Compression is not a defect in the lens or mirror itself but is a warping of the lens or mirror producing warped images. It is caused by applying too much pressure around the lens or mirror's outer circumference when mounting the lens or mirror in its tube.  The remedy is obvious, don't force the lens or mirror into a tube of insufficient diameter to hold it.
Cheap eyepieces are plagued by all the above aberrations and a couple of new ones, like problems with Curvature of field and Distortion. Curvature of field brings the images of stars that are in the central regions of the field of view to a different focus than the stars in the outer regions of the field of view.
There are two types of distortion: Pincushion, and Barrel.  The latter is the one most likely encountered in a telescope. It produces a field of view that looks like everything is being viewed through a photographer's fish eye lens and would make the Lunar Eclipse look like the inset.
The best remedy for these problems is to buy better eyepieces.