Hi Alex,
Correct – a coma is a state of unarousable unconsciousness with no periods of wakefulness or eye opening in response to stimulation. A vegetative state (or unresponsive wakefulness syndrome) is marked by periods of wakefulness but no signs of awareness of oneself or the surroundings.
Coma is caused by disordered arousal (level of consciousness) whereas vegetative state is caused by absence of awareness (content of consciousness.
The Coma Recovery Scale-Revised (or CRS-R or JFK Coma Recovery Scale) is a standardized neurobehavioral assessment measure designed for use in individuals with disorders of consciousness. The scale is intended to be used to establish diagnosis, monitor behavioral recovery, predict outcomes, and assess treatment effectiveness. It consists of 6 subscales to assess brainstem, subcortical, and cortically mediated behaviors. The scale is intended to be administered repeatedly over time to monitor change.
The scale details how to assess each item (including auditory, visual, motor, oromotor, communication, and arousal functions). For instance, motor responses range from appropriate functional use of objects to no response to noxious stimuli. You can see the details for the assessment here: https://www.tbims.org/combi/crs/CRS%20Syllabus.pdf
Once a person with a disorder of consciousness demonstrates presence of sleep-wake cycles but lacks evidence of awareness of self and environment, they are considered to be in a vegetative state. When they have discernable and reproducible evidence of awareness of self or environment (simple command following, yes/no responses, intelligible verbalization, purposeful behavior), they are considered to be in a minimally conscious state.