An official website of the United States government
The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before
sharing sensitive information, make sure you’re on a federal
government site.
The site is secure.
The https:// ensures that you are connecting to the
official website and that any information you provide is encrypted
and transmitted securely.
López-Moliner J, Field DT, Wann JP.López-Moliner J, et al.J Vis. 2007 Oct 29;7(13):11.1-8. doi: 10.1167/7.13.11.J Vis. 2007.PMID: 17997639Free article.