An illustration shows a cross-section of the eye. At the left is an image of a puppy. Lines drawn from the top and bottom of the puppy cross in the center of the eye, and an inverted image of the puppy is shown at the back of the eye. A callout from the puppy reads, 1. Light waves bouncing off an object enter your eye through the cornea, pupil, and lens.
In the illustration, the white of the eye surrounds the eyeball, with the iris at the front, and a central opening for the pupil. The callout from the iris reads, 2. Iris dilates and contracts pupil to control amount of light entering eye.
A translucent covering over the eye is labeled cornea. An elongated oval to the right of the pupil is labeled Lens. The callout reads, 3. Cornea and lens focus light waves toward the retina, bending the light and projecting an inverted image.
An inverted-C shape lines the back of the eye, labeled Retina, extending to a band at the right, labeled Optic nerve. Blood vessels are shown over the area where the optic nerve arises, labeled Optic disc. A dip in the wall of the retina is labeled Fovea.
A magnified area of the retina shows a wedge with rows of different-shaped cells. The first row is labeled Ganglion cells, and shows long threads with central beads, with the threads next to the second row of cells, labeled Bipolar cells. The bipolar cells are threads with central beads. The third row of cells is labeled Photoreceptors, and show two types of cells. Cells with a thickened end with central beads are labeled Rods, and cells with a pointed end with central beads are labeled Cones. An arrow labeled Light points to the retina side of the wedge, with a callout reading, 4. Light strikes the retina, exciting photoreceptors. Arrows show the activation of bipolar cells to the right in the illustration, and then left through the cells and into the optic nerve area. The callout reads, 5. In the retina, rods and cones fire, activating bipolar cells. This excites ganglion cells, which form the optic nerve carrying messages to the brain.