Entoptic phenomena are visual effects whose source is within the human eye itself.

Jan Evangelista Purkyně was a Czech anatomist and physiologist. In 1839, he coined the term "protoplasma" for the fluid substance of a cell. He was one of the best known scientists of his time. Such was his fame that when people from outside Europe wrote letters to him, all that they needed to put as the address was "Purkyně, Europe".