The TUSA Bifocal Lens is a single tempered glass lens with a corrective section in the lower portion of the lens only. If you struggle to read things close up like your dive computer or gauges but don’t need any help with distances then these are perfect. The main portion of the lens has no prescription but you can choose the power of the lower portion of the lens. Bifocal lens to fit TUSA Ceos, Geminus, Splendive IV or Splendive II masks and the Scubapro Zoom Evo Mask. PLEASE NOTE: These lenses are sold singularly, please order one for each eye required. The left and right lenses are not interchangeable so the left will only fit over your left eye and likewise for the right. The measurement you need from your prescription is the Add or Near reading and you need to combine this with your spherical reading. Please consult your optician if you are unsure of which strength to choose, they are the best qualified to advise. Specifications Optical lenses will replace the original lenses fitted to your mask. If you want to fit prescription lenses to one of TUSA’s Pro Masks you willl loose the AntiReflective and UltraViolet benefits of their lenses.