WASHINGTON, Jan 5 (Reuters) - The U.S. Food and Drug Administration and GlaxoSmithKline Plc (GSK.N: Quote, Profile, Research)(GSK.L: Quote, Profile, Research) have warned doctors about new or worsening eye complications in patients taking three of its diabetes drugs, according to a letter made public on Thursday. In most cases, patients taking rosiglitazone -- sold as Avandia, Avandamet and Avandaryl -- reported swelling of the eye known as macular edema, the company said in the letter sent last month. Such reports were "very rare," the letter said, but did not offer a figure. A company spokeswoman did not immediately return a call seeking comment. "In some cases, the macular edema resolved or improved following discontinuation of therapy and in one case, macular edema resolved after dose reduction," the letter said. Company officials said they proposed including a precaution in product information for doctors and in brochures for patients, according to the letter posted on the FDA's Web site at www.fda.gov/medwatch/safety/2006/safety06.htm#Avandia. Shares of Glaxo were off 3 cents at $51.92 in afternoon trading on the New York Stock Exchange after earlier closing up less than 1 percent in London.