Schneider's inexpensive, classic Xenar asymmetrical, anastigmatic, 4-element, 3-group lens design was introduced in 1919, and is largely unchanged from the original ZeissTessar formula.
From the en.wikipedia.org
In the nineteenth century, opticians dug to the level of the Seidel aberrations, called mathematically the third order aberrations, to reach basic anastigmatic correction.