Some of the risk factors in this study are typical (sleep apnea, because they're probably all using CPAP which is blowing in their eyes; thyroid disease has a known connection) but I find the connection with depression and PTSD quite interesting - I wonder if that really is as simple as antidepressant, antianxiety etc side effects or there is more to it. I tend to think that those conditions enhance eye pain in individuals who are not on medication.
Prevalence and Risk Factors of Dry Eye Syndrome in a United States Veterans Affairs Population.

PURPOSE:
To evaluate the prevalence of dry eye syndrome (DES) and its associated risk factors in a US Veterans Affairs population receiving ocular care services.

DESIGN:
Retrospective study.

METHODS:
settings: Patients were seen in the Miami and Broward Veterans Affairs eye clinics between 2005 and 2010. patients population: Patients were divided into cases and controls with regard to their dry eye status (cases = ICD9 code for DES plus dry eye therapy; controls = patients without ICD9 code plus no therapy). Main outcome measures: The prevalence of DES and its associated risk factors.

RESULTS:
A total of 16 862 patients were identified as either a dry eye case (n = 2056) or control (n = 14 806). Overall, 12% of male and 22% of female patients had a diagnosis of DES, with female gender imparting a 2.40 increased risk (95% confidence interval [CI] 2.04-2.81) over male gender. Several medical conditions were found to increase DES risk including post-traumatic stress disorder (odds ratio [OR] 1.97, 95% CI 1.75-2.23), depression (OR 1.91, 95% CI 1.73-2.10), thyroid disease (OR 1.81, 95% CI 1.46-2.26), and sleep apnea (OR 2.20, 95% CI 1.97-2.46) (all analyses adjusted for gender and age). The use of several systemic medications, including anti-depressant medications (OR 1.97, 95% CI 1.79-2.17), anti-anxiety medication (OR 1.74, 95% CI 1.58-1.91), and anti-benign prostatic hyperplasia medications (OR 1.68, 95% CI 1.51-1.86), was likewise associated with an increased risk of DES.

CONCLUSIONS:
The prevalence of DES was found to be high in both men and women in our eye care population. This is the first study to demonstrate that in a veteran population, several diagnoses were significantly associated with DES, including post-traumatic stress disorder and depression.
Am J Ophthalmol. 2011 Jun 17. [Epub ahead of print]
Galor A, Feuer W, Lee DJ, Florez H, Carter D, Pouyeh B, Prunty WJ, Perez VL.
Source
Bascom Palmer Eye Institute, University of Miami, Miami, Florida; Miami Veterans Administration Medical Center, Miami, Florida.