Protective shield... and why it was used?

In the pictures below, you can see a "factory new" glass filter for CRT screen. Such shields were used on nearly every new CRT screen in 1990, usually they were glued with stickers, hanged on special belts or mounted on Velcros. Why? There were a few reasons.
First, screens are made of glass. Glass reflects light and computer monitor screen reflects light even more because in most of DOS operation its surface remains dark. When user looks on screen, the contents should be shown, not reflections of the background. Cheaper plastic and more expensive glass filters minimized this effect.
Second, these filters at least tried to "flatten" the screen making eyes strain less. Although picture may be flat, looking at the non-flat surface of CRT may be the factor which makes eyes more tired with time.
But the main reason of purchasing shields was the fear of not-so-specified "radiation" coming from screens. Some people told that it was X-ray, but most of screens got rid of X-ray problems in 1980s. Other spoken about static electricity, and indeed this shield has conductive layer and grounding cable to drain the static electricity to ground. Another component of this urban legend were some unknown "microwaves" which came from the monitor and caused headaches. However, the biggest cause of headaches was always... using interlaced garphics modes :). So people bought these in a futile hope that these shields will make their problems smaller, and they usually made the brightness smaller. Similar accessories were "anti-ozone" devices for laser printers and (warning: huge urban legend) a pot with polypodium standing on TV or monitor.
In 1990s there was one more kind of special filter: Filters which made display's view angle smaller. Why make the view angle smaller? In many offices, a few displays were clogged on the same desk used by many people. These shields were used to make co-workers not lurk on your screen.