Lois Lane: Jimmy, give me back my dress.
Clark Kent: Now there's something you don't hear around the newsroom everyday.
Lois Lane: You still think I'm crazy?
Clark Kent: I think you're brilliant. But there is a fine line between brilliance and lunacy.
Lois Lane: So you're saying you would never lie to your wife, that's assuming someone would actually be crazy enough to say "I do' to you?
Lois Lane: I win, you lose, we're both happy.
Jimmy: How could you see that from all the way over there?
Clark: I have a... really strong prescription.
Perry: Jimmy, I did not become editor of a major newspaper because I can yodel.
Lois Lane: So, how did I rate as a date?
Clark Kent: Oh, A-plus.
Lois Lane: I hung on your arm decoratively.
Clark Kent: You did.
Lois Lane: Fawned appropriately.
Clark Kent: Absolutely.
Lois Lane: And just faded into the background during your big moment.
Clark Kent: You were beautiful, but invisible.
Lois Lane: Mmm, make me go through another night like that, and I'll rip out your spleen.
Clark Kent: The point is you are the same reporter you have always been. Hard-working. Dedicated. Maybe a little over the top sometimes. You could use some more vacations. Maybe a semblance of a life.
Lois Lane: Is this leading anywhere?
Clark Kent: Lois, you are the best reporter in the city. You always have been and you always will be.
Lois Lane: Well, you two are invited to my house for Christmas dinner tonight.
Perry White: Well that sure beats the soup kitchen.
Lois Lane: Don't get your hopes too high.
Lois Lane: You took advantage of our privileged interview session to steal highly incriminating evidence from an unsuspecting subject... Oh! I love that! Mmmm.
Tempus: Oh please, I'll go to jail, I'll strap myself into the electric chair, just don't make me listen to this.
Answer: I don't recall if it was ever mentioned in an episode, but it's possible that the frames and/or lenses of his glasses are lined with lead, the one compound his X-ray vision can't penetrate. Speculative, of course, but it likely would have been done at a point in his youth when he wasn't in complete control of his powers.
Cubs Fan ★
I think the other answer has good speculation. I would add it could also just be an "acting gesture" that Dean Cain utilizes as part of his Superman character and not because there's any practical reason. That way, the audience immediately recognizes what he is doing.
raywest ★