Swinging flashlight test or Marcus Gunn test is one of the most basic eye exams that neurologists, ophthalmologists, optometrists and primary care doctor perform when visiting most of their patients. The doctor asks her patient to look ahead then shines a penlight first toward one eye, then the other, alternating quickly to observe patient’s pupils’ response to the light. In case if both pupils do not show a similar response to the light stimuli, shone in one eye at a time, the patient will be diagnosed with RAPD or Marcus Gunn pupils. The results of this simple yet very important test help doctors in early diagnosis of many important eye related diseases such as optic neuropathy and multiple sclerosis.