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Accommodation: The focusing of the lens of the eye in response to the distance of an object from the observer.

Acquired brain disorder: Any pathological process that causes damage to the brain resulting in neuropsychological impairment.

Anosmia: Loss of the sense of smell.

Ataxia: The inability to coordinate the muscles in the execution of a voluntary movement.

Attention: A concept that captures many different aspects of cognition, including the ability to focus for short or long periods on a single stimulus and the ability to attend to multiple pieces of information simultaneously.

Babinski's sign (Babinski reflex, Babinski's phenomenon): Extension of the great toe and abduction of the other toes instead of the normal flexion reflex to plantar stimulation; considered indicative of pyramidal tract involvement.

Central field of view: The portion of the field of view seen by the macula.

Clonus: A form of movement marked by contractions and relaxations of a muscle that occur in rapid succession.

Confusion: A mental state in which reactions to environmental stimuli are inappropriate because the subject is disoriented or behaves in an unpredictable or unexpected manner.

Contralateral: Relating to or describing the opposite side.

Contrast sensitivity: The ability of the eye to detect various shades of gray or color shades.

Convergence: The direction of the visual lines to a near point.

Coordination: The organized functioning of muscles and muscle groups directed towards purposeful and controlled movement patterns.

Diplopia (double vision): A disorder in which a single object is perceived as two objects.

Divergence: The direction of the visual lines to a far point.

Dizziness: An imprecise term used to describe faintness, a sense of disorientation, physical unsteadiness, vertigo, or disequilibrium.