I clean eyepieces every day in a shop. I use that which does no harm to the eyepieces at all:
Q-Tips and isopropyl alcohol, or ROR (
www.ror.net).
No residue is left by the Q-tip if you mop up the dampness from the first one with the dry end. If you have to use a second Q-tip, you used too much fluid. Some eyepieces get so dirty you may have to clean twice (or more!) to get them clean. I've cleaned off mascara from my Naglers, which is why I use ROR (it's a better cleaner).
Blue Windex with ammonia D will also work fine.
Never spray or drop on the eyepiece--always dampen the Q-Tip first.