IOP elevation in different phases of sleep

Large and significant increases in intraocular pressure (IOP) have previously been demonstrated after as little as 30 minutes of sleep.¹² The present experiment tests the hypothesis that the lack of eye movements during sleep is responsible for this increase in IOP. Nine subjects slept in the laboratory on two separate nights. IOP was measured (with subjects in the supine position) using a Keeler Pulsair noncontact tonometer. Eye movements were monitored using electro-oculography. Subjects were woken from sleep after 60–90 minutes, on one night when they were in rapid eye movement (REM) sleep, and on one night when they were not. IOP increased significantly on both nights, but the differences between these increases was not significant. Thus, mechanical factors associated with lack of eye movements do not appear to contribute to the increase in IOP after sleep.