Per the Occupational Safety & Health Administration: The preferred viewing distance for VDTs ranges between 18 and 24 inches (45.72 and 60.96 centimeters, respectively).CARE
To avoid damage, never clean your computer glasses with paper towels or clothing or alcohol, and also avoid using household detergents or soaps. While a few mild soaps don't harm lenses, today's extra strength soaps are powerful enough to slowly disintegrate lens coatings.