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Eye Color a Potential Cue to Pain Tolerance…

Physicians often flag patients with red hair, given its understood role as a biomarker for resistance to anesthetics; now, new research suggests that eye color may indicate how individuals will respond to pain as well.

According to the results of a recent study involving 58 pregnant, white women—24 with dark-colored eyes (brown or hazel) and 34 with light-colored eyes (blue or green)—individuals with darker eyes showed increased anxiety (P=0.01), and trended toward increased sleep disturbance (P=0.19) and less improvement in catastrophizing/rumination (P=0.15) compared with their lighter-eyed counterparts. Those with darker eyes also showed trends toward experiencing more pain both at rest (P=0.28) and during movement (P=0.22) after receiving epidural analgesia.

Inna Belfer, MD, PhD, associate professor in the Departments of Anesthesiology & Human Genetics and director of the Molecular Epidemiology of Pain Program at the University of Pittsburgh School of Medicine, presented the findings at the American Pain Society 33rd annual scientific meeting in Tampa, Fla. (poster 197).

“Human pain is correlated with many factors such as gender, age and even hair color,” Dr. Belfer said. “If we can prove that eye color is another genetic biomarker, it would be great because that’s exactly what we are looking for. Biomarkers can be instantly recognized, aren’t invasive and can save time and money. We are constructing a pain genome and are figuring out how it can be used in the future, so basically the more we know the better it will make the treatment process.”

To measure their response to pain, the women were assessed by using standard validated tools, including the Brief Pain Inventory, the Patient-Reported Outcomes Measurement Information System anxiety/depression/sleep scales, the Pain Catastrophizing Scale and Quantitative Sensory Testing.

Dr. Belfer noted that although these distinctions in pain reduction indicate a trend, they are not clinically significant. The next step, she said, is to conduct a study with a large sample size that will encompass many patient populations.

“I want to examine the eye colors individually because color is all about genes, and therefore a clear distinction between them is important,” she said. “We also want to look at the relationship between eye color and pain in different races, in nonpregnant women and in men. Dentists are super cautious when they have patients with red hair, so there’s no reason why, if the correlation exists, that eye color can’t be another thing to look out for as well.”

—Paul Bufano