Poor eyesight may be affecting the productivity of as many as 40% of U.S. office workers.

Researchers at WellPoint Inc., Indianapolis, have reported that finding in a summary of results from a recent survey of 1,000 U.S. workers ages 18 and older.

More than a quarter of the survey participants who are office workers said they are getting headaches from trying to read small font sizes on display screens at work, and 11% said they have sent e-mails to the wrong people because they could not read the displays on their cell phones properly.

About one-third of the participating office workers said they had not seen an eye doctor because of the expense, or because of a lack of vision care coverage.