After about a year I just had to replace my eyeglasses. I keep them in a case when I'm not wearing them, and am not hard on them when I am. But I cleaned them sometimes with a tiny bit of dish detergent and water. The minute scratches caused by the detergent looked like greasy smears, which I tried harder to remove, and with more soap.
Ukulele finishes being at least as variable as optical coatings, I'd be extremely wary of anything stronger than a damp microfiber cloth. Everything may look great the first few times, but cumulatively you could be doing damage that looks like smudges, and which you continue to try to fix with polish, continually adding to the problem.
Fretboards are a different story. They can get pretty gross, but an ounce of prevention being worth a pound of cure, washing your hands before playing and a quick rub down with the damp cloth after if you have sweaty hands, should help a lot. Intuitively, it seems most oils would be safe, but intuition led me to the kitchen sink to clean my glasses, so I don't particularly trust myself on that.
