You already know my friend Gary Tu, a fashion illustrator from Taiwan. These days I will write some posts inspired by his drawings and fashion illustrations. First of all, here are some stages that you must follow in order to paint the eyes.
It is important to guide your hand in these 3 directions suggested in the image below. Go up, then oblique and then go down, like the arrows are pointing.
Then use the brush with a lot of water, just to make sure you will create the shadow effect of the bottom par of the eye. There is no need to add color or extra-black ink. All you have to do is to dilute the brush and simply leave marks with the brush filled with water.
Then paint an almost dot/circle and make sure to leave an area where you will add the black dot for the pupil. Do not fill the entire space of the diluted dot. You will need that space in order to create the white, trans-lucid part of the eye, the glitter of the eye.
And once again, at the end, after you will be used to paint the eye on these stages you will be able to paint the eye using only 4 strokes: a rounded, upper one, a rounded shape down, the almost dot and the black point that will create the pupil of the painted eye.
Hope this will help you paint the eye and it will reply to your questions regarding: how to paint an eye in watercolors?
Once again, many thanks to Gary Tu who provided his painting for this tutorial.