Novartis AG, Europe's biggest drugmaker by sales, said its Alcon eye-care unit is under U.S. government investigation related to the export of products to Iran and other countries subject to trade sanctions.Alcon was notified last year that the U.S. attorney's office for the Northern District of Texas is conducting an investigation into its sales, Novartis said in a regulatory filing Wednesday. Alcon, whose U.S. headquarters is in Fort Worth, received a grand jury subpoena for documents dating to 2005, according to the filing with the Securities and Exchange Commission.The U.S. attorney's office was not available for comment.Alcon, which employs more than 2,500 people in Fort Worth, is cooperating with the investigation, its filing said. The U.S. government has programs that prohibit or limit products made or held in the U.S. from being sold to certain countries, including Iran, Syria and North Korea.Novartis, based in Basel, Switzerland, took full control of Alcon in 2010.Also Wednesday, Novartis Chairman Daniel Vasella, who oversaw the 1996 merger of Sandoz AG and Ciba-Geigy AG, which created Novartis, unexpectedly said he will leave after 17 years. Joerg Reinhardt, now Bayer AG's top healthcare executive and a Novartis executive until 2010, will replace Vasella as chairman.The choice of Reinhardt, 56, puts another veteran pharmaceutical executive at the head of Novartis' board as the company navigates patent expirations on some of its top-selling medicines. Novartis forecast a mid-single-digit percent decline in profit this year and sales in line with 2012.Staff writer Sandra Baker contributed to this report.