A Pupillometer is disclosed. The Pupillometer has a display, an imaging apparatus that has a pupil finder and a microprocessor, and a memory in communication with the microprocessor. The display is sized to simultaneously display a video of y or more seconds in length of a left pupil and a video of y or more seconds in length of a right pupil. The pupil finder identifies the perimeter of a pupil. The imaging apparatus is capable of recording images of an individual's pupils at a rate of x image frames per second for a period of y or more seconds and playing back said image frames as a video at x image frames per second or at another rate that is faster or slower than x image frames per second. The memory has stored therein a program for enabling said microprocessor to do the following: (i) identify a center of the left pupil and a center of the right pupil for each image frame； (ii) synchronize each image frame of the two videos starting from the first frame； (iii) cause the display to display the two videos simultaneously such that each of the image frames of the video of the left eye is synchronized to a corresponding image frame of the video of the right eye when played back on the display； and (iv) cause the two videos to be displayed so that the center of the left pupil in each image frame is aligned on the display with the center of the right pupil for the corresponding image frame.
