PVS & Eye Tracking: Schiavo, apparently, can track objects with her eyes, which suggests her diagnosis of PVS is more complicated than media accounts have suggested (recall as well Terri's husband won't let her have MRI testing done even though it can detect the brain lesions associated with PVS):

Eye tracking and Emotional responses are the most common ways of determining whether a patient is responding, and therefore no longer in a vegetative state. The first sign of a patient emerging from PVS is the localizing of the eyes on a visual stimulus. This can be observed because persons in a vegetative state are unable to track moving objects or fixate their vision on an object, and as a patient recovers they regain this ability. This type of a response if most often detected by family members or caregivers that have worked directly with the patient. Eye tracking is not necessarily enough to show that a person is recovering from PVS because patients may not show any other evidence of other meaningful response to the environment.

More difficulties with eye tracking may come into play because of the possibility of other neurological or ophthalmological damage that may prevent a patient from tracking stimuli. This means that a patient may actually have a degree of recovery that will be missed because it cannot be detected through eye tracking.
Emotional response is also difficult to determine because a response must be directly related to specific stimulus. This can be difficult because patients in PVS can scream, cry, grunt or have other actions associated with emotional responses, which are not done in response to stimuli. Therefore significant testing must be done to determine that emotional responses are not being done randomly, but are performed as responses.

A patient recovering from PVS usually recovers in a progressive manner where they move into a post vegetative state. Some patients have recovered significantly. Individuals with relatively short periods of time in PVS have been able to regain nearly normal physical and mental capabilities. There has also been documentation of individuals recovering from periods of PVS lasting over a year who have been able to regain the ability to think, communicate and recover a fair level of physical independence (move without a wheelchair, and feed themselves) (CRA 54).