It's not just a pair of glasses that helps keep Superman's secret identity a secret. An ally of the Man of Steel let it slip how Clark Kent used his powers to keep his double life hidden for so long.
The idea of a secret identity is almost as old as superheroes themselves. In order to keep their work separated from their private lives, as well as protect their loved ones, heroes use their costumed alter egos to hide their good deeds and live normal lives. No one has a more well-known secret identity that mild-mannered reporter Clark Kent aka Superman. For years, the Kansas farm boy fooled the world at large with his thick glasses, terrible posture, and fuddy-duddy nature. Anyone who looked twice at Kent never would have suspected someone so plain could ever be the protector of Metropolis.
And yet, the mousy image of Clark protected his secret for years. But, it seems that Superman's disguise has an extra layer of protection. In Superman #687 by James Robinson and Renato Guedes, Superman has departed Earth for New Krypton and left Mon-El to defend Metropolis in his stead. While the hero part comes naturally to Superman’s protégé, Mon-El seems to struggle balancing his own secret identity. The Guardian, a hero Clark entrusted to guide Mon-El, informs Mon-El that he needs to do better at slipping away from his other job as a Science Police officer. It's revealed that Superman implanted a device in Mon-El's neck that would help him hide his private life as 'Jonathan Kent.' The device allows Mon-El to replicate an ability Jay Garrick, the Golden Age Flash, pioneered. By vibrating his head just enough, Mon-El can keep his facial features as nondescript as possible.
While Mon-El gives credit to the Flash for this secret identity trick, it's a method that Superman has no doubt relied on himself. If Clark didn't see the validity in the method, he never would have given Mon-El an implant to replicate Garrick's ability. And while Superman may not have thought of the technique first, it goes a long way in explaining how he'd be able to keep his private life as a Daily Planet reporter a secret for so long.
Clark Kent's disguise has often been met with ridicule over how transparent it seems, but the truth is he puts in a lot of work. Superman’s secret identity is more than just glasses. It’s his mannerisms, posture, speaking voice, a million tiny little details that add up to an image that doesn’t exactly scream ‘Man of Steel.’ But it doesn't hurt to have a fail-safe and constant slight vibrations to give Clark a more 'everyman' appearance is just as good a method as anything else. While the idea of a constantly shifting face might seem exhausting, it's the sort of thing that's kept Superman's biggest secret safe for years.