Eye corrector is the modifier, that helps to fix various issues with eyes.

Fix 1: Prevents eyelids from falling (intersecting) with eyes 

Fix 2: Adds bump over eye cornea:

Fix 3: EXPERIMENTAL prevents eyelids from overlapping

On a technical level, this is a Geometry Nodes modifier. It retrieves the vertices that you add to a vertex group, measures the initial distance from the center of the eyeball to each vertex, and maintains that distance to ensure that the vertices do not move inside the eyeball or drift too far away. Self-intersection is more complex, but it is also managed through Geometry Nodes.