[Principles in correcting unilateral aphakia to preserve binocular functions].

A new concept for correcting unilateral aphakia has been developed for patients able to accommodate. This concept is based on the investigations of binocular tolerance observed in aniseikonia. The test method for binocularity should have a retinal image of adequate size and should respond sensitively to limitation of vertical disparity. These criteria are satisfied by the TNO test for stereopsis. The retinal image size can be assessed using a spectacle-contact lens combination similar to an inverted Galilean telescope system. The image size can be reduced as long as the patient perceives positive stereopsis by the TNO test. Some typical cases are discussed. In patients who had had conventional contact lenses fitted more than 2 years previously it was no longer possible to obtain positive TNO values.