Hydrotac® Stick-on Bifocal Reading Lenses Hydrotac™ lenses turn any glasses into magnifying glasses with superior clarity. Just add water and adhere. Lenses are 3cm in diameter and are removable, reusable. Great for those who require magnification for eyewear that is not prescription, like sunglasses. Hydrotac™ lenses can be trimmed to size with a sharp scissors and positioned anywhere on the lens. Use the included protective case to keep them safe when not in use. A larger size is available for diving masks.