The visual field test is a way to evaluate the peripheral vision sensitivity of an eye. It uses a very small test light that can vary in brightness. This determines how well and how far out to the side this small intensity of light can be seen.he visual field test is a way to evaluate the peripheral vision sensitivity of an eye. It uses a very small test light that can vary in brightness. This determines how well and how far out to the side this small intensity of light can be seen.