The term 'eyeball layer' refers to the different layers of the eye. The sclera, which is the outermost layer, is a tough, white fibrous membrane that covers the entire eyeball and helps to maintain its shape. The uvea, which is the middle layer, is composed of three parts: the choroid, ciliary body, and iris. It provides nourishment to the eye and helps regulate the amount of light entering the eye. Together, these two layers form the eyeball layer and are essential for proper vision.