Trepanation

Trepanation (also known as trepanning, trephination, trephining or burr hole) is a form of surgery in which a hole is drilled or scraped into the skull, thus exposing the dura mater in order to treat health problems related to intracranial diseases, though in the modern era it is used only to treat epidural and subdural hematomas, as an extreme body modification, and for surgical access for certain other neurosurgical procedures, such as intracranial pressure monitoring.
Trepanation was carried out for both medical reasons and mystical practices for a long time: evidence of trepanation has been found in prehistoric human remains from Neolithic times onwards, per cave paintings indicating that people believed the practice would cure epileptic seizures, migraines, and mental disorders..Furthermore, Hippocrates gave specific directions on the procedure from its evolution through the Greek age.
The modern medical procedure of corneal transplant surgery uses a technique known as trepanning or trephining, however the operation is conducted on the eye (not the skull), with an instrument called a trephine.