[Fusion amplitude and aniseikonia. Experimental studies of aniseikonia tolerance in unilateral aphakia]

The fusion amplitude of image pairs with aniseikonia was measured using the synoptophore. Aniseikonia was produced in five subjects by alteration of slide drawings. The subject's right eye was in cycloplegia after paralysis with cycloplegic eye drops. To compare these measurements with aniseikonic pictures to those using the same image pairs without aniseikonia the fusion amplitude achieved was expressed as a percentage of the aniseikonia-free fusion amplitude. The relation between aniseikonia, eccentricity of the image borders and percent fusion amplitude was described using a mathematical approach. The experimental results reveal that a minimal increase in overall aniseikonia with greater eccentricities (greater than 5 degrees) leads to a rapid decrease in the fusion amplitude and the occurrence of diplopia. The aniseikonia tolerance level of images with greater eccentricities achieved experimentally and theoretically are in good agreement with results found in unilaterally aphakic patients.