More than 200,000 eyelid lifts were performed in the U.S. last year. (Media for Medical/UIG/Getty Images)

Drooping eyelids may seem like an inevitable effect of getting older, but sagging eyelids not only age a person's face, they can impair peripheral vision too.

Removing the excess skin through surgery can both improve vision and result in a more youthful appearance, but determining whether the procedure is cosmetic or medically necessary has become a point of controversy, especially since Medicare is increasingly picking up the tab.

An article from the Center of Public Integrity, a nonprofit investigative news organization, found that Medicare paid the bill for 156,000 eyelid lifts in 2011, a threefold increase since 2001. But the American Society of Plastic Surgeons said this increase did not coincide with an increase in the total number of eyelid lifts in the United States, which from 2000 to 2012 actually decreased by 38 percent, from 327,514 in 2000 to 204,015 in 2012.

The increase in eye lift surgeries covered by Medicare has also risen disproportionately to the number of people on Medicare. In 2010 there were 47.5 million people enrolled in Medicare, up from 39.7 million in 2000, an increase of about 20 percent, according to the U.S. Census Bureau.

Eyelid lifts, called blepharoplasties, are done when the upper eyelid, which usually hangs about 2mm above the pupil, starts to sag. It can be removed for cosmetic reasons or because it starts to block a person's peripheral vision.

According to the Center of Public Integrity, Medicare pays $574 to $640 per eye. Dr. Michael Migliori, president of the American Society of Ophthalmic Plastic and Reconstructive Surgery, estimates that the cost of a blepharoplasty is often about four to five times that rate, although he cautions that's only an estimate.

According to the American Society of Plastic Surgeons, the average surgeon's fee for the operation was $2,972 in 2012.

Dr. Mami Iwamoto, a Boston-based ophthalmologist who performed a blepharoplasty on Boston Mayor Tom Menino last year, said she has to say no to some patients who think they need a functional blepharoplasty - one that would improve their vision - but who don't meet the medical criteria.

"We're the final word on it," said Iwamoto. " She said she'll tell them, "'It's not medically necessary.' In their hearts they know that."

There are no national Medicare criteria for what determines a functional blepharoplasty. Different Medicare contractors that cover different regions of the country have their own criteria, although Migliori said that the criteria were fairly uniform across the country.

For Medicare to cover the surgery, according to Migliori and the Centers for Medicare and Medicaid Services, a doctor must perform two vision tests, which measure the degrees to which a person can see peripherally from the horizon. The surgery would have to theoretically improve a patient's peripheral vision by a specific number of degrees to be approved. The number of degrees depends on what is required by the individual Medicare contractor.

Other private insurance companies often use the same criteria as Medicare to determine if an eye lift is necessary, according to Migliori. United Health Group, one of the largest private U.S. health insurance carriers, uses the Medicare guidelines to determine if a blepharoplasty is medically necessary or if it is cosmetic.

According to Migliori, a photo of the patient also has to be included to show that he or she has sagging eyelids, and the patient must report additional symptoms, such as headaches from straining their eyebrows or injuries from running into things they can't see. Migliori said one common early sign was difficulty reading.

At the end of the day, the eyelids might become so heavy they can't open them, said Migliori, "even though they're not tired."

Dr. Robert Benson, a commissioner at the Medicare Payment Advisory Commission and a fellow at the Urban Institute, said the rise in Medicare-covered eyelid lifts was worrying because the difference between what makes an operation medically necessary or simply cosmetic is so minor.

"There's some clear-cut cases where eyelids interfere with vision, but a few doctors say everybody at age 70 or 80 has it, which I'm skeptical about it," said Benson. "This is a tough one, because in most of these things, you've got this objective criteria … but the subjective stuff may be the most important."

When reached for comment, a spokesman at the Center for Medicaid and Medicare Services said it had systems in place to root out fraud, including the ability to screen medical bills and to review medical practices that have had suspicious billing.

"The Center for Medicaid and Medicare Services takes seriously allegations of any abuse of Medicare benefits, and we have in place a series of tools to spot and stop fraud," the center said in a statement. "We believe these tools, including sophisticated data analytics and stronger enrollment and screening requirements for health care providers, made possible by provisions of the Affordable Care Act, will protect the Medicare Trust Fund."

Migliori said that one reason for the tremendous increase in the number of eyelifts covered by Medicare could be the number of uninsured or underinsured patients who wait until their Medicare coverage kicks in to get the surgery.

"There are a number of people who wait until they're Medicare eligible," said Migliori. "Their insurance may be better. Blepharoplasty is a legitimate problem."

Migliori also said that the surgery was more likely to be needed by older people, who are the ones covered by Medicare.

"It's not a life-threatening condition, [but] for older folks it's a safety thing," said Migliori. "We don't do a lot of functional blepharoplasties on people in their40s or 50s.