TRSE: How To Draw Tutorials:
All about the Eyes in Animanga

    In most cases, the shape and sizes of the eyes are determined by gendar and age. For example, female characters tend to have larger eyes ("cute look") while male characters tending to have narrower eyes. Younger people especially children tend to have large eyes that shrink as they grow up (or mature).

a male character of 
FullMoon O Sagashite
female character of 
FullMoon O Sagashite
Tsume, an adult of 
Wolf's Rain
Yuki, a child
of Bleach
    It is very common for the female characters to have big eyes, but some boys can have large eyes especially when those eyes are to make them look young or give them the "girlish look". It can be said the same for some female characters where the narrow eyes can make them seem mature, older or more serious. The size of the eyes also can hint at the age of the characters as shown by the picture below:
Kiba and Hige of Wolf's Rain
    Both Hige and Kiba are male characters but Hige looks younger because of his larger eyes while Kiba looks older and more serious.
    The artists' preferences can shape the way they draw the eyes. If an artist likes to draw large eyes, then the male characters would have large eyes while the female characters having huge eyes! It's up to you to decide on how you draw the eyes the way you like. If you want, you can actually give a try at modifying the shape of the eyes to reflect each character's different personality. Let' move on to learn some examples of how the shape of the eyes can be determined by the characters' personalities.