Aniseikonia is an ocular condition where there is a significant difference in the perceived size of images. It can occur as an overall difference between the two eyes, or as a difference in a particular meridian. If the ocular image size in both eyes are equal, the condition is known as iseikonia. Symptoms and signs
Up to 7% difference in image size is well tolerated. If magnification difference becomes excessive the effect can cause diplopia, suppression, disorientation, eyestrain, headache, and dizziness and balance disorders. Asthenopic symptoms alone may occur even if image size difference is less than 7%. Causes
Retinal image size is determined by many factors. The size and position of the object being viewed affects the characteristics of the light entering the system. Corrective lenses affect these characteristics and are used commonly to correct refractive error. The optics of the eye including its refractive power and axial length also play a major role in retinal image size.Aniseikonia can occur naturally or be induced by the correction of a refractive error, usually anisometropia (having significantly different refractive errors between each eye) or antimetropia (being myopic (nearsighted) in one eye and hyperopic (farsighted) in the other.) Meridional aniseikonia occurs when these refractive differences only occur in one meridian (see astigmatism). One cause of significant anisometropia and subsequent aniseikonia has been aphakia. Aphakic patients do not have a crystalline lens. The crystalline lens is often removed because of opacities called cataracts. The absence of this lens left the patient highly hyperopic (farsighted) in that eye.
See also
Adelbert Ames, Jr. (Dartmouth Eye Institute, research in the 1930s and 1940s on aniseikonia)
Anisometropia
Macropsia
Micropsia

References
Further reading
Bannon, Robert E.; Neumueller, Julius; Boeder, Paul; Burian, Hermann M. (June 1970), "Aniseikonia and space perception: After 50 years", American Journal of Optometry & Archives of American Academy of Optometry, 47 (6): 423–441, doi:10.1097/00006324-197006000-00001, PMID 4912937, S2CID 37288776
Bisno, David C. (1994), Eyes in the Storm—President Hopkins Dilemma: The Dartmouth Eye Institute, Norwich, Vermont: Norwich Book Press, p. 288

External links
Aniseikonia Calculator, Chadwick Optical (U.S.A.) — a magnification calculator for iseikonic prescriptions or aniseikonia.