Are you still on the Isle of Despair? If so, you need to travel back to the mainland; the Wheel Clan is on the main map, at the foot of the Grey mountains to the north and west.
More to the point, you don't need to kill Thorvald to get the glasses; all you need is two (possibly three) ranks in Persuasion. Or you can make your own pair by... (highlight for spoilers)
[SPOILER]...bringing 1,000 gold and a Kathorn crystal to the spectacle maker, in the shop behind the Elven trader on the Ashbury docks.[/SPOILER] (End spoiler.)
Speak softly, and carry a big stick. Or better yet: a big, sharp blade