(Posted January 2005)

The typical goal of laser eye surgery is to produce what's called an emmetropic cornea, where the correct amount of tissue is removed from the treated area of the cornea (called the programmed optical zone) and the eye is left with no refractive error, and no need for eyeglasses. If both eyes are emmetropic, as planned, the images in each eye will be the same size.

However, if too much or too little tissue is removed, the eye ends up far(long)sighted. If this happens only to one eye, the image in that eye may be smaller than the image in the other. There are various other scenarios of under or over correction and this is just one practical example.

Similarly, regression can cause aniseikonia, particularly if the patient was far(long)sighted to begin with, achieved the appropriate correction in one eye (or became myopic in that eye) but regressed back to hyperopia in the other.

Finally, i rregular removal of tissue is another possible cause of aniseikonia. There have been reports of cases where all but the very most central part of the cornea appeared to be underablated and where the patient complained of a very small image in the affected eye(s).