The purpose of this research study is to test whether researchers can reliably measure the response pupils have when an acute painful stimulus is experienced. Changes in the size of the pupil of the eye can be an indicator of brain activity in a region of the brain that is important for feeling pain.

There is strong rationale to support a role for locus coeruleus (LC) responsivity to acute painful stimuli in regulating speed of recovery after surgery and for LC responsivity as a mechanistic link explaining the risks for slow recovery from weak Conditioned Pain Modulation (CPM), catastrophizing cognitive style, and low enzyme activity catecholamine-O-methyltransferase (COMT) genotype. Preliminary data show feasibility to perform the proposed study.

Primary Hypothesis: An observational study of pupil responses to noxious stimuli shows strong intra-individual reliability over 8 weeks.

Key secondary hypotheses: Compared to individuals homozygous for val at the val158met site of the catecholamine-O-methyltransferase (COMT) gene, those homozygous for met will show smaller pupil responses to noxious stimuli and weaker CPM.

Inclusion Criteria:

• Adult (18-70)
• Pain from hip or knee arthritis of moderate intensity
• American Society of Anesthesiologists physical status 1-3

Exclusion Criteria:

• Inability to complete study questionnaires
• Pregnancy
• Litigation or workers compensation related to hip or knee pain
• Taking > 50 mg morphine equivalents/day
• History of Raynaud's disease of the feet
• Psychotic disorder or a recent psychiatric hospitalization
• History of eye surgery or topical eye medications that would would directly affect pupil diameter

Individuals with athritis in the knee or hip with moderate average daily pain score