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: I know you may not believe this, but there was a time where I had to be the best at everything.
Lois Lane: What kind of person keeps a body frozen in a glass case?
Clark Kent: Somebody who's having a hard time getting a date?
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.
Superman: You know, people who love each other are supposed to be kind to each other.
Lois Lane: Even when a huge part of you didn't make any sense, there was a part deep down that did.
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.
Lois Lane: Tell me the biggest secret you have.
Clark Kent: What?
Lois Lane: Tell me the biggest secret you have. Something you'd never reveal to anyone.
Clark Kent: Why?
Lois Lane: Because I'm about to tell you mine and I need blackmail material.
Lois Lane: Clark! You came. Why aren't you in Smallville with your folks?
Clark Kent: Oh, uh... my plane got snowed in.
Lois Lane: It did? But it's not snowing... Oh! You are the best.
Perry: Jimmy, I did not become editor of a major newspaper because I can yodel.
Superman: You know what's great about you?
Lois Lane: Sure, but you could repeat it again.
Superman: Everything.
Lois Lane: I only know how to make four things, and this is the only one without chocolate.
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 ★