The sclera is the outer wall of the eyeball. The choroid is a layer of tissue between the sclera and the retina. The retina is the thin layer that lines the eyeball and is connected to the optic nerve. The iris is the colored part of the eye. In the center of the iris is the pupil. The iris and pupil are covered and protected by a clear cornea. Copyright 2004 American Society of Clinical Oncology. Robert Morreale/Visual Explanations, LLC.