Two difficulties with antireflective coatings are worth mentioning. One, the coatings are relatively soft and scratch easily. The lenses should be treated like CR-39 plastic; patients should always wet the lenses before cleaning and dry the lenses with a soft cloth or facial tissue. The lenses may be abraded easily if kept in a pocket or purse without the protection of a case. Second, the lenses get dirty easily. Because the lenses reflect so little light, water spots, oil smudges, or fingerprints, which increase reflection, are more visible than for uncoated lenses.