Localized defects in ophthalmic lenses

Ophthalmic lenses made from glass, hard resin, and polycarbonate are inspected with a shadowgraph to determine the nature, frequency, and severity of localized defects, including power aberrations. The most common localized defects are scratches and pits left by incomplete polishing and localized power aberrations caused by variations in the thickness of scratch-resistant coatings. Localized defects are more likely in polycarbonate lenses than in glass or hard resin lenses. The compliance of lenses with standards that limit localized defects is discussed.