1. A monitoring system for monitoring or predicting drowsiness of a driver of a vehicle or a machinery operator, comprising: a set of infrared or near infrared light sources, each light source arranged to direct light towards an eye of a driver or operator; the set of light sources adapted to emit light in separate time slots of a repetitive time frame, wherein the emitted light from each light source forms a virtual image of the respective light source on the cornea of the eye; an image sensor arranged such that light reflected from the eye can be captured in an image, the image sensor comprising a filter to separate light emitted by the light sources from other light in the environment; an image processing unit adapted to extract information of the light reflected from the eye; and a determining unit adapted to: determine an amplitude measure, the amplitude measure indicating an amplitude of an eye opening or eye closure, the amplitude measure being based on the extracted information of the light reflected from the eye, determine an amplitude curve based on the amplitude measures for each of the images, and determine a drowsiness index value based on the amplitude curve and a ratio between slow blinks and fast blinks.