Is there any way to mirror only selected parts of a shape key? I'm modifying a model and trying to add simple expressions like blinking and etc.

I'm trying to mirror a closed eye to the other side, but it causes the whole model to become symmetrical, I can't figure out how I can only mirror selected parts :|

Here's an example:
https://www.youtube.com/watch?v=Qd4rqPp6hW0&amp;feature=youtu.be

You can see his head shape and and parts of his cheeks are getting symmetrical

edit:
another example, the difference between the basis shape-key and the mirrored one:
https://gfycat.com/ThirdHealthyGalapagosdove

Thanks in advance!
Other answers so far are good, but it's worth pointing out another technique.
There's an easy way to restore part of a shapekey to the basis shape, using &quot;blend from shape&quot; operation.  You can use this on parts of the mesh to &quot;unshape&quot; bits of the mesh.
Select the shapekey, then enter edit on the mesh.  Select all vertices of the shapekey you don't want (or select the bits you do want, then select inverse.)  Use a &quot;blend from shape&quot; operation, which I always call from the searchbar.  On the operator panel, specify Basis as the shapekey, set the blend to 1.0, and disable Add.  This restores the selected vertices to the Basis shape, making it so that some of your shapekey will be &quot;unmirrored&quot;.
You can of course use this operator for a lot of other things as well.