<unk> , often abbreviated to<unk>  visual", is a term used in various Mental Health Services, Prisons and Special Schools to describe the status of a prisoner or patient who poses a threat to himself or a third party, and must therefore be kept under<unk><unk> . There are essentially two levels of<unk> s. The highest level, employed only for those patients who are considered to be extremely high risk to either themselves or a third party, involves a care worker remaining within arms reach of the service user at all times. The second level involves only maintaining a<unk>  watch on a patient, sometimes from a distance.<unk> s have been criticised by many service user groups.
Constant visual observation
Non-invasive measurement of intracranial pressure
EEG analysis
Cranial electrotherapy stimulation
Laser blended vision
Head mirror
Visual field test
Cranial auscultation