Visits to the prison by outside physicians have become routine over the past few months. Joe Raedle/Getty Images

GUANTANAMO BAY, Cuba — The inmates of the detention center here were once considered the "worst of the worst" in the "war on terror." U.S. officials locked away hundreds of men picked up all over the world in a belief that they were all hardened enemies of America, ruthlessly committed to their cause.

But now, more than a decade later, many of the remaining detainees — the vast majority of whom have never been charged, and scores of whom have been cleared for release — are ailing as they get older behind bars. Their physical and mental health after years of captivity, often marked by hunger strikes, now requires frequent medical attention.

This week, an ophthalmologist was flown from the U.S. to the naval base to perform cataract surgery on two prisoners who have been held without trial for more than a decade. Navy Lt. Cmdr. William Greg, the officer in charge of the 15-bed detainee hospital, told Al Jazeera that visits to the prison by outside physicians have become routine over the past few months.

“As people age, there’s medical problems,” said Greg, a nurse who was deployed to Guantanamo two months ago. “For example, we just brought in a gastroenterologist to see our patients. We also just had a dermatologist here.”

There were no prisoners at the hospital when Al Jazeera toured the site. Greg said he does not see the most high-value prisoners — including Abu Zubaydah and Khalid Sheikh Mohammed, the self-professed mastermind of the 9/11 attacks — who are held in a top-secret camp at an undisclosed location on the base.

Greg said he is not authorized to disclose the identities of the prisoners undergoing surgery, because of privacy concerns. But he said he and the staff of the Joint Medical Group at the base have been treating prisoners who are battling problems ranging from obesity and diabetes to depression.

In fact, at least one prisoner has become so concerned with his diabetic condition that he requested the book “Diabetes for Dummies” from the detainee library, according to a library technician, Milton (who, like numerous other contractors who support the prison operations, would not disclose his surname for security reasons).