I get eye fatigue pretty easily looking at my 24 inch computer screen (even when I had it set to low brightness), and this app does what I was hoping for. You can tweek how large you want the "spotlight" to be, and you can tweek how dark the background is too. I am currently using Mavericks, and this app has worked flawlesly for me. The only wish I have for this app would be if you could check off a setting that would allow the mouse pointer to disappear when the mouse has not been touched in several seconds. This kind of option would be really useful for watching youtube videos. This is probably soemthing that apple would have more control over than the makers of this app thought.