OHSU researchers discover link between proteins in tears, pain after eye surgery

Researchers have discovered a connection between levels of specific proteins in patients' tears and persistent pain months after surgery such as LASIK. The discovery could help develop new screening tools and treatments. Results of the study, by scientists at Oregon Health & Science University (OHSU), published in the Journal of Proteome Research.

A patient's eyes and tears are tested in a cornea exam room in the Casey Eye Institute. Credit Christine Torres Hicks, OHSU.

Each year, more than 800,000 Americans undergo refractive surgery like LASIK and PRK to correct their vision. While these procedures generally have a high rate of success, a small number of people continue to feel pain or discomfort long after the surgery.

"A lot of people think tears are just salt water, when in fact we are able to detect thousands of proteins in human tears," said Sue Aicher, Ph.D., corresponding author on the study and a professor of chemical physiology and biochemistry in the OHSU School of Medicine who studies how cells function in neural circuits, particularly in pain.

The team recruited 120 study participants in Miami and Portland. None reported any eye pain before refractive surgery.

Three months after surgery, researchers took tear samples using a thin filter paper inserted beneath the lower eyelid to wick tears from the eye surface. This non-invasive procedure is used clinically for other diagnoses, such as assessing dry eye disease.

From the group of participants, 16 reported they still had pain. Researchers compared these participants' tears with those of the 104 participants who had no pain and identified 2,748 proteins in tears from both groups of participants.

When they compared protein profiles among the two groups, they found that some proteins differed in people who experienced long-term pain compared with those who did not. Additionally, researchers found patterns of protein differences mattered: Looking at three or four proteins together was better at predicting pain than a single protein.

"We hope to eventually develop drug treatments that modulate the proteins that are elevated, and see if that can treat the eye pain," Aicher said.