Figure below shows the schematic diagram of the human eye. Externally the eye consists or the cornea and the iris. Cornea is a transparent membrane that protects the eye. Iris is made up of tissues that are dark in colour and are opaque to light. Iris has a small hole in the middle called the pupil.
Pupil looks darker than the iris as no light rays are reflected out of the eye.
Ciliary muscles that are either in a relaxed or in a tensed state hold the convex lens. The ciliary muscles are capable of changing the shape of the convex lens. The light rays are focused on a screen called the retina. The eye sees an object because an image of the object is formed on the retina. As expected, the image of the convex lens is always inverted.