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Abstract
Amblyopia is defined as unilateral or bilateral reduction of the best corrected central visual acuity in the absence of any organic lesion. In other words, amblyopia is a deficiency of visual acuity (form sense) occurring with an otherwise normal field of vision, color vision, and the ability to detect movement.
In addition, no structural abnormality of the fovea can be detected on ophthalmoscopy and no relative afferent pupillary defect is found unless the amblyopia is very dense.
Clinically, a visual acuity criterion has to be added. It is universally agreed that amblyopia is diagnosed as visual acuity of 6/12 or worse with an additional qualifier of one or two lines difference between the two eyes (Williams et al, 2003).
The incidence of amblyopia is nearly about 2.5% of the general population which poses a real ocioeconomic problem.
The development of visual system begins at birth and proceeds until the age of nine years when the visual system matures and become immune.
The development is accompanied by subsequent development of visual functions as visual acuity, binocular vision and others as stereopsis, Vernier acuity. Also, it is conventional to divide amblyopia into functional or organic, in clinical practice, however, amblyopia refers to the functional type (Stewart, 2005).
Recent studies proved that visual information is processed through two distinct pathways, these pathways arise from different populations of retinal ganglion cells and are defined in the lateral geniculate body into Parvocellular and Magnocellular neurons, and are also defined in the striate cortex and extrastriate cortex. Each pathway is responsible for certain visual functions.