Computerized analysis of pupillograms in studies of alertness

When alert subjects sit in a quiet, darkened room for 10-15 min, their pupils remain dilated. If the subjects become sleepy or fatigued, their pupils become miotic and oscillate. Pupillometry, the recording of pupil diameter, has been used to study alertness. Pupillograms are typically graded by subjective assessment on the basis of oscillations of pupil diameter (hippus) and miosis. In this study, numeric parameters were calculated from pupillograms and were compared to subjective ratings by clinicians. Pupil diameters were recorded for 15 min at five samples per second with a custom built video pupillometer. Subjects sat in the dark and fixated a small red light. Digital filtering techniques and Fourier analysis were used to calculate several parameters designed to report hippus and miosis. The same set of pupillograms was graded by three physicians familiar with pupillometry. Grades were assigned on a scale of 1 to 4, 1 being most alert and 4 least alert. A linear combination of three of the numeric parameters had the highest correlation with the average subjective grade (r = 0.92). These techniques provide a quantitative way to evaluate pupillograms that will be used in the assessment of alertness.