The answer to your question is not as easy as it may seem. There are a few things to consider:
1) Medicare uses different carriers to provide coverage to patients in different parts of the country. Each carrier has its own set of rules to determine whether or not you will meet their criteria. Just because you have extra skin in your eyelids doesn't mean Medicare will pay for your surgery.
2) Unlike some private insurers, Medicare does not preapprove surgery. Medicare relies on the doctor determining that you meet their criteria.
3) Medicare is in the middle of a nationwide, large scale audit on blepharoplasty surgery. This means they have hired independent contractors (RAC's) to go back and demanding records from doctors on surgeries that they performed several years ago. These RAC's get a financial incentive to determine that surgeries did not meet criteria (even if they did). If your surgery gets audited you may become financially responsible for your surgery years after the fact.
4) Even if your surgery is covered by Medicare, you will likely have a copay and may have to meet your deductible.
I know that was not a simple answer, but I hope it is helpful.