Too often the subject turns their head in such a way they have to strain to look at the camera. This causes the pupils to be off center showing too much white. When viewing an image, the viewers eye is drawn to the brightest area of the photograph,in this case, the white of an eye. Other than looking uncomfortable, it just looks creepy seeing too much white.
A Simple Fix
A simple tip to ensure a better portrait is to center the subject’s pupil with the whites of their eyes. Have the subject turn their head and shoulders to balance their eyes.
If you have a subject that continues to show too much white, don’t delete the image. Show them during the shoot and have them correct it. When they compare the two images they should notice their image looks much better when the whites of their eyes are balanced.