Noah Fisher is a shy four year old who was prescribed glasses. His mom, Lindsay, created a Facebook page called “Glasses for Noah” and asked people to upload photos of them wearing glasses so that he would not be shy about it. The response has been overwhelming.
That's quite simple, you just need to remove the polarized layer from your computer screen and use new polarized sheets to make polarized glasses out of 3D glasses for example.
Only the person wearing the special glasses can see what's on screen, others will just see a blank monitor.
Better try that first on a used monitor you don't care about though...