Agree with Henry completely. I always keep a 'micro fiber' cleaning cloth handy for such an emergency. These days even shops selling spectacles give free swatch of micro fiber.Two caveats: 1. do not use force while wiping.Gentle is the word.as gentle as wiping the face of a baby or babe! 2.Keep the soft cloth in a small zip bag to prevent dust getting stuck on them. Otherwise it will do more harm! .