Amblyopia is defined as a loss of letter recognition visual acuity in the 
affected eye; however, studies in both nonhuman primates and man have shown that 
other important aspects of vision, including color, motion, and contour 
perception, are also abnormal. The anatomical changes that occur in the lateral 
geniculate nucleus and visual cortex following monocular visual deprivation 
affect both eyes and follow very different patterns with deprivation that begins 
at different ages and differ markedly in the magnocellular and parvocellular 
pathways. The interactions between the eyes and the requirements for recovery 
are very different following onset at different ages and differ for 
magnocellular and parvocellular pathways. Electrophysiological and 
psychophysical studies in man show different patterns of change in patients with 
strabismic amblyopia of early and late onset and abnormalities of color and 
motion processing that affect both amblyopic and fellow eyes and differ with age 
of onset. Abnormal visual experience also has more general effects on 
development, with amblyopic children showing abnormalities of eye-hand 
coordination when using either their amblyopic or fellow eyes, and abnormalities 
of reading. Differential effects of abnormal visual experience and treatment on 
magnocellular and parvocellular pathways may account for some of the visual 
deficits and treatment failures seen in amblyopia.