Detection of sleep onset by analysis of slow eye movements: A preliminary study of MSLT recordings

Background: Excessive daytime sleepiness (EDS) adversely impacts daily activity and quality of life. Evaluation of EDS should be as easy and effective as possible. Multiple sleep latency test (MSLT) represents the standard in EDS evaluation. It is, however, a long and expensive test. Slow eye movements (SEMs) occurring at the wake-sleep transition could be an easy and reliable marker of sleepiness. We have developed an automatic method for the detection of SEMs. In the present preliminary work we compare standard measurement of EDS with visual and automatic detection of SEMs, both performed on MSLT recordings. Methods: We compared sleep latency, obtained upon standard analysis of MSLT with visually and automatically detected SEM latency, in MSLT tests performed in a population of 20 subjects, (10 Obstructive Sleep Apnea Syndrome (OSAS) patients and 10 patients with normal MSLT). Results: There were no significant differences between SEMs latency and standard determined sleep latency both in OSAS and normal MSLT patients. Automatic and visual analysis of SEMs gave comparable results. Both SEMs latency and sleep latency were significantly shorter in OSAS patients than normal MSLT patients. Conclusion: SEMs can be easily detected automatically and represent an effective marker of sleepiness in those conditions usually characterised by sleep onset with NREM sleep. Their performance equals that of standard measurements of sleep onset in MSLT recordings at least for OSAS and normal MSLT patients. Our study is, however, still preliminary and needs confirmation on a larger number of patients and in other clinical conditions characterised by EDS.