Aniseikonia

Translated from Greek, aniseikonia means “unequal images”. Aniseikonia is an eye condition that causes each eye to perceive the size of objects differently.

What is aniseikonia?

Aniseikonia occurs when the perceived image of each eye is different in sizes. Often, this is because each eye has a different prescription. For example, one eye might be significantly more short-sighted (myopia) or long-sighted (hyperopia) than the other, so one eye is essentially ‘seeing’ differently to the other.

The brain needs a similar image from each eye to be able to merge the two together and form a single, complex 3D image. If the image from each eye is too different, the brain won’t be able to merge the two together to form single vision; hence double vision occurs. The brain can’t process double vision, so it will ‘turn off’ or suppress the image from one eye (usually the image that’s the most abnormal); resultings in amblyopia or ‘lazy eye’.

Types

There are two types of aniseikonia: static and dynamic.

- Static aniseikonia: where the size of an image is different in each eye.

- Dynamic aniseikonia: is similar but with movement and occurs when the eyes are forced to track vertically and laterally, at different speeds.

Both cause a visual displacement between the left and right eye, so that images appear to be overlapped (or double vision) - this is because of the differences in the perceived size between the eyes.

Causes

Aniseikonia can happen naturally, or as a side effect/ unintended consequence of eye surgery (like cataracts) or wearing non-prescription or traditional glasses. 

Corrective lenses - prescription glasses and contacts, are an incredible invention that have given us improved vision for literally hundreds of years. Though, traditional glasses aren’t without their flaws, especially in the case of aniseikonia.

Traditionally, the thinking was that each lens of your glasses should provide clear vision, on its own. If an image was clear in both eyes (independently) then our brains presumably could figure out the rest. This is a monocular approach (where you’re focused on only one eye, like half a pair of binoculars), but our brains are in fact wired for binocular vision (both eyes working together, like in a set of binoculars). We see with both eyes working together, in tandem, not as two separate feeds.

With traditional glasses, the brain has to constantly adjust and find work arounds for these different images. Which results in the brain working overtime and constantly struggling to force the focus in our eyes, otherwise stopping one of the eyes entirely.

Other causes can be:

- Retinal aniseikonia: can occur if you have retinal damage, which causes a distortion in size perception (i.e. macular degeneration)

- Neurological issues such as damage to the occipital lobe in the brain, which are located at the back of the head and are responsible for visual perception; can also cause aniseikonia.

- Age: an adult can acquire aniseikonia with age, for example if each eye was to age differently - with one becoming more myopic (short-sightedness) and the other more hyperopic (long-sighted).

Symptoms of aniseikonia

Symptoms can include:

  • Double vision
  • Headaches
  • Dizziness
  • Being disorientated
  • Watery eyes
  • Sore or tired eyes
  • Being sensitive to light
  • Having trouble reading
  • Nausea

 

Binoculars med

Our brains are wired for binocular vision, both eyes working together. Not two separate feeds.

Treatment 

The most common treatments for aniseikonia are specific aniseikonic prescription glasses. Sometimes vision correction surgery could be recommended or switching from traditional glasses to contact lenses, as your symptoms can decrease with the lens sitting much closer to your eyes. 

Shaw Lenses are a highly recommended option and often used as they are specifically designed to correct aniseikonia (these are called aniseikonic lenses).

Shaw Lenses (aka Glasses 2.0)

Shaw lenses are a huge leap forward for our eyes and vision. Using advanced algorithms (a process or set of rules to be followed in calculations or other problem-solving operations, like how Netflix knows which shows to recommend to you, based on your preferences and what you’ve watched before and did or didn’t like); and analysing each eye, the Shaw lenses model the eye rotation so they can predict and prevent the distortions created by traditional lenses. 

In a nutshell, these lenses take into account how your eyes work together (not separately like we mentioned earlier), to truly deliver binocular vision.

Wearing Shaw lenses will give you a much greater field of binocular vision (both eyes working together), that is much clearer and literally easier on your eyes, and your brain. Your brain won’t need to work in overdrive (as mentioned earlier) to interpret what you’re seeing; meaning you can enjoy clearer vision with less distortions.

Book an appointment

If you think you might have aniseikonia, book an appointment. Your optometrist will work with you and create a tailor made solution, based on what’s right for you and your eyes.

BOOK AN APPOINTMENT

FAQs

Who’s at risk of developing aniseikonia?

Although approximately 20-30% of people who wear glasses may have a small amount of aniseikonia, only 5-6% are clinically significant. It’s considered clinically significant when the difference is greater than 0.75%.

With aniseikonia, there are no common or related factors, such as gender, age or ethnicity.

 

How is aniseikonia diagnosed? 

Your optometrist will conduct different visual tests, as part of an eye examination. To diagnose aniseikonia, there are specific tests that focus on the perception of binocular space, and directly compare image size as perceived by each of your eyes. 

If you think you have aniseikonia or are concerned about your eyes, please book an appointment to see one of our optometrists.