If interruptions due to nerve damage (lesions) occur on the information path from the retina to the visual centre or in the visual centre itself, then the original image can only be transmitted or processed in parts.
The affected person is now blind to the unprocessed part - he or she suffers from a loss of field of vision for this part of the image.
https://de.wikipedia.org/wiki/Anopsie (Wikipedia CC-by-sa-3.0)