I have significant nearsightedness (and some astigmatism), but see just fine with eyeglasses. One phenomenon I've noticed is that when I shift my head side to side or up and down while keeping my eyes focused on the same target is that different colors of light appear to move at different rates.

While it's hard to be 100% certain due to how terrible my unaided vision is, I don't think this occurs when I look at the blurry image with my naked eye, so it seems like this must be due to the corrective lenses and not something biological.

For instance, take the following image with a red, green, and blue square against a black background:

[![equidistant vertically centered red, green, and blue square on a black background](https://i.stack.imgur.com/AjrAj.png)](https://i.stack.imgur.com/AjrAj.png)

When I shift my head up while looking at the image, the three squares move at three different rates, such that the red square is lowest, the green is higher, and the blue the highest:

[![equidistant vertically centered red, green, and blue square on a black background](https://i.stack.imgur.com/AjrAj.png)](https://i.stack.imgur.com/AjrAj.png) → [![upward stepping red, green, and blue square on a black background](https://i.stack.imgur.com/t95rZ.png)](https://i.stack.imgur.com/t95rZ.png)

The inverse happens when I look downward.

Likewise, when I tilt my head to the right, the red and blue squares seem to move away from the green square, and toward the edges of the black box:

[![equidistant vertically centered red, green, and blue square on a black background](https://i.stack.imgur.com/AjrAj.png)](https://i.stack.imgur.com/AjrAj.png) → [![equidistant vertically centered red, green, and blue square on a black background](https://i.stack.imgur.com/dz6vg.png)](https://i.stack.imgur.com/dz6vg.png)

Likewise, when I tilt my head to the left, they shift the other direction, moving closer to the green square.

This also means that composite colors such as purple have colors shift in alternate directions:

[![purple square on black background](https://i.stack.imgur.com/c7a7z.png)](https://i.stack.imgur.com/c7a7z.png) → [![red-purple-blue joined rectangles on black background](https://i.stack.imgur.com/8aQyy.png)](https://i.stack.imgur.com/8aQyy.png)

I've confirmed the same behavior in the same direction occurs with both eyes.

What is causing this phenomenon?

Note: Since this appears to be due to the corrective lenses, and therefore I'm guessing not due to the underlying biological systems, I'm putting this here in [Physics Stack Exchange](https://physics.stackexchange.com) and not in [Biology Stack Exchange](https://biology.stackexchange.com).