An adult eye is about one inch (or 25 mm) in diameter. It resides in an area of the skull called the orbit, which visibly reveals only one-sixth of the eye. The eyelids, eyelashes and eyebrows are ocular features that protect this exposed area of the eye from strong light, dust particles, and foreign stimuli. The outermost section, or the white part of the eye, is responsible for giving it support and shape. This is known as the sclera. A thin, mucous layer called the conjunctiva lines the inside of the eyelids and covers the exposed portion of the sclera.
The sclera connects to a clear dome-shaped layer called the cornea, which controls the amount of light that enters the eye. From the cornea, the light is passed through the pupil. The pupil is the dark opening in the centre of the iris, which is pigmented and gives the eye its colour.
Apart from its ability to generate eye colour, the iris functions as a diaphragm, which causes the pupil to expand or contract when adjusting to different light intensities: getting smaller in bright light and larger in dim light.