Refractive surgery – a range of procedures, usually involving specialist lasers, where the shape of the cornea is changed in order to correct myopia, hypermetropia and astigmatism. Additionally it is possible to insert an intraocular lens behind the cornea which can also correct presbyopia in addition to the other common visual problems. There is no doubt that the majority of patients have been very happy with the results so far, however a minority have suffered problems and the long term prognosis for such surgery is uncertain. The main refractive surgery companies in the UK are Ultralase, Optimax, and Optical Express. See also RK, PRK, Lasik, Lasek, Clear lens extraction.