A monitoring system and method for monitoring and/or predicting drowsiness of a driver of a vehicle or a machinery operator are provided. A set of infrared, IR, or near infrared, NIR, light sources, is arranged such that an amount of the light emitted from the light source incidents on an eye of the driver or operator. The light that impinges on the eye of the driver or operator forms a virtual image of the signal sources on the eye including the sclera and/or cornea. An image sensor obtains consecutive images capturing the reflected light, wherein each image will contain glints from at least a subset or all of the light sources. A drowsiness index can be determined based on the extracted information of the glints of the sequence of images, wherein the drowsiness index indicates a degree of drowsiness of the driver or operator.