[Preoperative intraocular lens power calculations in problem eyes].

The removal of the opaque crystalline lens in cataract surgery and its replacement by an artificial lens has become the most successful surgical intervention in the history of medicine. Modern intraocular lenses, today's micro-incision approach and high-end measurement and computational techniques provide restoration of good visual acuity in the majority of cases. Patients with problem eyes not allowing standard procedures for intraocular lens power calculation require special attention. Among them are highly ametropic subjects with very short or long eyes or patients, whose corneal structures are different from normal due to preceding refractive surgery. The special problems for measurement and lens power calculations in these eyes are dealt with in detail. Based on hitherto unpublished clinical data, causes and possible solutions for the existing problems are discussed. Generally, the best available measurement techniques should be applied in these cases. With respect to the algorithms used it has to be made sure that no additional errors are introduced by the algorithms themselves. The popular SRK II formula should therefore not be used any more. If errors are minimized this way, gross postoperative refractive surprises should be avoided even in problem eyes.