Parks–Bielschowsky three-step test

The Parks–Bielschowsky three-step test, also known as Park's three-step test or Bielschowsky head tilt test, is a method used to isolate the paretic extraocular muscle, particularly superior oblique muscle and trochlear nerve (fourth cranial nerve), in acquired vertical double vision. It was originally described by Marshall M. Parks.

Source: Wikipedia — Parks–Bielschowsky three-step test (CC BY-SA 4.0)