Eye color linked to pain tolerance in pilot study at Pitt

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Pain comes in all shapes and sizes. Whether it arises in the chronic form of arthritis or the sudden squeeze of cardiac arrest, pain is the main motivator for a visit to the hospital.

Doctors may now have to note the eye color of their patients before choosing a procedure to treat them. New research has shown that women with dark -- brown and hazel -- eyes respond differently to pain than those with light -- blue and green -- eyes.

During the 2014 annual meeting of the American Pain Society, Inna Belfer, M.D., Ph.D., an associate professor of anesthesiology at the University of Pittsburgh, presented a study possibly linking eye color to variations in pain tolerance.

The study sample consisted of 58 healthy pregnant women at Magee-Womens Hospital of UPMC. Twenty-four women were placed in the dark group, and the remaining 34 were placed in the light group. Dr. Belfer and her team measured responses to pain before and after giving birth through a variety of quantitative standard testing, questionnaires, and surveys.

The results indicated that women in the dark group experienced more dramatic response to pain with increases in anxiety and sleep disturbances than those in the light group.

“This was a small pilot study to start off,” said Dr. Belfer. “All we know now is super limited -- a hypothesis about why there is a difference at this point would be too optimistic -- but this could be a next step in finding a genetic background of pain.”

Identifying eye color as a genetic biomarker for pain thresholds will be advantageous for the medical community.

“Right now we don't know who is going to feel more severe pain after standard surgery or develop chronic pain,” said Dr. Belfer, “This is a problem for both patients who are suffering and society."

Determining a visible indicator of a genetic signature that predicts pain tolerance will "help to identify those targeted patients, and the earlier you can identify them, you will be in better shape for the future.”

This is not the first research that has related phenotypic differences and pain. Multiple studies have correlated red hair to resistance to pain blockers and requirements for higher doses of anesthesia. Dr. Belfer and her team also discovered three studies that link eye color to physiological activity.

Dr. Belfer plans to continue the research on this topic by expanding to studies including men, children and larger, more comprehensive distinctions between groups.


Campbell North: cnorth@post-gazette.com or 412-263-1613.

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