If an OD sees a lot of dry eye patients or has relatives with chronic pain, she may be familiar with how people feel pain differently. I am fortunate enough to be in both situations.
I see a large number of dry eye patients, most with significant chronic pain complaints. These patients often suffer from pain that is out of proportion to the clinical signs. Common treatments often to do not relieve their symptoms, leaving us both frustrated.
My view on these patients is certainly colored by experiences with chronic pain in my family. I have a child with hypermobility joint syndrome (HJS) (think Ehlers-Danlos syndrome [EHS]) who has been dealing with chronic pain since 2013. It is extremely difficult to undergo tests, scans, scopes, surgeries, and countless doctor’s visits, only to be told nothing can be found.
It took five years for a proper diagnosis—primarily because our specialists narrowed their wheelhouse so much that they could not see the forest through their own set of trees.
Previously by Dr. Swartz: Blog: A parent's perspective on genetic testing
I was educated about pain gate by a rheumatologist. The Gate Control Theory of Pain is credited to psychologist Ronald Melzack and biologist Patrick Wall in 1965.1 Since that time, the Gate Control Theory was modified in 1978 and 1996.2,3 Even as knowledge of the nervous system developed, the theory has remained consistent.4,5
According to this theory, pain messages travel from peripheral nerves to nerve “gates” located in the spinal cord and continuing to the brain. These central nervous system “gates” describe how some pain messages are allowed to continue to the brain while others are blocked.
In addition to controlling pain message “traffic,” the gates can also amplify or diminish pain signals. According to this theory, patients who suffer more pain have more open gates. Those who suffer less pain have fewer open gates.
Acute and chronic
In order to understand this theory, it is necessary to understand the difference between acute and chronic pain.
Fast pain signals use A-delta fibers. These are crucial to protecting the body from injury, such as removing one’s hand from a hot plate. This may be referred to as “warning pain.” A-delta signals do not last long and are delivered to the brain’s sensory cortex.
Chronic pain messages move more slowly along C-fibers, and these signals last longer. This pain may be described as nagging, aching, dull, or burning—this may be referred to as “reminder pain.”
These signals may be responsible for reminding the brain that it has suffered an injury.
Unfortunately, chronic pain may continue after the injury heals. The signals are delivered to the hypothalamus and the limbic system to release stress hormones and handle emotions. Thus, stress, depression, and anxiety are associated with chronic pain.
1. Melzack R, Wall PD. Pain mechanisms: a new theory. Science. 1965 Nov 19;150(3699):971-9.
2. Wall PD. The gate control theory of pain mechanisms. A re-examination and re-statement. Brain. 1978 Mar;101(1):1-18.
3. Melzack R. Gate control theory: On the evolution of pain concepts. Pain Forum. 1996 Summer; 5, 128-138.
4. Dickenson AH. Gate control theory of pain stands the test of time. Br J Anaesth. 2002 Jun;88(6):755-7.
5. Mendell LM. Constructing and deconstructing the gate theory of pain. Pain. 2014 Feb;155(2):210-6.
6. Zampino C, Ficacci R. Pain Control by Proprioceptive and Exteroceptive Stimulation at the Trigeminal Level. Front Physiol. 2018 Aug 7;9:1037.
7. Deogaonkar M, Slavin KV. Peripheral nerve/field stimulation for neuropathic pain. Neurosurg Clin N Am. 2014 Jan;25(1):1-10.
8. Vickers AJ, Vertosick EA. Acupuncture for chronic Pain: Update of an individual patient data meta-analysis. J Pain. 2018 May;19(5):455-474.
9. Kaur T, Shyu BC. Melatonin: A New-Generation Therapy for Reducing Chronic Pain and Improving Sleep Disorder-Related Pain. Adv Exp Med Biol. 2018;1099:229-251.
10. Khouzam HR. Psychopharmacology of chronic pain: a focus on antidepressants and atypical antipsychotics. Postgrad Med. 2016;128(3):323-30.