If you are using an external editor and do not access the external editor from iPhoto, the edits you make may not be reflected when viewing the image in iPhoto.
For best results, use iPhoto's built-in options for editing with an external editor.
Do not drag photos from the iPhoto window to the external editor's icon in the Finder or Dock. Instead, use iPhoto preferences to configure access to an external editor. This allows you to double-click or control-click an image in iPhoto to send it to the external application for editing.
See iPhoto help for more information on accessing an external editor from iPhoto.