Cleaning Camera Lens

My camera lens is smudged from getting Blu Tack on it. I've used alcohol wipes which has made it much better, but it still doesn't seem to be returning fully to its normal quality no matter how much I wipe it.

The lens is tricky because it's such a small area, so can anyone recommend a good method for cleaning it (without damaging the lens of course)? I've been wrapping an alcohol wipe around a cotton bud so far, but I'm not sure if something more precise could help.

Is it possible that the lens is permanently ruined?