Fig. 2.

Design and study rationale. A Convenient bedside measures to detect residual consciousness in clinically unresponsive patients with acute brain injury are urgently required. B Notably, in states of unconsciousness, the sympathetic control of pupil size is thought to be lost. Instillation of brimonidine (an alpha-2-adrenergic agonist) eye drops in one eye should therefore produce miosis and anisocoria if clinically unresponsive patients are conscious (indicated by “lightning”), but not if they are unconscious. C In a first step to explore the usefulness of brimonidine eye drops to search for residual consciousness, we investigated the potential of brimonidine to distinguish preserved sympathetic pupillary function in awake volunteers from impairment of sympathetic tone in comatose patients in whom residual consciousness had been ruled out