A screen magnifier is software that interfaces with a computer's graphical output to present enlarged screen content. By enlarging part (or all) of a screen, people with visual impairments can better see words and images. This type of assistive technology is useful for people with some functional vision; people with visual impairments and little or no functional vision usually use a screen reader.
The simplest form of magnification presents an enlarged portion of the original screen content, the 'focus', so that it covers some or all of the full screen. This enlarged portion should include the content of interest to the user and the pointer or cursor, also suitably enlarged. As the user moves the pointer or cursor the screen magnifier should track with it and show the new enlarged portion. If this tracking is jerky or flickers it is likely to disturb the user. Also, the pointer or cursor may not be the content of interest: for example, if the user presses a keyboard shortcuts that opens a menu, the magnified portion should jump to that menu. Pop-up windows and changes in system status can also trigger this rapid shifting.
Screen magnifiers can be especially helpful for people suffering from low vision, including elderly users. However, in a 2001 paper, Vicki Hanson noted that people with low vision often also suffer from additional disabilities such as tremors.
Ranges of 1- to 16-times magnification are common. The greater the magnification the smaller the proportion of the original screen content that can be viewed, so users will tend to use the lowest magnification they can manage.
Screen magnifiers commonly provide several other features for people with particular sight difficulties:
If the Magnify command was not assigned to a button on your mouse by default, you can assign it to one. [...] To turn on or turn off the Magnifier[:] Click the mouse button assigned to Magnify.