Monitoring the Drowsiness of Drivers: A New Method Based on the Velocity of Eyelid Movements

Drowsy driving is believed to be a major cause of road crashes. However, there has been no generally accepted scale of drowsiness and no way of determining accurately what a driver's level of drowsiness was at the time of a crash. We describe here a new method, called Optalert™, for monitoring the drowsiness of drivers continuously, based on the reflectance of infrared (IR) light directed at the eyes. IR transducers are housed in a light frame such as would be worn with prescription lenses or sunglasses. New variables are described that change with drowsiness - the relative velocities of eyelid closing and opening movements during blinks, as assessed by the amplitude-velocity ratios. These variables do not require adjustment for individual subjects. The Johns Drowsiness Index, based on a combination of several weighted variables, including amplitude-velocity ratios, is introduced and is validated against different levels of impairment in the performance of a vigilance test because of drowsiness in sleep deprived volunteers. Preliminary results with Optalert™ in volunteer drivers, including commercial truck drivers, have demonstrated that dangerous levels of drowsiness can arise while driving that are not recognized at the time. The role of Optalert™ will be to warn drivers about their drowsiness when it first begins, before it reaches a dangerous level, so they can implement a strategy to deal with it before they have a drowsy crash.