It is generally recognized that pain assessment and management especially in newborns, children and other nonverbal populations is an unmet need. According to the American Medical Association, "the pediatric population is at risk of inadequate pain management, with age-related factors affecting pain management in children. Children are often given minimal or no analgesia for procedures that would routinely be treated aggressively in adults. Although much is now known about pain management in children, it has not been widely or effectively translated into routine clinical practice". These two factors combine to emphasize the necessity for an objective tool to quantify pain and monitor the effectiveness of analgesia, especially during treatments. Further, it is reported that many patients require a combination of treatments, and it is often necessary to test a variety of treatments before the personal match for treatment is found. The method in place to change the care on a subjective basis is difficult, time consuming, and not easily individualized. This pilot study is part of an ongoing effort to develop a method to objectively assess response to specific analgesic interventions. It specifically aims to discern the impact of analgesic interventions on sensory nerve fiber sensitivity in a diverse patient population.

Inclusion Criteria:

1. The subject is 7 to 21 years of age
2. The subject is receiving an analgesic intervention in the Children's National Medical Center Pain Clinic
3. The subject is willing and able to provide written informed assent/parental consent to the study participation.

Exclusion Criteria:

1. Eye pathology precluding pupillometry
2. Patients who are actively using opioids (history of use acceptable). Rationale: opioids constrict the pupil, and therefore concomitant opioid use would bias our results.
3. Subjects who are or may be pregnant

Patients who are receiving pharmacological or non-pharmacological analgesic interventions as part of their regularly occurring clinical treatment.