While retirees are optimistic about their retirement, olderworkers who haven't yet left the workplace, and women between theages of 50–65, aren't quite so cheery.

Read: Confidence in retirement readiness–what'sthat?

That's according to a survey from American Funds, which foundthat there was surprising optimism among U.S. adults age 50 yearsor older who have at least $100,000 in investable assets and someresponsibility for making investment decisions for theirfamily.

Nearly nine out of every 10, the survey found, expect their nestegg to generate income and grow in retirement.

Considering Americans' worries about how to make theirretirement savings last all through retirement, that's anunexpectedly large number—but 23 percent of those respondents hadmore than $1 million in investable assets, and 31 percent hadbetween $500,000–$1 million.

Forty-two percent of those with more than $1 million in assetsstrongly agree their nest egg will grow in retirement, while thosewith fewer assets aren't as convinced.

Read: 10 questions to ask about retirementpreparedness

Among those with assets between $100,000–$1 million, only 32percent expect that nest egg to grow once they retire.

Seventy-four percent believe a well-designed portfolio can dobetter than the market and do better than average. However, blindspots may leave them exposed to unexpected losses.

Although 78 percent of respondents say that protecting theirsavings from market downturns is a key priority, and believe thatlower volatility and downside resilience are important for theirmutual funds, only 53 percent of respondents realize that indexfunds expose investors to the full ups and downs of the market.

And just about a third agree that index funds are potentiallyriskier for investors who have less time to build their savings orrecover from a downturn.

Among respondents still in the workplace, only half expect tohave more retirement income than their parents did.

And women under 65 are among those most concerned aboutprotecting their retirement savings from market downturns.