This picture shows (once again) a eye. Drawn with pencil on paper. While the eyelids and eyelashes are drawn normally, this time I put special emphasis on the iris. This ring of muscle works like the iris of a camera: the more light there is (i.e., the brighter it is), the more the iris spreads out - with the result that the pupil becomes smaller. This makes the visual image on the inside of the eye (on the retina) sharper. The darker it is, the more the ring of the iris contracts - as a result, the pupil becomes larger and more light enters the inside of the eye. However, this makes the image on the retina blurrier.
A person's iris is always individual and unique. An iris scanner is just as reliable as a human fingerprint. Therefore, what is special about a drawing of a human eye is ultimately the pattern that you draw in the iris.