Wall-eyed divergence

How it works

Your eyes turn inward when you look at something near. They turn back out to parallel when you look at something far away¹. This outward movement is called divergence. In normal life it stops at parallel. There is nothing further away than the horizon, so the eyes never need to point outward past straight ahead.

Wall-eyed divergence means driving the eyes outward on purpose. Each eye is pulled toward the ear by a muscle on its outer side, the lateral rectus. Crossing the eyes borrows a strong reflex that already exists. Divergence has no such reflex to borrow, so it is much harder. Most people cannot do it at all. Those who can usually manage only a few degrees past parallel.

The mild version is more common. Parallel viewing means relaxing the eyes to point straight ahead while looking at something close. This is the trick behind autostereograms, the Magic Eye pictures that were popular in the 1990s². Each eye sees a different column of the pattern and the brain fuses them into a 3D image.

When an eye drifts outward without control, doctors call it exotropia³. That is a separate condition. It is not caused by practising divergence.

Try it

1. Hold a Magic Eye picture or any repeating pattern at arm’s length.
2. Look through the picture, as if at a point far behind it. Let the pattern go blurry.
3. Keep your eyes relaxed. The repeated shapes should drift and overlap.
4. Once they lock together, a 3D shape appears. Your eyes are now parallel while looking at a near object.
5. To go further, try to push the outward feeling a little more. Most people cannot. Stop if it hurts.