The visual pathway

One important feature of the visual pathway is that it tries to preserve positional information of the visual field. To understand this more simply, we can liken it to moving a jigsaw. If you had just proudly completed a 1000-piece jigsaw puzzle on your kitchen table and wanted to move it to a different location, throwing it up into the air and hoping it will all fall back into place would be an inefficient and risky strategy; pieces may get lost and it would take time to put back together again. Instead, if you carefully moved the jigsaw as a whole and made sure that pieces remained adjacent in transit, then it would be much quicker and easier to view in its new location.

The visual system works using a similar principle with the entirety of the visual field being the complicated jigsaw. Parts of the visual field that fall adjacent to one another, for example, the words on this page, will be processed adjacent to each other along the visual pathway and in the brain itself.

This means that if a patient presents with a visual field defect (or scotoma), we can use what we know about the visual pathway and the positional preservation of the visual field to predict where problems along the pathway may be occurring.

If a patient presents with a visual field defect (or scotoma), we can use what we know about the visual pathway and the positional preservation of the visual field to predict where problems along the pathway may be occurring

In the visual pathway (Figure 1 and 2), lightning bolts are used to indicate the location of damage that would cause the example field defects shown alongside. In the figures, defects (blind spots) are shown as black shapes, and clear vision is represented as the appropriate colours for each eye. The eyes are shown individually because if a defect only affects one eye, or it affects both eyes differently, then it can be a further clue as to the location of the damage.