So in the list of specifically illegal equipment in the Fed rules, spectacle guards makes an appearance. The trouble is, I have no idea what they are. Also, no one I have ever put the question to know what they are. So, what are they?
Have no idea, but on ancient helmets, it was an extra panel protruding down from the lower rim of the front of the helmet that included two eye cutouts such as this: Maybe it refers to a modern version of something like that that you see in the NBA a lot when people break noses or otherwise want to protect their face:
Maybe its something like this? I can't see why these would be illegal. I see players with them occasionally (usually younger kids) but couldn't understand how they would be dangerous...
Since I used to work construction, I imagine it to be something like this. http://www.abcsafetyglasses.com/b26uneyesh.html HTML: <img src="http://www.abcsafetyglasses.com/b26uneyesh.html" alt=""/>
Definitely outdated terminology. Yes, what Dayton Ref shows would be 'spectacle guards,' as would any big goggles, like you would see in chemistry class, worn with or without regular glasses under them. Basically, what's prohibited is anything that projects away from the face. However, a custom molded face mask, like what RichM shows is worn in the NBA, is legal IF the referee sees a medical release signed by an 'appropriate healthcare professional.' See rule 4.2.8.
When I played racquetball in the 80's, it was common for people with glasses to wear a plastic cage that fit over the spectacles. This would protect the glassess from the ball--and not much else. I tried to find this item online just now, but apparently they are obsolete. (I would not have worn them within a mile of a soccer field.) To replace this plastic cage style of eyeglass protectors, manufacturers have modified the high school chemistry style of over the glass protectors--as shown above. This style is suitable for handball, racquetball, and squash, but pretty obviously not suitable for soccer.