This is just a quick tutorial on a simple way i like to draw manga eyes, please enjoy! :3
First, I like to start out by drawing the top of the eye.
Now...add the bottom part of the eye ^^ DO NOT COLOR IT IN YET...please x3
Next you add the "middle" of the eye (i dont know what to call it XD) This is where all of the color will be...so i guess we could call it an iris :3
Now that you have the basic shape of your eye planned out use the fill tool to fill in each part with black on 100% trans.(you may want to erase the lines between each part so it is all just one shape)
Choose a light shadow of gray (you can also use blue) and make a medium sized line under each part of the top of your eye.
Choose the color that you want your eye to be, on 100% transparency make a shape that is similar to the middle part of your eye but leave some space between the edges ^^
Next, you should choose white and set it on a low transparency probably no higher than 15, go over the edges of your gray shading to make it smoother.
Do the same thing for the solid color you chose for your eye, then on 100% transparency add a pupil.
Now, pick a lighter shade of the basic color of your eye. Using the pencil tool make a u shape on the bottom of the eye, keep making smaller u shapes using a lighter version of your color each time. Pick a shade of your color that is almost white and make small vertical lines.
Now you can add a few lines for the eyelid...and a few sparkles! You may also want to add so more details to your iris by choosing bright versions of your color and making more vertical lines. Oh yeah, MAKE SURE YOU ARE USING LOW TRANPARENSY WHEN YOU COLOR THE IRIS *sorry, i forgot to tell u that in step 9 >.<')
Add an eyebrow :D