Aniseikonia is a condition characterized by differences in the size of images seen by the right and left eye. The condition is often linked to visual complaints such as headaches and double vision. Various factors can cause aniseikonia, including a difference in the refractive error of each eye, a difference in the axial length of each eye, a difference in the astigmatism of each eye, or a low density of photoreceptors in one eye.
Refractive Error as a Cause of Aniseikonia
Aniseikonia is commonly caused by a difference in refractive error between the eyes. Refractive error refers to how near or far-sighted an eye is when compared to a standard eye. Nearsighted eyes can result from the eye being too powerful or the eye being too long. Farsighted eyes, on the other hand, can result from the optics being too weak or the eye being too short.
When using glasses or contact lenses to correct for refractive error, aniseikonia may occur. Nearsighted eyes with glasses may form smaller images than standard or farsighted eyes. A difference of 3% in size or about three diopters of power can usually produce a noticeable size difference. However, most people do not experience aniseikonia issues even with differing prescriptions since both eyes are similar even if not identical.
Refractive differences after having surgery – usually to remove the crystalline lens – are much greater and tend to lead to aniseikonia more often. This is why lens extraction is often done bilaterally or a contact lens is worn in the eye that has had the lens removed.
Astigmatism as a Cause of Aniseikonia
Aniseikonia can also be caused by astigmatism, an eye condition that causes the eye to focus on two points rather than one. If one eye has significant astigmatism and the other does not, meridional aniseikonia may occur. The difference between the astigmatism needs to be greater than about three diopters, which is similar to the refractive error differences.
Aniseikonia due to Photoreceptor Density
Aniseikonia can also result from the density of photoreceptors or retina vision cells. If one eye has a higher or lower density of photoreceptors than the other, it can cause differences in size. This type of aniseikonia may be present at birth and is often associated with specific genetic disorders.
To correct aniseikonia, eye doctors can prescribe special glasses with characteristics to reduce the size difference between the eyes. The eye doctor may recommend contact lenses or glasses if the size difference associated with glasses is the cause of the issue.
While various factors can cause aniseikonia, such as a difference in refractive error, astigmatism, or photoreceptor density, the use of contact lenses or glasses to correct these differences can reduce aniseikonia symptoms. The symptoms of aniseikonia may seem to be subtle, common, or even unrelated to the eyes, but discussing any potential symptoms with your eye doctor will allow them to better help you. If you experience any visual complications, it is recommended to consult with an eye doctor to identify and manage potential conditions.