I have a tablet now, but here's the eye tutorial that I made back when I used my mouse. I really suggest buying a tablet if you are able to though!
Eye Tutorial by Saccstry on DeviantArt
Nice poster, is not it?
This art print displays sharp, vivid images with a high degree of color accuracy on high quality canvas. A member of the versatile family of art prints, this high-quality reproduction represents the best of both worlds: quality and affordability.