Years ago, eyeglasses were relatively inexpensive, they were made of tempered glass, were easy to clean, and lasted forever, or at least until you broke them. Today's more expensive eyeglasses have plastic lenses with special coatings for glare reduction, ultraviolet protection and scratch resistance. They are more difficult to keep clean, and special care must be taken to avoid abrading the surface coatings or causing scratches in the plastic lenses. Eyeglasses Technique.
To minimize abrasion and scratches, first rinse your eyeglasses under running water to wash away dust and dirt particles. This would be especially important after working outdoors in dusty conditions.
Wash your hands with soap and water. Then, using a bit of dish soap or mild hand soap on your wet fingertips, gently rub the lenses to release any oily or greasy deposits.
Thoroughly rinse off the soapy residue under very warm running water. Inspect the lenses closely, and if any smudges remain, repeat the soaping and rinsing procedures.
Do not wipe the lenses dry, but rather blow vigorously on the inside and outside surfaces of the lenses, to remove any remaining water droplets. Wipe dry only the outside edges of the rims. By always following this procedure you will continue to have sparkling clean, scratch-free eyeglasses!
You can use this procedure anywhere that you have access to a restroom or a kitchen sink.
To preserve your plastic lenses avoid harsh chemicals and extreme heat.
Source http://www.ehow.com/how_4682953_clean-eyeglasses-scratches.html