Ophthalmic lenses are subdivided into monofocal lenses (provide vision for a single distance e.g. far or near), multifocal lenses (provide vision for multiple distances e.g. far, intermediate and near), lenses (near and intermediate) provide double distance vision, useful for work-related uses (e.g. office, shops, etc.). Ophthalmic lenses correct visual deficits such as nearsightedness, astigmatism, farsightedness and presbyopia and are fitted on prescription frames. These can be clear with anti-reflection, for use indoors, or for night vision such as driving. They can also be made solar, with tint for UV protection. There is also the category of photochromic lenses, which react to ultraviolet rays and provide constant protection for the eyes, adapting to all light conditions by switching from bright to dark and vice versa. Multifocal lenses differ in terms of visual performance, from the cheapest product providing more basic vision, against the high-performance top of the range with optimised and more comfortable vision.