and Hofmann in 1935. However, Nagel described it 30 years prior to Bielschowsky when he noted that the combined action of the superior rectus muscle and the superior oblique muscle of one eye and of the inferior rectus and inferior oblique muscles in the fellow eye causes incycloduction and excycloduction. The procedure that we now follow was given by Marshall M. Parks. References Further reading External links Park's three-step test Diagnostic ophthalmology Human eye anatomy Medical signs Neurology procedures