Many U.S. veterans who have traumatic brain injury or post-traumatic stress disorder also have undiagnosed, chronic vision problems, according to two new studies.

The research was presented Sunday at the 116th Annual Meeting of the American Academy of Ophthalmology in Chicago.

In a study conducted at the Veterans Affairs Medical Center in Washington, D.C., researchers found that vision problems in veterans with mild TBI are much more common and persistent than previously recognized. Though none of the affected veterans had suffered direct eye wounds, their vision continued to be impaired more than a year after they endured the injuries that caused their TBI.

The vision problems most frequently reported were the ability to focus both eyes simultaneously in order to read or see other nearby objects, sensitivity to light, readjusting their focus when moving their gaze between far and near objects and double vision.

"Physicians who care for veterans with TBI need to know that many of them have vision problems," Dr. M. Teresa Magone, who led the study, said in a statement. "It is critical that these patients receive vision assessment and when appropriate, be referred to ophthalmologists to make sure they get the eye care they need, for as long as they need it."

Another study of veterans conducted at the University of Miami found that those who have post-traumatic stress disorder (PTSD) or depression are more likely to develop dry eye syndrome than veterans who do not have these psychological diagnoses.

In their review of more than two million veterans' medical records, the research team found that about 20% of those diagnosed with PTSD or depression have dry eye syndrome, a disorder that disrupts the tear glands' ability to keep the eyes moist.

"Many vets won't mention that their eyes always feel gritty or seem to water for no reason, unless they're asked," said Dr. Anat Galor, who led the second study. "Since dry eye can escalate and permanently damage vision if untreated, it's crucial that health professionals who care for veterans with psychiatric diagnoses ask them about specific dry eye symptoms and refer them to an ophthalmologist if needed."