EyeMDs and Neurologist use visual fields to give us information about the nerves of the eye and the entire visual pathway. We can sometimes detect subtle nerve or brain changes or damage before a patient has any symptoms.
Understanding what your field of vision is exactly can be difficult to explain clearly or in the limited time one has with patients.
Below is a great video on what the visual field is and how it relates to the eye, the optic nerve, and it’s connection to the brain.
The later part about the LGN is likely more information than most patients need to understand.
Great article: http://www.ajnr.org/content/28/1/3/T1.expansion.html