Aniseikonia
What Aniseikonia Is
Aniseikonia is a binocular vision disorder that causes a difference in perceived image size between the two eyes. Basically, everything in one eye is perceived as larger or smaller than the other eye.
Patients will often describe their symptoms as double vision or say that their one eye is “pulling.” This description usually leads a practitioner to turn to prisms as the solution. Where prisms are a fantastic way to solve for double vision, they don’t help when there’s a size discrepancy.
As you can see in the image, double vision is the inability to unify images perceived in both eyes. Aniseikonia is two different sized images laying on top of one another. You have to correct for the size difference, not the image location.
Two Types of Aniseikonia
There are two main types of aniseikonia: Optical and Retinal.
Optical aniseikonia is, generally, easier to diagnose as it will likely show up in the refraction. If the prescriptions for each eye are vastly different and they’re complaining about double vision or “pulling,” it’s likely aniseikonia.
Retinal aniseikonia can be more difficult to diagnose as it’s likely the result of a past eye surgery or retinal disease. For this, you’ll have to investigate the patient’s medical history.
The point is: if it’s not obvious from the refraction, it’s still possible that it’s aniseikonia.
What it Feels like - Symptoms of Aniseikonia
As stated above, patients will often describe their symptoms as double vision, one eye “pulling” or just simply “bizarre.”
Other symptoms of aniseikonia can include:
- Headaches
- Eye strain
- Difficulty with depth perception
- Disorientation or dizziness
- Reading difficulties
- Suppression of vision in one eye
The severity of symptoms often depends on the degree of size discrepancy. Even a 1-2% difference can cause discomfort, while differences over 5% can be highly problematic.
Options to Consider When Treating Patients with Aniseikonia
The primary and most effective solution for people with aniseikonia are glasses that equalize the image sizes between the two eyes. Here are some options to consider:
- Magnifying or minifying lenses: These magnify or minify the size of the image and are adjusted via the base curve of the lens, its thickness or the distance from the eye.
- Spectacle magnification: These take the naturally occurring magnifying or minifying effect of a lens and are then carefully adjusted to spectacle magnification per lens to match image size.
- Choice of lens material: Different materials have different refractive indices, affecting magnification.
- Lens position: Where the lens is placed in terms of the lens-eye distance can affect and correct for magnification discrepancies.
- Iseikonic lens: These are specially designed for aniseikonia and can have different front and back curves to achieve the right magnification without changing the prescription power.
- Size lenses: These have no refractive power but are shaped to magnify or minify and are combined with regular prescription lenses.
- Contact lenses: These would be used in conjunction with glasses to correct the refractive error while the glasses handle the size difference.
- Addressing shape distortion: These can be designed to correct for size AND shape distortion.
As you can probably imagine, given the above information, the process of fitting glasses for aniseikonia is quite complex and requires taking the following steps:
- Measure the degree of aniseikonia
- Calculate the needed size adjustment (link to aniseikonia calculator)
- Design lenses to achieve this adjustment
- Fine-tune based on patient feedback
How We Help: Aniseikonia Size Lens Kit
Aniseikonia can be tough to work with. It often feels like a moving target. Sometimes, no amount of testing can beat a patient’s subjective feedback. Chadwick’s Aniseikonia Size Lens Kit contains a series of afocal (plano) lenses that contain only magnification. Our standard kit contains 5 different magnification lenses, 1%, 2%, 4%, 5%, and 7%, but can be customized upon request. You and the patient can experiment to find the best combination of lenses to help relieve their symptoms.
How to Use Size Lens Kit
Size lenses are miniature afocal telescopes. By looking through the lens with a convex side, away from the eye, the user will view the image as slightly larger. By flipping the lens, it will make the image slightly smaller.
Stacking Size Lenses
Because the scopes are afocal, they can be stacked to measure different amounts. By holding the 1% and 2% scopes together, it makes the magnification 3%.
Ordering Rx’s with Size Component
Size lenses should be used over the patient’s refraction. When manufactured, we typically want to add the magnification to the smaller eye. There may be exceptions on the higher Rx’s.
You would order magnification in addition to refractor, i.e.:
OD +100 +5% magnification
OS +100
Need to do some calculations? Save yourself some work and use our Aniseikonia Calculator! Need some help or want to chat about your case, give us a shout.
Ready to order the Size Lens Kit? Click to visit our Size Lens Kit product page or give us a call.
