The illusion (inverted T), which is called the Wundt-Fick illusion at least in Japan, originates from A. Fick only, a physiologist who described it in his doctoral thesis in 1851- this is the first geometric-optical illusion.

It was documented even before Oppel, in 1854 coined the term "geometrisch-optische Tauschung" and contributed several more patterns. Although he became a famous ophthalmologist, his son may be an even more famous ophthalmologist, as he invented the first contact lenses.