How You See

Labeled eye diagram

Tap a part to see what it does, or press Quiz to test yourself.

Horizontal section through a right eye, seen from above, light entering from the left. Fifteen parts; labels follow the usual textbook names.

The parts, front to back

Light enters through the cornea, crosses the watery aqueous humor, passes through the pupil (the opening in the colored iris), is focused by the lens, which hangs from the ciliary body on zonule fibers, and crosses the gel of the vitreous humor to reach the retina. The retina's sharpest point is the fovea; its signals leave through the optic disc (the blind spot) as the optic nerve. Around everything are the white sclera, the blood-rich choroid and, over the visible white, the conjunctiva[1].

Layer (tunic)PartsJob
Fibrous (outer)sclera, corneashape and protection; the cornea does about two-thirds of the focusing[2]
Vascular (middle)choroid, ciliary body, irisblood supply; changing the lens's shape; controlling the pupil
Neural (inner)retina, with the fovea and optic discturning light into signals and beginning to process them[3]

About the drawing

The diagram is a horizontal section through a right eye, seen from above, with light arriving from the left. Because the nose is toward the bottom of the drawing, the optic disc appears below the fovea: it lies on the nose side of the retina. Proportions are typical of textbook diagrams, not measurements of one eye. On narrow screens the labels become numbers, keyed to the list beside the drawing. The quiz asks for the parts in a shuffled order; New order reshuffles.

Two features surprise people. The retina is inside out: light passes through its nerve fibers and neurons before reaching the rods and cones at the back[3]. And the optic disc has no photoreceptors, so every eye has a blind spot[1], which you can find with the blind spot test.

Sources

  1. J. G. Betts, K. A. Young, J. A. Wise and others (2022). Anatomy and Physiology 2e, §14.1 Sensory Perception (Vision). OpenStax, Rice University. textbook
  2. P. P. Urone and R. Hinrichs (2022). College Physics 2e, §26.1 Physics of the Eye. OpenStax, Rice University. textbook
  3. H. Kolb (2011). Simple Anatomy of the Retina (Webvision: The Organization of the Retina and Visual System). University of Utah, John Moran Eye Center. textbook