Researchers Find Veterans Suffer From Dry Eye As a Comorbid Pain Condition

Dry eye (DE) was found to be a comorbid pain condition among US veterans, raising the suggestion that pain specialists screen for this disorder in their chronic pain patients, researchers reported recently.

Researchers performed a retrospective review of veterans seen in the Veterans Administration Healthcare System (Veteran Affairs) between January 1, 2010, and the end of 2014. DE and nonocular pain disorders were determined by International Classification of Diseases, Ninth Revision (ICD-9) codes.

This study, published in Pain Reports, examined the frequency and risk of DE, ocular pain, and tear film dysfunction by pain disorders. DE, which can present as ocular pain and/or tear film dysfunction, affects an estimated 15% of the US population.

Symptoms of DE include a wide range of unpleasant sensations, including “dryness,” “burning,” and “aching." Signs can include decreased tear production, increased tear evaporation, and ocular surface disruption. DE symptoms often do not correlate with clinical signs of DE, and a subset of patients do not respond to therapies that target the ocular surface.

Patients with DE symptoms report a negative impact on their quality of life due to difficulties with daily activities such as reading, watching television, driving, and using a computer.

Chronic pain conditions (typically lasting 3 months or longer) are estimated to affect at least 116 million US adults and cause an estimated economic burden of $560—$635 billion in medical spending because of treatment costs and loss of productivity.

Certain chronic pain conditions, such as temporomandibular joint dysfunction (TMD), fibromyalgia, irritable bowel syndrome, back pain, and headaches, have been found to coexist with one another, and this concept has been referred to as chronic overlapping pain conditions (COPCs).

COPCs are further separated into categories based on the presence or absence of observable underlying disease. “Functional disorders” describe conditions where pain exists without known underlying pathology (eg, TMD, fibromyalgia). Structural disorders occur in the setting of a well-defined pathology (eg, osteoarthritis, rheumatoid arthritis), infection (eg, postherpetic neuralgia), drug-induced (eg, opioids), or trauma (eg, persistent postoperative pain).

Several mechanisms common to COPC are implicated in the pathogenesis of chronic DE symptoms, including inflammation, nerve sensitization, and genetic susceptibility. Similar to COPC, psychosocial vulnerabilities likely play a role in ocular symptom amplification, as demonstrated by the close association between DE with posttraumatic stress disorder, depression, and insomnia.

Researchers of the current study evaluated the association between DE subtypes (including ocular pain and tear film dysfunction) with nonocular pain conditions listed under the heading of COPC in a nationwide sample of veterans.

They hypothesized that DE, specifically the subtype defined by ocular pain, would be more prevalent in individuals with pain conditions with functional conditions known to associate with central sensitization, compared with individuals with a reported diagnosis of DE with tear film dysfunction.

Of 3,265,894 veterans, 959,881 had a DE diagnosis (29.4%).

Dry eye frequency increased with the number of pain conditions reported (P <.0005).

Ocular pain was most strongly associated with headache (OR 2.98; 95% CI 2.95—3.01), tension headache (OR 2.64; 95% CI 2.58–2.71), migraine (OR 2.58; 95% CI 2.54–2.61), temporomandibular joint dysfunction (OR 2.39; 95% CI 2.34–2.44), pelvic pain (OR 2.30; 95% CI 2.24–2.37), central pain syndrome (OR 2.24; 95% CI 1.94–2.60), and fibromyalgia/muscle pain (OR 2.23; 95% CI 2.20–2.26), all P < 0.0005.

Tear film dysfunction was most closely associated with osteoarthritis (OR 1.97; 95% CI 1.96—1.98) and postherpetic neuralgia (OR 1.95; 95% CI 1.90–2.00), both P < 0.0005.

The researchers said the results support the idea that DE (both ocular pain and tear film dysfunction) is comorbid with pain conditions in this nationwide population, implying common mechanisms.

Reference

Lee CJ, Levitt RC, Felix, ER, et al. Evidence that dry eye is a comorbid pain condition in a U.S. veteran population. Pain Rep. 2017;2(6):e629-e637. doi: 10.1097/PR9.0000000000000629.