Increasing the contrast in Photoshop could help when performing this Illustrator technique. This subject: the eyeball. Watch this Illustrator video tutorial to learn how to vector an eyeball in CS3. Vector an aye of a model of your choice using simple techniques that will be useful, not only in vectoring eyes, but tracing techniques that are used for full face and body vectoring and vexeling.
Tutvid is a site devoted to producing tons of video tutorials for Adobe software, like Illustrator. Tutvid's Nathaniel has been designing and animating since he started using Photoshop 4.0 and Macromedia (now Adobe), and shares his self-taught knowledge in these video tutorials for free. Search for Tutvid on WonderHowTo for more helpful graphic design help.
Learn how to vector an eyeball in Adobe Illustrator CS3!