Structure of the Human Visual System

In this video, we continue our discussion of perception by learning more about how we see (i.e., more about the human visual system). We also learn what causes nearsightedness and farsightedness, and we foreshadow our next video on how we perceive color.

Sclera: The white part of the eye.

Iris: The colored part of the eye.

Pupil: A circular hole through which light enters the eye; constricts or dilates as needed, based on the amount of light available in the environment.

Lens: Structure that bends light to fine-tune an image; changes shape in a controllable process known as accommodation.

Cornea: A curved, transparent layer covering the iris and the pupil, designed to bend light to focus images on the retina; problems with the curvature of the cornea can lead to visual impairments.

Retina: A thin membrane in the back of the eye that contains sense receptor cells (rods and cones) that transduce light and send that information to parts of the brain for processing.

Fovea: The central part of the retina, responsible for visual acuity; densely packed with cones for processing detail and color.

Optic Nerve: Structure containing axons of ganglion cells that travels from the retina to the rest of the brain.

Rods: Receptor cells in charge of night vision; the fovea has no rods, which his why we see stars at night better with our peripheral vision.

Cones: Receptor cells in charge of color vision and visual acuity; they require more light than rods but give us greater detail; the fovea is densely packed with cones.

Myopia: Nearsightedness, in which light is focused in front of the retina instead of on it; caused by the cornea being too steep or the eye being too long.

Hyperopia: Farsightedness, in which light is focused behind the retina instead of on it; caused by the cornea being too flat or the eye being too short.