Optical Corrective Scuba Dive Snorkeling Mask Prescription Lenses ProMate Scope Scuba Dive Mask/MK245 and Corrective lens: Optical Correction lenses available from -1.0 to -10.0 by increments of 0.5 (for near sighted)./OP250 Optical Correction lenses available from +1.0 to +4.0 by increments of 0.5 (for Far sighted)./OP250 Bifocal Optical correction lenses, also called Gauge Reader available +1.0, +1.5, +2.0, +2.5, +3.0, +3.5, +4.0./OP251