Your visual field is how wide of an area you can see when focusing on a central point.  A visual field test is a way Dr. Dietrich can measure how much vision you have in either eye or how much vision loss has occurred over time. 

A visual field test can also determine if you have any blind spots in your vision and where they are located.  Dr. Dietrich is also able to determine if there has been any vision loss from diseases such as glaucoma or various eyelid disorders such as ptosis or droopy eyelids.  Other conditions that can be associated with blind spots are retinal disease, optic neuropathy, brain tumors, or stroke.