Dragging the image around with the mouse is simply not the best means of being sure you have investigated all of the image content when retouching. This is especially true if you are dealing with an abstract image or looking at a solid tone in a sky with no reference material. Whether you are looking for small dirt or moisture spots on your sensor or just distracting details there is a better and more methodical way to do this.
First, open your image and make the image at least full size (actual pixels), 100% on-screen. Depending on the image you may want to edit at 200%. Remember that at 100% on-screen your image is being shown to you about 3 times the size it will print given a 300 ppi resolution. The really small details may actually be invisible in the final print, or a reduced image for the web, but you will still want to do a thorough investigation. Editing at 100% guarantees that you will see all pixels in their reality.
Press the Home key and the image will automatically position itself so that the upper left corner is shown on the screen. The scroll bars may look slightly displaced as the canvas surrounding the actual image is still there. Move the scroll bars slightly to convince yourself of the image position. Now you can retouch anything in the first section of the image. When you are done press <Ctrl>[Cmd] Page Down and the image will move one section to the right. How many sections will be available will depend on your screen resolution and the image size and degree of enlargement.
When you finish the top “row” the Page Down key by itself will shift the image down one section. The <Ctrl>[Cmd] Page Up keys will move the image to the left one section at a time so you can move back across the second row. As the sections move there is a very small overlap so you will not miss any pixels for inspection. If you need to move in smaller increments to reveal a particular area such as a place where the pixels for editing run off an edge, simply add the Shift key to the mix and the sections will move 10 pixels at a time. Once you have edited the bottom row on-screen you are sure you have seen every pixel in the image.
This keyboard navigation is much more precise than the Navigator or scrolling with the mouse and you get used to it pretty quickly. The keyboard shortcut keys for moving the image within the window are as follows:
Home = Top Left / End = Bottom Right
Page Up = Move up one screen section / Page Down = Move down one screen section
Add <Cmd>[Ctrl] keys and Page Up moves left / Page Down moves right
Add the Shift key to the <Cmd>[Ctrl] key and the movement is limited to 10 pixels