The Tilos Universal+ is the first mask in the industry to provide tool-less installation of your prescription lens. Switching prescription lenses has never been easier! Please message us at email@example.com if you choose to purchase your mask with prescription or bifocal lens with your preferred diopter strength. Full lens prescription available in Diopters -8.0 to +3.0. Bifocal lens available in +1.75, +2.25 and +2.75.