I’ve made this joke many times, but nobody laughed.
It made sense to me. Glasses are lenses. Lenses need to be clean in order to perform their function. If you a photographer has dirty eyeglasses, how could you possibly trust them?
But I missed something important.
For one, glasses that are dirty are still better than no glasses at all. I should know. I am practically blind without optical correction. My glasses are filthy on occasion, but when they are, they are still better than uncorrected vision.