Pupil

The opening in its centre is the pupil, through which light enters. Behind the pupil, the transparent lens changes shape to bring light into focus on the retina.

The hole in its centre is the pupil. Light passes through this opening; the pupil is not itself a tissue or muscle.

At its centre is the pupil. The pupil is not a piece of tissue: it is a hole through which light passes. Muscles in the iris alter the pupil's diameter, controlling how much light enters.

The cornea bends, or refracts, the light. It then passes through the pupil, an opening in the coloured iris, and through the transparent lens. The cornea and lens bring rays from each point on the object together on the retina at the back of the eye.