Evaluation of a new direct-comparison aniseikonia test

Aniseikonia is a condition in which the two eyes perceive images of different size or shape, causing a variety of visual symptoms including asthenopia. Besides anisometropes (with a prevalence of 5-10% in the population above age 20 years), also pseudophakes and refractive surgery patients are at risk. For example, 40% of the pseudophakes seem to suffer from aniseikonia. Reliable measurement and management of aniseikonia is therefore important. The "Aniseikonia Inspector" is a new, commercially available, software product to measure and manage aniseikonia. The purpose of this study is to evaluate this aniseikonia test of the Aniseikonia Inspector.

Aniseikonia was induced in four subjects, with normal vision, by means of afocal size lenses. Using the Aniseikonia Inspector, the resulting aniseikonia was measured in vertical, horizontal and diagonal directions.

The average ratio between the measured aniseikonia and the induced aniseikonia was 0.98, 0.89 and 0.93 respectively for the vertical, horizontal and diagonal directions. For two consecutive measurements of the same aniseikonic state, the difference in measurement value was 97%, 75% and 94% of the time within one resolution step size (0.5% horizontally and vertically, and 0.7% diagonally).

Aniseikonia was measured accurately. Measurements in the vertical direction were more accurate than in the diagonal or horizontal directions, which is probably due to fixation disparities. The Aniseikonia Inspector is a very useful new tool in treating the growing number of aniseikonia patients.