Why are Inverted Colors considered an accessibility feature?

Why is it that in most Operating Systems the "Inverted Colors" display setting is considered an accessibility feature? Both Windows and OS X includes this option so it seems to be a recognized feature, not a vendor specific quirk.

I understand that some users are color-blind. This would justify the Black & White, or grey-scale modes. What I don't understand is how or why does inverting the display color help someone with any specific, visual impairment or dysfunction.

As a programmer that wants to understand the need so that I can develop better, accessible software, what purpose does this feature serve to the end user who has some form of visual impairment?


UPDATE

I asked this question quite a while ago, however, it just dawned on me-- I think I am one of those individuals that this feature was designed for. I almost always try to keep the contrast reversed from the typical settings for my text displays. I hate white backgrounds with dark text! As a coder, all of my textual GUIs are black with green text. This isn't just a throwback to the old monochrome, green screen days. The pairing of the two colors is quite comfortable to my eyes. However, stairing at to much black-on-white actually hurts my eyes from some form of eye strain.

I mention this in an update because the color inversion feature is not useful.. it's annoying! As someone who needs a good feature like this, it's a shame that all implementations that I have ever seen are just a poor attempt at solving a problem. I would hope that Apple, Microsoft and others have done their research but I'm guessing that's not the case. This was probably an ill-thought of feature 10+ years ago, and they just continue to provide so their is no loss of functionality.

Developers, if you want to help people who need such a feature as to prevent eye-strain, find ways to change the text and page background, not the entire display! It just looks hideous and is just as offensive to the eyes. Especially when you tend to set background images on your display to darker colors. You can invert the coloring in word processors, text boxes and other text based devices.

If you really wanted to get creative, find a way to lightly color correct images, rather than inverting them. Decrease the contrast or decrease the brightness of images in a very subtle manner.