Evidence that dry eye is a comorbid pain condition in a U.S. veteran population

Introduction Recent evidence suggests that dry eye (DE) may be comorbid with other chronic pain conditions. Objectives To evaluate DE as a comorbid condition in the U.S. veteran population. Methods Retrospective review of veterans seen in the Veterans Administration Healthcare System (Veteran Affairs) between January 1, 2010, and December 31, 2014. Dry eye and nonocular pain disorders were ascertained by International Classification of Diseases, Ninth Revision (ICD-9) codes. Dry eye was further separated into ICD-9 codes representing tear film dysfunction or ocular pain. χ2 and logistic regression analyses were used to examine frequency and risk of DE, ocular pain, and tear film dysfunction by pain disorders. Results 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 < 0.0005). Ocular pain was most strongly associated with headache (odds ratio [OR] 2.98; 95% confidence interval [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. Conclusions Dry eye, including both ocular pain and tear film dysfunction, is comorbid with pain conditions in this nationwide population, implying common mechanisms.