This is in contrast to normal sleep where both eyes are shut and both halves of the brain show unconsciousness. In USWS, also known as asymmetric slow-wave sleep, one half of the brain is in deep sleep, a form of non-rapid eye movement sleep and the eye corresponding to this half is closed while the other eye remains open.
Unlike normal sleep where both eyes are closed and both brain halves are unconscious, USWS (asymmetric slow-wave sleep) involves one brain half being deeply asleep, which is a type of non-rapid eye movement sleep. The eye associated with this half remains open while the other eye stays shut.