aniseikonia

Aniseikonia is a relative difference in the size or shape, or both, of the ocular images of the two eyes. A difference of 0.75% or more generally causes symptoms and counts as clinically significant, although some patients have no symptoms even with large differences.¹ Aniseikonia is likely when a patient with anisometropia wears a correct prescription, and retinal disease can also cause it.² Epiretinal membrane and its treatment can shift the photoreceptors of one eye and produce a field-dependent aniseikonia, often greater than 15%, that varies across the retina.¹

The symptoms resemble those of uncorrected ametropia and heterophoria. In a series of 500 aniseikonic patients, asthenopia and headaches were each reported by 67%, ahead of photophobia, reading difficulty, nausea, and dizziness.¹ Aniseikonia is suspected when symptoms persist despite a correct prescription or appear after other problems are corrected, especially with high anisometropia or astigmatism, pseudophakia, scleral buckling, corneal transplantation, or refractive surgery.² Contact lenses are the first consideration when anisometropia is significant, but changes to base curve, lens thickness, and vertex distance can correct the size difference in spectacles.^1,2