Entoptic phenomena are visual effects whose source is within the human eye itself.
Purkinje tree depiction
Hermann Ludwig Ferdinand von Helmholtz was a German physicist and physician who made significant contributions in several scientific fields, particularly hydrodynamic stability. The Helmholtz Association, the largest German association of research institutions, is named in his honour.
Hermann von Helmholtz
Helmholtz's polyphonic siren, Hunterian Museum, Glasgow
Helmholtz in 1848
1889 copy of Helmholtz's "Uber die Erhaltung der Kraft", no. 1