Disclaimer: This is just a step-by-step explanation of how I've been doing this, I take no responsibility for anything that may go wrong during this process. If your printer gets jammed or your iron melts the paper it's not my fault, ok? ¯\(°_o)/¯ Be careful!
I really hope this all makes sense. For the record my printer is an HP Laserjet, I'm not sure exactly which other kinds of printers can successfully print to sticker paper like this. I drew the eyes using Adobe Illustrator.
I'm using this process right now to make printed eyes for Monster High dolls, but it's also useful for a whole lot of other things where you'd want this kind of accuracy and reproducibility, such as doll tattoos, customizing accessories or restoring and making custom symbols for My Little Ponies.
I recommend you make a whole lot of the transfers at once even if you only need one since it's pretty easy to ruin them in the process and it's better to have spares than to have to start again.