Aniseikonia generally starts to become problematic when it becomes larger than __________%.

• A. 1%
• B. 2%
• C. 3%
• D. 4%

Answer: (C)

Aniseikonia is a difference in the perceived size of images between the two eyes. The binocular system relies on matching image size and alignment to fuse the two images into one. When the magnification difference gets large enough, the images no longer line up well for fusion, so eye strain, headaches, diplopia, and a loss of comfortable depth perception can occur.

In practice, the visual system can tolerate small size differences, but once the anisokinetics cross about 3%, many people begin to notice symptoms and fusion becomes harder. Some individuals may adapt a bit more or less, but around this 3% threshold is where problems commonly start. So, 3% is the typical tipping point for when aniseikonia becomes problematic.