If you want the subject to be recognized in your photo, the eyes (minimally the front-most eye), must be in sharp focus. When shooting with depth of field this shallow, Careful attention must be paid by both the subject and the photographer - neither can move after focusing.
Using a comfortable pose helps your subject remain still - and it helps them look relaxed.
Want to emphasize the subject's eye color? Shoot them in a bright environment. Ambient window light was used for this senior portrait.