IST Prescription Mask- Optical Corrective Scuba Diving Snorkeling Mask - Rx Prescription- Bk, Yellow, Blue, Bk Silicon Low in profile and internal volume with Great IST Quality! Ideal for medium faces (fits almost everyone) Crystal, liquid silicone injected skirt and strap, Double edge comfort seal, Ultra low volume. Broad peripheral view. Tempered glasses. Prescription optical lens available