An alertness monitoring system uses reflectance measurement of infrared lightpulses to monitor eye movement of a vehicle or machine operator. The data isused to measure eye and eyelid movement for presence slow or drifting eyemovements, and/or eyelid closure and optionally one or more of, absence ofsaccadic movement, loss of eye co-ordination, wavering eyelids, partial eyeclosure, and drooping eyelids as indicators of loss of attention anddrowsiness. The eye movements of a subject are analysed using reflected infrared light to obtain measures of the blink amplitude velocity ratio and thesaccade amplitude velocity ratio. The readings are continuously compared witheye movement data indicative of degrees of alertness which correlate to bloodalcohol content values so that the monitor provides an indication of theoperator's legal fitness to operate the vehicle or machine from the point ofview of drowsiness no matter how it is caused.
