Patients with field defects that are severe enough to endanger their driving licenses often claim that they easily can compensate for their defects by actively looking around. The display may help to demonstrate how demanding, erratic and time-consuming searching eye movements may be.
Arguably, an "egocentric" representation, that is, a simulation where the background view moves relative to a stationary fixation point, may be more realistic. Click the to open such simulation a in a separate window. Place the cursor near the fixation point and use small cursor movements to induce background movements. Again, the movement will be erratic when attempting to look in the direction of a field defect. Hold down the shift key to over-ride this feature.
Like all other patients with visual field defects, those who suffer from homonymous defects will experience problems with depth perception. Although perimetric maps may suggest that binocular vision is possible within an extended area on the normal side (to the left in this representation of a right homonymous hemianopia), a visual space plot reveals that the binocular region is quite restricted (yellow area in the diagram). Binocular vision cannot take place either inside or outside the fixation point, which regions are covered by one eye only. It is easy to understand that critical depth judgements near the fixation point will be very difficult. Everyday examples include the handling of cutlery and the cutting of nails.
Left-click on the display to start an aura simulation expanding left-ward from the center. Right-click to make the aura expand towards the right. The animation can be stopped in flight by clicking again.
The display may be particularly useful when evaluating a first attack of a possible aura, where the patient commonly finds it difficult to describe details that are important for the diagnosis. Ask the patient if he or she does or does not recognize any of the features shown in the display. A negative answer is a strong indication for considering other mechanisms, including
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