Neuroscience for Kids - Visual Pathway

Central VisualPathways

If you can understand the figureon this page, then you have learned the major pathway that visual information takes on its way from the eye to theprimary visual cortex. The figure is really not too difficult tounderstand....really.Imagine that the colored bar (half red, half blue) is in front of youreyes. The red part of the bar will project to the nasal part of yourleft retina and the temporal (lateral) part of your rightretina. The blue part of the bar will project to the nasal part ofyour right retina and the temportal (lateral) part of your leftretina. (This image is courtesy National Library ofMedicine, Bethesda, Maryland.)
Like many pathways in the nervous system, right and left visualinformation cross to the other side of the brain. This occurs in theoptic chiasm. After the optic chiasm, information about the rightvisual field (blue) is on the left side of the brain, and informationabout the left visual field (red) in on the right side. Thepathways stay this way and all the way up to the visual cortex.
Follow the blue and red lines from the eyes to see the flow ofinformation. From the retina, the first synapse isin the lateral geniculate nucleus of the thalamus.The next synapse is made in primary visual cortex inthe occiptal lobe.

The VisualPathway: From Eye to Primary Visual Cortex

What happens if there is damage to thevisual pathway? Different visualproblems will occur depending on where the damage is. The black bars(labeled 1 through 5) indicate where damage may occur and the chart to theright of the pathway indicates the resulting "blind" area (gray shading)of the visual field.
Damage at site #1: this would be like losing sight in the left eye. The entire left optic nerve would be cut and there would be a total loss of vision from the left eye.
Damage at site #2: partial damage to the left optic nerve. Here, information from the nasal visual field of the left eye (temporal part of the left retina) is lost.
Damage at site #3: the optic chiasm would be damaged. In this case, the temporal (lateral) portions of the visual field would be lost. The crossing fibers are cut in this example.
Damage at site #4 and #5: damage to the optic tract (#4) or the fiber tract from the lateral geniculate to the cortex (#5) can cause identical visual loss. In this case, loss of vision of the right side.
Partial damage to these fiber tracts can cause other predictable visual problems.

OK...did you follow this? If so, youhave come a long way in understanding how visual information gets from the eyes to the brain!! The Washington University School of Medicine has even more detail on basic visualpathways.