Final answer:
The cornea is the transparent covering of the eye, functioning as a protective barrier and focusing element for light entering the eye.
Step-by-step explanation:
The cornea is the transparent covering of the eye, serving as a barrier between the inner eye and the outside world, and plays a crucial role in focusing light waves that enter the eye.
The outermost layer of the eye, known as the fibrous tunic, consists of the sclera and the cornea. The sclera forms the majority of the eye's surface and is predominantly not visible. The cornea, being transparent, covers the anterior tip of the eye, permitting light to enter. Within the middle layer, the vascular tunic, there are structures like the choroid which is highly vascularized, supplying the eye with blood, and the ciliary body, which attaches to the lens and aids in focusing light onto the retina. The iris, part of the vascular tunic, controls the pupil's size and thus regulates the amount of light entering the eye. The inner layer, or the neural tunic, contains the retina responsible for photoreception.