Mitt Romney may be the candidate, but Wednesday night, all eyes will be on running mate Paul Ryan at the Republican National Convention.

Specifically, people are listening for more on Ryan's controversial Medicare overhaul plan. But how exactly would the plan work, and who would it affect?

At senior centers, the talk is about Medicare, and changes that might be coming.

"I find it very scary, because I don't know what's going to happen," said Ann Kichline of Emmaus.

Democrats are pushing the issue hard. A new television ad claims, "Republicans want to end Medicare." The rhetoric has seniors, and others, nervous.

"Whoever wins, we're in trouble," said Anne Morris of Fountain Hill.

First, the facts: Americans are getting older and health care is getting more expensive.

"We develop new medicines," said George Nation, a health care industry expert at Lehigh University in Bethlehem. "We develop new, cutting-edge procedures, and they are very, very expensive."

How expensive? The Congressional Budget Office estimates Medicare spending will triple by the year 2050, to nearly 10 percent of the nation's Gross Domestic Product. Both Republicans and Democrats agree that spending must be reigned in, but they disagree on how.

Ryan's solution? Replace traditional Medicare coverage, which (like other HMOs) pays for any procedure that's covered, with vouchers. Those vouchers would have a set amount of money that seniors could spend on any procedure they want, but once the money runs out, the patient is responsible for the rest -- out-of-pocket.

"Every senior will get the same amount of money to spend on insurance, but depending on the insurance they select, that voucher may cover all of it or may not cover all of it," said Nation.

Seniors would be able to choose between Medicare and various private insurance providers in an "exchange." Whichever plan is the second-cheapest is the amount of money the government would provide in vouchers, according to Nation.

"What [Ryan is] hoping will happen, is that individials will demand lower prices from medical providers," he said. "Or another way to look at it is, demand more value."

Critics claim the plan will destroy Medicare as we know it.

"It's not going to be a way to get costs under control," said state Rep. Eugene DePasquale (D - York Co.), who is also running for Pennsylvania Auditor General. "Especially with seniors, their medical needs are so significant to begin with. I that they're at a stage of life where I don't think that model works."

Ryan's plan would not kick in for ten years, meaning no one over 55 is affected. Still, seniors used to making painful medical choices know more are coming.

"There are people who are going to be indignant and say, 'Well, we were promised this,'" said Morris. "Well, we've been promised a lot of things, and we don't always get what we're promised."

Democrats' fear is, if health care costs keep going up, seniors will get stuck paying more and more each year. Ryan is expected to address Medicare when speaks Wednesday night.