‘The human eye’ describes the optical system of the human eye and the important role the cornea plays in image formation. The lens adjusts the optical system's power to focus on objects at different distances (accommodation) and its elasticity decreases steadily with age. Common defects are myopia, hyperopia, and astigmatism. The iris ensures maximum resolution under existing lighting conditions and the pupil's diameter is governed by the amount of light reaching the retina. The retina is an inverted receptive structure where the first two stages of image processing occur. In the centre of the retina is the fovea, a tiny region from which we derive almost all our information about colour and detail.