The prefix "aniso-" is derived from the Greek word, "anisos", and means "unequal or dissimilar".
Anisocoria is the medical term used to describe unequal pupil size. The most common cause of anisocoria is actually something called "physiological anisocoria" which basically means there is no serious underlying reason for the difference in pupil size. Approximately 20% of individuals have noticeable anisocoria. The classic teaching is that physiologic anisocoria virtually always entails less than 1 mm difference in pupillary diameter (although greater disparities can occur). In cases of anisocoria greater than 1 mm, alternative diagnoses should be carefully considered.
Aniseikonia is an unequal magnification of images projected on the retina. The most common cause of aniseikonia is if a patient wears a pair of glasses whose lenses differ greatly in power. Most adults can tolerate about an 8% difference in image size.
Anisometropia is defined as any difference in the spherical equivalents between the two eyes. For example, if the right eye has a refraction of -3.00 sphere and the left eye has a refraction of -5.00 sphere, then anisometropia is present.
