The thinnest part of the sclera is located where the extraocular muscles attach to the wall of the eyeball, and is about 0.3 mm thick; since there are six extraocular muscles in each eyeball, each of which attaches to a different part of the wall of the eyeball, there are multiple thinnest points of the sclera in each eyeball. The thickness of the rest of the sclera is not exactly the same. The thickest parts of the sclera are located at the back of the eye around the optic nerve and at the angle scleral rim at the junction of the sclera and cornea, which is about 1mm thick. The sclera is milky white and opaque, and together with the transparent cornea in front of it, it forms the outermost layer of the wall of the eyeball, which protects the tissues inside the eye and maintains the shape of the eyeball.