Visual field testing is a non-invasive test which maps out the field of vision for each eye by testing how far up, down, left and right you are able to see without moving your eyes or head. It can detect if there is a dysfunction in both the central and side vision of the patient. Defects in the visual field may be caused by a number of conditions including: stroke, brain tumors and optic nerve diseases such as glaucoma. Other conditions such as retinal disease or problems associated with the eyelid may also be a reason why a visual field test is conducted.