Op (short for “Optical”) Art was an international movement which came to prominence in the 1960s. Op artists, such as Josef Albers, Victor Vasarely, Bridget Riley, Julian Stanczak and Richard Anuszkiewicz, explored the ways pattern and color can stimulate and confuse the eye.  Web resource here.

Richard Anuszkiewicz. The Burning Glass. Oil on canvas. 1961. Private Collection.