According to @Oh_benibeni, the image on the left resembles characters from the anime franchise Slayers, which started as a light novel series in 1989.
The transition from past to present in the world of Japanese animation is certainly an eye-opening experience.
According to the illustrator, the image on the left shows how eyes were drawn long ago, with a vertically long oval shape and lots of white space around the pupils.
One Twitter user even gives several concrete examples that correlate with Saito’s illustration.