Medicare Advantage plan enrollment increased to 11.8 million in April 2011, up 6% from the total recorded a year earlier, but some of the enrollees may have had a harder time reading their plan forms.

The percentage of Medicare Advantage program enrollees in plans that offer vision benefits seems to have fallen to 79%, from 84% in 2010, officials at the U.S. Government Accountability Office (GAO) report in a review of the Medicare Advantage program prepared at the request of Sen. Max Baucus, D-Mont., the chairman of the Senate Finance Committee, and Sen. Tom Harkin, the chairman of the Senate Health, Education, Labor and Pensions Committee.

The GAO researchers looked at bid pricing data and plan benefit package data from plans that cover about 71% of the Medicare Advantage program enrollees.

Medicare Advantage is a program that gives private insurers a chance to offer alternatives to traditional Medicare coverage.

The Patient Protection and Affordable Care Act of 2010 (PPACA) is supposed to impose funding changes that could cut into Medicare Advantage plan profits in 2012 and into availability of plans in 2013.

Earlier laws also have rattled program carriers, by, for example, requiring the carriers offering Medicare private fee-for-service (FFS) plans to include provider networks in the plan designs, in an effort to hold down overall use of medical services and medical costs.

The number of private FFS plans fell to 239 this year, from 435 a year earlier, and those plans suffered a 54% drop in totla enrollment, GAO investigators found.

But enrollment in health maintenance organization (HMO) plans, which account for the bulk of Medicare Advantage enrollment, increased 9%.

Enrollment in local Medicare Advantage preferred provider organization (PPO) plans increased 38%, and enrollment in regional Medicare Advantage PPO plans increased 58%.

The average monthly premium for an enrollee fell 14%, to $24.

Because PPACA now requires the plans to put limits on enrollees’ out-of-pocket expenses, 100% now do so, up from 74% in 2010.

The plans are about as likely to provide some types of optional benefits, such as health and education, this year as they were in 2010, but investigators found that the percentage offering extra skilled nursing facility benefits fell to 68%, from 72%.

The drop in coverage for vision benefits does not affect benefits for treatment of severe eye problems that have already been diagnoses, such as macular degeneration, but it does affect coverage for the kinds of routine eye exams that might detect those problems at an early stage. Medicare Advantage plan enrollees also have less access to coverage this year for buying contact lenses and eyeglasses.

“Such changes could be due to changes in plan offerings, changes in beneficiaries’ plan selections, or some combination of the two,” James Cosgrove, a GAO director, writes in a summary of the GAO’s findings.

The percentage of enrollees with extra hearing benefits, which might cover services such as hearing tests and products such as hearing aids, held steady at 64%.