I remembered an interview with KK talking about this and just found it. Here it is:

Sunglasses hold a lofty perch atop the list of rock-star accessories, but for Judas Priest guitarist Kenneth “KK” Downing, they also helped hide a nasty secret. When I interviewed KK in 2005 for the San Antonio Express-News, he came clean regarding his seemingly sudden fixation on eyewear.
“Yeah, that was a bit of a horror story,” he said regarding JP’s 1986 “Turbo” tour. “I had this guitar tech who cut my guitar strings off (at the tuning pegs) and left them sticking out about a quarter-inch. (Vocalist) Rob (Halford) was onstage and he twirls around and hits my guitar neck with his arm, and two of these strings punch me in the eye. My eye turned all green and I looked like something out of a horror movie. So, I wore these sunglasses, which was even worse, because the sweat from my forehead steamed up the glasses. Instead of not being able to see out of one eye, I couldn’t see out of either!”
Damn, he still looked good, green eye and all!! 
Welcome to the Board Crista!
[Show/Hide Quoted Message] (Quoting Message by spapad from Friday, September 23, 2011 9:51:26 PM) |  | spapad wrote: | | The glasses were because he broke a string and it hit him in the face. Black eye = sunglasses. lol
|  | Crista wrote: | | I love Priest... Live! stage clothes, K.K. glasses as well ;) They were so... eighties, but with a strong personality.
Stunning video performances, both of them.
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