Hess, artist and teacher, looked at my portraits early on and told me to avoid overworking the eyes. He reminded me that, as humans are social creatures, we depend in large part on our vision and on eye contact. He pointed out that, when viewing a portrait, we tend to focus on the eyes, so I need not over emphasize them.
I've found Hess's advice to be useful. This painting pushes the limit of my under-doing and it also happens to be a painting of mine that Hess rather likes.