This article presents a discussion of the operation and optical complexities of the human eye. The optical power of the eye comes from two major components, the cornea and the crystalline lens. The cornea is a transparent, almost circular membrane. Its optical power is about 43 D, accounting for most of the optical power of the eye. The crystalline lens has an optical power of about 17 D. It is about 9-10 mm in diameter and about 4 mm at its thickest point. It is composed of thin layers, or laminae, and has a refractive index of about 1.40. Behind the lens, making up about 80% of the entire eye, is the vitreous body, which is filled with fluid called the vitreous humor.