BAKERSFIELD, Calif. -- It's a good time to be an optometrist -- new research has found that more Americans need corrective lenses to improve their vision.

An analysis from the National Eye Institute revealed a sharp increase nearsightedness, or myopia, over the last 30 years. The most recent data show nearly 42 percent of Americans ages 12 to 54 are nearsighted -- compared to just 25 percent from the early 1970s.

And we're not alone: studies from Asia, Australia and Sweden have found similar trends.

Why the sudden increase? Scientists have multiple theories. Some said there are more people now with genetic susceptibility to myopia. Others blamed the spread of computer technology -- perhaps the long hours of close-up work are changing the shape of our eyeballs.

Nearsightedness is a problem that is easily corrected with glasses, contacts or even laser surgery. But researchers said people may not want to see the collective costs of poor vision -- they calculated the added cases of myopia total an extra $3 billion in medical bills.