Pain MeasurementPainPain, PostoperativeVisual Analog ScaleVisual CortexEvoked Potentials, VisualVisual PerceptionPain ManagementVisual AcuityVisual FieldsDouble-Blind MethodTreatment OutcomeVisual PathwaysLow Back PainChronic PainBack PainAnesthetics, LocalPain ThresholdAnalgesics, OpioidPain, IntractableProspective StudiesQuestionnairesNeck PainQuality of LifePain PerceptionSeverity of Illness IndexFacial PainAnalgesia, Patient-ControlledAnalgesics