Aniseikonia is the term used to describe when the images seen by each eye are different sizes and it is perceived as different. This condition can lead to other perceptual issues, headaches, and cause difficulties when wearing glasses.
How Does Aniseikonia Occur?
Aniseikonia is usually due to different refractive powers or strengths of the two eyes.
For instance, one eye may need a +1.00 lens to see clearly, and the other eye need a +10.00 lens. In this case, the eye with the +10.00 lens would have 10 times the magnification in glasses.
It is uncommon for the refractive power of the eyes to be drastically different unless there is a specific reason for the difference.
Types of Aniseikonia
There are several potential causes of a refractive power difference that leads to aniseikonia.
While rare, it is possible that the eyes are both perfectly healthy except for the difference in refractive power. This case is considered to be congenital aniseikonia or aniseikonia which you are born with.
If there is a condition or disease that leads to the aniseikonia, it is said to be secondary aniseikonia.
Causes of Secondary Aniseikonia
Secondary aniseikonia can result from any disease or condition which changes the refractive power of the eye.
The most common form of secondary aniseikonia is due to lens extraction which leaves one eye without a lens. This condition is known as aphakia and can lead to extreme cases of aniseikonia since one eye is much more powerful than the other eye.
Other causes of secondary aniseikonia include microphthalmia, tumors of the eye and brain, and corneal diseases or surgery.
Microphthalmia is a genetic condition where one eye is born much smaller than typical. This leads to a difference in the power of the eyes because one eye is shorter than normal.
Tumors of the eye or brain can cause the eye to shorten and result in a similar effect to microphthalmia by having the eye be shorter than normal.
In corneal diseases or surgery, the cornea can change powers and lead to a difference between the eyes if the changes are not symmetrical.
Symptoms of Aniseikonia
The main symptoms of aniseikonia include a perceived difference between the eyes which may induce headaches, cause confusion, or reduce the 3-D vision.
Since each eye is seeing a different sized image, the brain is forced to choose between the two and may alternate between the two images.
This causes the headaches, confusion, and can lead to the perceptual difficulties that are associated with aniseikonia.
Treating Aniseikonia
To treat aniseikonia, selecting the best glasses or contact lenses is the best option.
By trialing different types of lenses or having an eye doctor or optician evaluate the aniseikonia caused by glasses you are able to find the best combination to reduce the symptoms.
There is no cure for aniseikonia, it is a chronic condition unless the condition causing the difference in the refractive powers is treated.
If you are suffering from symptoms that are like those of aniseikonia, it is important to discuss these with your optometrist.