RX BLUE SNORKELING SCUBA MASK PRESCRIPTION LENSES RX Mask - Scuba or Snorkel Most stock prescription masks shipped within 24-48 Hrs! Prescription Step Diopter lenses are stock lenses or pre-made lenses available in .5 strength increments Negative lenses adjust for the near - sighted - Available in -1.0 to -10.0 strengths. Positive lenses adjust for the far- sighted - Available +1.0 to +4.0 strengths. These lenses are perfect for snorkeling featuring lower costs ($20 to $30) than custom ground lenses