The cost of medical care for the nation's elderly has become much clearer over the past year, thanks to the public release of payments to doctors and hospitals from the federal Medicare program.

In Minnesota, Medicare's traditional program paid more than $811 million just for outpatient services in 2013, according to federal data released this week.

But the devil is in the small details of this big data. Journalists and health analysts used the 2012 figures released last spring to scrutinize physicians who receive the most money and to examine providers performing high rates of high-cost procedures.

Both years in Minnesota, the administration of costly Lucentis medication for macular degeneration made ophthalmology one of the most lucrative specialties. Eye specialists received more than $56 million from the program in 2013, making opthalmalogy the fourth most expensive specialty, behind internal medicine, family practice and diagnostic radiology.

Nine of 10 doctors who received the most money — at least $1.5 million each — from traditional Medicare in 2013 were ophthalmologists.

Payments for diagnostic radiology, such as CT scans, declined 7 percent, to $58 million. That could reflect Minnesota's sustained campaigns to reduce unnecessary testing.

The numbers draw a lot of scrutiny because Medicare is now the third-largest item in the federal budget, after Social Security and defense, and represents 20 percent of American health spending.

But limitations make the data hard to interpret. It doesn't include patients enrolled in managed-care plans instead of traditional Medicare, and it excludes payments to doctors who performed procedures on 10 or fewer patients.

Still, organizations such as Stratis Health can use the data to probe deeper into high-cost providers and specialties, said Stratis spokeswoman Deb McKinley. "It's a flag. It's enough to say there might be more to explore here … but in and of itself it isn't the full answer."