A device (10) and method for monitoring a subject's eyes. The device (10) includes a light source (12) producing light of a first wavelength and producing light of a second wavelength, and the device (10) includes at least one image sensor (24, 26) positioned to receive light reflected from the subject's eyes (30). The at least one image sensor (24, 26) produces a first signal indicative of light of the first wavelength and produces a second signal indicative of light of the second wavelength. The device (10) may include a controller (28) connected to the at least one image sensor (24, 26) and receiving the first and second signals. The controller (28) may subtract the first signal from the second signal and produce a third signal indicative thereof. The controller (28) may also provide a synchronization signal to the at least one image sensor (24, 26) and may also provide the signal to other components, such as the light source (12). One or more filters (16, 18) may be provided in the path of the reflected light so as to filter the light before it reaches the at least one image sensor (24, 26). One or more lens (20, 22) may also be provided to focus the reflected light before the reflected light reaches the at least one image sensor (24, 26).