Trident Stick-on Optical Lenses provide snorkelers and divers a simple and affordable way to increase the magnification in diving masks. No longer is a complete prescription mask necessary to read your fish ID card, watch, or camera settings. These glass stick-on lenses with optical quality are replaceable and reusable if you switch masks, but they won't unintentionally wash off if your mask gets wet. There are two semi-circular lenses in each package, and any snorkeling or diving mask with flat lenses can be equipped with these lenses.