Abstract
BackgroundAssessment of visual fixation is commonly used in the clinical examination of patients with disorders of consciousness. However, different international guidelines seem to disagree whether fixation is compatible with the diagnosis of the vegetative state (i.e., represents "automatic" subcortical processing) or is a sufficient sign of consciousness and higher order cortical processing.MethodsWe here studied cerebral metabolism in ten patients with chronic post-anoxic encephalopathy and 39 age-matched healthy controls. Five patients were in a vegetative state (without fixation) and five presented visual fixation but otherwise showed all criteria typical of the vegetative state. Patients were matched for age, etiology and time since insult and were followed by repeated Coma Recovery Scale-Revised (CRS-R) assessments for at least 1 year. Sustained visual fixation was considered as present when the eyes refixated a moving target for more than 2 seconds as defined by CRS-R criteria.ResultsPatients without fixation showed metabolic dysfunction in a widespread fronto-parietal cortical network (with only sparing of the brainstem and cerebellum) which was not different from the brain function seen in patients with visual fixation. Cortico-cortical functional connectivity with visual cortex showed no difference between both patient groups. Recovery rates did not differ between patients without or with fixation (none of the patients showed good outcome).ConclusionsOur findings suggest that sustained visual fixation in (non-traumatic) disorders of consciousness does not necessarily reflect consciousness and higher order cortical brain function.
Highlights
Assessment of visual fixation is commonly used in the clinical examination of patients with disorders of consciousness
Patients were assessed by means of the Coma Recovery Scale-Revised (CRS-R) [5] and showed the clinical criteria of VS as defined by the Multi Society Task Force on PVS [1]: (i) no evidence of awareness of self or environment and an inability to interact with others; (ii) no evidence of sustained, reproducible, purposeful, or voluntary behavioral responses to visual, auditory, tactile, or noxious stimuli; (iii) no evidence of language comprehension or expression; (iv) intermittent wakefulness manifested by the presence of sleep-wake cycles; (v) sufficiently preserved hypothalamic and brain-stem autonomic functions to permit survival with medical and nursing care; (vi) bowel and bladder incontinence; and (vii) variably preserved cranial-nerve reflexes and spinal reflexes
Five patients did not show visual fixation and five patients did - both groups were matched for age, etiology, time since insult and other clinical features
Summary
Assessment of visual fixation is commonly used in the clinical examination of patients with disorders of consciousness. Different international guidelines seem to disagree whether fixation is compatible with the diagnosis of the vegetative state (i.e., represents "automatic" subcortical processing) or is a sufficient sign of consciousness and higher order cortical processing. It is still a matter of debate whether visual fixation indicates "automatic" subcortical processing (i.e., is compatible with the diagnosis of the vegetative state; VS [1,2]) or whether it is a cognitively mediated behavior that heralds consciousness and higher order cortical processing (i.e., sufficient for the diagnosis of the minimallyconscious state; MCS [3]). UK guidelines state that "visual fixation of a target" is a "compatible but atypical feature"
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