[Management of unilateral refractive errors with contact lenses]

The degree of aniseikonia with the correction of unilateral aphakia is mathematically and clinically much greater with glasses than with contact lenses. It is not possible to estimate the resulting aniseikonia on an individual basis from calculating the right-to-left difference between the retinal image sizes. However, both calculation of the differences between the retinal image sizes and the aniseikonia point out the advantage of contact lenses. Unilateral axial myopia (more than 90% of anisomyopias are axial) shows the smallest differences between retinal image sizes for glasses; however, measuring the aniseikonia with the phase difference haploscope shows the smallest amount of aniseikonia for contact lenses. This apparent contradiction can be explained by the "expansion" of the "granularity of perception" of the more myopic eye. Because the amount of "expansion" varies widely between individuals and is not known in particular cases, aniseikonia cannot be calculated but must be measured. Aniseikonia proved to be one of the most important factors in the development of amblyopia of the more myopic eye. Contact lenses are the best means of reducing the amount of aniseikonia in patients suffering from axial anisomyopia. In cases with minor anisomyopia it may be also possible to obtain a minor degree of aniseikonia with glasses. Exceptions such as "useful" and "malignant" anisomyopia must be taken into consideration.