**2.1 Eye anatomy**

Human eye consists of many working parts such as sclera, cornea, pupil, lens, iris, ciliary body, retina, optic nerve, choroid, etc. *Sclera*, the white colored outer layer of the eye, works as a protector of the eye. *Cornea*, a transparent circular part, refracts the light entering the eye onto the lens. *Lens* is a crystalline part located directly behind the pupil. Its task is to focus light onto the retina. *Pupil* is the dark spot at the center of a healthy iris. It acts as the shutter of a camera since the amount of light entering the human eye is regulated by the diameter of the pupil. *Iris* is the colored, visible part of the eye located in front of the lens. It regulates the amount of light entering the eye by widening (dilation) and narrowing (constriction) of the pupil. *Ciliary body* delivers oxygen and nutrients to the lens and cornea. It contains the ciliary muscle, which changes the shape of the lens when our eyes focus on an object. *Optic nerve* transfers all the visual information from the retina to the brain. *Choroid* is a thin vascular layer between the retina and the sclera. It provides oxygen and nourishment to the outer layers of the retina. It also contains a pigment that absorbs excess light (**Figure 1**) [2].
