Sensory retina

This image shows the elegant structural organization of the retina, which embryologically is a part of the central nervous system.  Functionally, the retina consists of a three-cell pathway: photoreceptors (rods and cones), bipolar cells and ganglion cells.  Neural integration between these layers occurs in two synaptic regions, the outer plexiform layer and the inner plexiform layer.  The vitreous chamber is visible in the upper left, the choroid is visible in the lower right.  400x

The pigment epithelium is the outermost layer of the retina and is non-visual.  It consists of a simple cuboidal epithelium with cells containing melanin to absorb stray light and prevent reflection.

Rods and cones are photoreceptors that form the photoreceptor layer.  These cells transduce light energy into neural activity.

Bipolar cells synapse with rods and cones as well as ganglion cells.

Ganglion cells, located in the ganglion cell layer, synapse with bipolar cells and their cell bodies.  Axons from these cells travel in the nerve fiber layer, passing toward the optic disc, where they exit as the optic nerve.

Ganglion cells, located in the ganglion cell layer, synapse with bipolar cells and their cell bodies.  Axons from these cells travel in nerve fiber layer, passing toward the optic disc, where they exit as the optic nerve.

The outer plexiform layer is the location of synapses of rods and cones with bipolar cells.

The inner plexiform layer is the location of synapses of bipolar cells and ganglion cells.

The vitreous chamber is visible in the upper left.

The choroid is visible in the lower right.  The choroid layer, which is pigmented and highly vascular, forms part of the vascular tunic, along with the ciliary body and the iris.

In most areas of the retina, light must pass through the entire retina to reach the photoreceptors (rods and cones), where it is transduced into neural signals.  In the region of the retina with greatest visual acuity, the fovea, the bipolar and ganglion cells are displaced laterally, allowing light to directly reach the photoreceptors.

Visual signals originate in the photoreceptors and are transmitted in the opposite direction from the light path, i.e., from photoreceptors to bipolar cells to ganglion cells.  Visual integration occurs along this pathway before reaching the ganglion cells, whose axons transmit visual signals to the brain through the optic nerve.

Image taken of a slide from the University of New England College of Osteopathic Medicine collection.  The slide was produced by Dr. Allen Bell.