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.