The external eye has upper and lower lids which close over the globe to protect it. The sclera is the white of the eye, the colored portion is the iris, and the black opening in the middle of the iris is a hole known as the pupil. This is the only window in the body through which the nervous system can be seen directly.
The anterior transparent media consists of the cornea, anterior chamber and lens; the posterior elements of the globe are covered with specialized nerve tissue, the retina.
The optic nerve enters the eye posteriorly along with its own blood supply; this area is known as the optic disc. The macular area is where visual acuity is greatest.