refractive amblyopia


an·i·so·me·tro·pic am·bly·o·pi·a

a suppression of central vision resulting from an unequal refractive error (anisometropia) of at least 2 diopters. This induces a sufficient difference in image size (aniseikonia) that the two images cannot be fused. To avoid confusion, the blurrier image is suppressed. Synonym(s): refractive amblyopia

refractive amblyopia

Unequal vision resulting from large refractive errors between the two eyes.See also: amblyopia

amblyopia 

A condition characterized by reduced visual acuity due to a lesion in the eye or in the visual pathway, which hinders the normal development of vision, and which is not correctable by spectacles or contact lenses. The usual clinical criterion is 6/9 (or 20/30) or less in one eye, or a two-line difference or more, on the acuity chart between the two eyes. Amblyopia may occur as a result of: suppression in the deviated eye in strabismus (strabismic amblyopia; formerly called amblyopia ex anopsia, which amounts to about 20% of all cases); a blurred image in the more ametropic eye in uncorrected anisometropia (anisometropic amblyopia which amounts to about 50% of all cases); bilateral blurred images in uncorrected refractive errors (isoametropic amblyopia); a blurred image in one of the meridians of high uncorrected astigmatism (meridional amblyopia); any of the above three is also called refractive amblyopia; opacities in the ocular media (e.g. congenital cataract, severe ptosis) in infants (stimulus deprivation amblyopia or visual deprivation amblyopia or image degradation amblyopia) after the lesion has been removed; continuous occlusion of an eye as may occur in occlusion treatment (occlusion amblyopia); arsenic, lead or quinine poisoning (toxic amblyopia) or the more specific types of toxic amblyopia such as those caused by excessive use of alcohol (alcohol amblyopia), methanol (methanol amblyopia), quinine (quinine amblyopia) or tobacco (tobacco amblyopia), although the latter three may actually be due to nutritional deficiencies (nutritional amblyopia); psychological origin (hysterical amblyopia) or of unknown origin (idiopathic amblyopia).Many of these amblyopias are functional, i.e. in which no organic lesion exists as in hysterical, refractive (e.g. meridional amblyopia), isoametropic, strabismic or stimulus deprivation amblyopia. Others are organic, i.e. they are due to some pathological (e.g. congenital cataract) or anatomical anomalies (e.g. malorientation of retinal receptors), as in nutritional or toxic. However, there may be cases in which a functional amblyopia is due in part to some accompanying undetected pathology or structural defects (e.g. a change in retinal fibre layer thickness). Amblyopia occurs in 2-4% of the population. There is usually a reduction in the amplitude of accommodation in amblyopic eyes. Treatment of amblyopia depends on the type. However, the younger the patient, the more likely that the treatment will be successful. Typically, the principal treatment is occlusion of the fixating eye (or the eye with the best acuity) by patching or blurring with atropine sulfate to force the other eye to take up fixation, after full refractive correction and treatment of the underlying pathology. Other procedures (alternatives or supplemental to patching) include penalization, kicking a ball towards a specific target, playing catch a ball, bar reading, pleoptics (when there is eccentric fixation as well), and any other procedures which require fixation like drawing, duplicating letter sequences on a typewriter, cutting out patterns, etc. See cheiroscope; pinhole disc; eccentric fixation; Glasgow acuity cards; occlusion treatment; penalization; critical period; crowding phenomenon; pleoptics; suppression; bar reading test; neutral density filter test.
hysterical amblyopia Apparent loss of vision due to a psychological disorder. The patient really believes that he or she cannot see, although this is not supported by physiological impairment. The condition is often characterized by a constricted visual field or tunnel vision.
meridional amblyopia Amblyopia in one of the two principal meridians of an astigmatic eye. The amblyopia usually affects the most defocused meridian and its severity tends to vary with the amount of astigmatism. This amblyopia is of neural origin. Optical correction of the patient as young as possible usually prevents this condition. Syn. astigmatic amblyopia.