The scuba dive Mask is ideal for medium faces, and fits almost everyone- face seal size W4 1/2 * H3 3/8. Crystal, liquid silicone injected skirt and strap, Double edge comfort seal, low volume. Made in Thailand.<br/> <p>Prescription (RX) Lens will be installed in the brand scuba mask by certified techanician.</p> <p>All lenses are tempered glasses, also called Toughened glass is a type of safety glass processed by controlled thermal or chemical treatments to increase its strength compared with normal glass. Tempering creates balanced internal stresses which cause the glass, when broken, to crumble into small granular chunks instead of splintering into jagged shards. The granular chunks are less likely to cause injury. Comparing with polycarbonate lens, it is usually heavier than the polycarbonate, but the polycarbonate is easier scratched (Most manufactures now include a scratch-resistance coating to protect the lens.) </p> <p>IF YOU NEED DIFFERENT CORRECTIVE LENSES ON EACH SIDE, PLEASE SEND US A MESSAGE WHEN PLACING YOUR ORDER.</p> <p>With a bifocal, the upper part of the lens is generally used for distance vision (NO PRESCRIPTION,) while the lower part is used for near vision with adjustment power for close-up work. A segment line separates the two section for bifocal lens type. By contrast, both farsightedness and nearsightedness are Single vision which has the same optical focal point or correction over the entire area of the lens.</p> <p>Should you have any question, please feel free to contact us.</p>