What is Non-Refractive Aniseikonia?
Aniseikonia is a condition where the perceived size or shape of an image is different between the two eyes. While it commonly occurs due to a difference in the refractive power of the eyes (refractive aniseikonia), the situation we want to highlight is when it’s caused by retinal abnormalities.
- Retinal Issues: Conditions such as retinal detachment or an epiretinal membrane can significantly affect the visual system’s perception of magnification.
- The Problem: Most importantly, these issues do not always show up in the refraction. A patient’s refraction might appear normal or nearly normal, yet they experience significant visual discomfort and imbalance.
Why Standard Solutions Fail
When you have a patient where something is clearly amiss, but the refraction appears fine, you might find yourself troubleshooting with tiny adjustments such as quarter-diopter prism changes.
- Prism Won’t Help: Prism helps align images, but it will not change the perceived size of the image.
- Refraction Won’t Help: Fiddling with small changes in sphere or cylinder often won’t correct the fundamental size imbalance.
The Overlooked Part of the Toolkit: Magnification
Magnification is a critical, yet often overlooked, part of your available toolkit when dealing with these complex cases. When a patient has a history of retinal issues and is struggling with comfort, it is essential to remember that there may be a significant magnification imbalance between the two eyes.
- The Strategy: Consider addressing this imbalance directly by using magnification – a concept you may recall from optometry school.
- The Result: By adjusting the magnification of the lens, you can equalize the perceived image size between the eyes, which is something that prism or minor changes in refraction simply cannot achieve.
The takeaway is this: Aniseikonia is not always refractive. If prism and refraction adjustments aren’t solving the problem, remember that you have magnification available as a powerful tool to address a retinal-induced size imbalance.
