Promate ProViewer Scuba Dive Purge Mask RX Prescription Lenses available Ideal for medium faces, face seal size W4 3/4 * H3 3/8. Patented purge design. Patented channeled skirt design directs bubbles away from view & Broad peripheral view. Optical lenses available from -1.0 to -10.0 by increments of 0.5 (for near sighted). Optical lenses available from +1.0 to +4.0 by increments of 0.5 (for far sighted).