Nervous System Could Be the Reason Behind Lingering Ocular Pain, New Study Finds

Nervous System Could Be the Reason Behind Lingering Ocular Pain, New Study Finds

November 19, 2021

The majority of the 16 million Americans diagnosed with dry eye each year get relief from artificial tears or prescription medicine, but some people continue to suffer from severe eye pain despite attempting a variety of therapies.

The solution, according to new research from the University of Miami, may lay in the way their nervous systems react to pain.

This information will aid researchers in developing more effective treatment techniques for a complicated disorder that appears to be influenced by a combination of biological, psychological, and social variables. The research was presented at the AAO 2021 conference.

Researchers used a technique called conditioned pain modulation (CPM) to evaluate how the nervous system reacts to pain in people with chronic eye pain.

People with a low CPM reaction feel pain more strongly than those who have a high CPM response. As a result, researchers believed that people with chronic eye pain, like people with other types of chronic pain, would have a low CPM response.

However, in a study of 296 patients, they discovered that those with chronic eye pain had a normal to high CPM response, implying that focusing on the nervous system may help improve treatments for this complex eye condition.

“This study adds to existing literature that shows abnormalities in the nervous system can contribute to painful dry eye symptoms, beyond direct damage on the surface of the eye,” said lead researcher Amy Huang, MD.

“Our hope for the future is that with more knowledge and information about the location of the abnormalities, more targeted therapies can be developed to relieve ocular pain symptoms in dry eye.”

What is Dry Eye Disease?

Dry eye disease is defined as a multifactorial disease of the tears and ocular surface that results in symptoms of discomfort, visual disturbance, and tear film instability with potential damage to the ocular surface.

It is accompanied by increased osmolarity of the tear film and subacute inflammation of the ocular surface.

The ocular surface (cornea, conjunctiva, accessory lacrimal glands), meibomian glands (specific sebaceous glands of the eyelid margin, which produce the outer lipid film of the tear film), the main lacrimal gland, and the innervation between them form a functional unit. Any or all of these structures may be affected in dry eye disease.

The Pathogenesis of Dry Eye Disease

Dry eye is a very complex disease. It is not just a question of lack of water and so it is impossible to treat patients just by lubricating the eye with water. It is a disease that involves a series of self-stimulating biological events, and the lack of tears, insufficient tear quality or their instability results in direct mechanical and/or osmotic stress, which causes further damage.

In addition, goblet cell loss results in further tear film instability or imbalance and thus, dryness. The drier the eyes become, the more inflammatory they become and the greater the inflammation, the more the eyes continue to dry out, i.e., a vicious cycle occurs.

To give more context on the vicious cycle theory, the dryness of the eye stimulates the nerves, the inflammatory reaction and inflammatory cells, and those act as stimulation for further damage, and so tears and their quality are reduced further, resulting in the disease becoming chronic.

Overall, the disease is very complex, with many risk factors, causes and aetiologies having been defined. As a result, it is difficult to resolve.