot only and directly be attributed to the effect of a structural abnormality of the eye or the visual pathways.[1]American Academy of Ophthalmology. Amblyopia Preferred Practice Pattern. Nov 2017 [internet publication]. https://www.aao.org/preferred-practice-pattern/amblyopia-ppp-2017 For the brain to learn to see with each eye, and to develop the capacity for binocular vision, each eye must have a clear and focused retinal image, and the 2 eyes must be aligned. Research has demonstrated that there are critical periods for the development of normal vision, and that amblyopia is associated with structural changes in the primary visual cortex.[2]Wiesel TN, Hubel DH. Single-cell responses in striate cortex of kittens deprived of vision in one eye. J Neurophysiol. 1963;26:1003-1017. http://jn.physiology.org/cgi/reprint/26/6/1003 http://www.ncbi.nlm.nih.gov/pubmed/14084161?tool=bestpractice.com [3]Hubel DH, Wiesel TN. The period of susceptibility to the physiological effects of unilateral eye closure in kittens. J Physiol. 1970;206:419-436. http://onlinelibrary.wiley.com/doi/10.1113/jphysiol.1970.sp009022/abstract http://www.ncbi.nlm.nih.gov/pubmed/5498493?tool=bestpractice.com