Medicare Advantage plans are private health plans, such as HMOs or PPOs, that are offered by health insurers that have contracts with the Medicare program to offer benefits to people with Medicare. The plans provide all Medicare-covered benefits under Parts A and B, and usually provide Part D prescription drug benefits as well. Most Medicare Advantage plans also provide benefits that are not covered under traditional Medicare, such as eyeglasses, some dental care, or gym memberships. The plans also have a limit on out-of-pocket spending for services covered under Parts A and B, and may have lower cost-sharing than traditional Medicare for Medicare-covered services. However, Medicare Advantage plans restrict the health care providers that their enrollees can see (provider networks) whereas beneficiaries in traditional Medicare can see any doctor that accepts Medicare, without needing prior authorization or a referral from their primary care doctor.