The visual lab

Realistic illustrations of the eye and retina, an interactive model of receptive fields and clickable maps of the visual pathways. No scores or assessments – explore for as long as it helps.

Eye and retina Visual processing From retina to cortex

The layers of the retina

Explore the cells

The retina's cells lie in different layers, but their processes meet in the plexiform layers. The visible cells are a selection from a considerably richer network.

Illustrative retinal tissue with the eye's interior at the top and brown pigment epithelium at the bottom. Blue ganglion cells are nearest the inner surface; farther out are mauve amacrine, golden bipolar and green horizontal cells. Turquoise rods have long cylindrical outer segments and coral cones taper towards the pigment epithelium. Markers identify one representative exemplar of each cell type. — Illustrative tissue reconstruction, not a micrograph or measured cell counts and proportions. Markers identify representative exemplars. The fine network and dashed cone trace illustrate principles, not verified synapses or complete connectivity. The layer list is grouped guidance, not exact image boundaries; the centre of the fovea is not shown.

Cones

Cones have tapering outer segments towards the pigment epithelium and broader synaptic endings in the outer plexiform layer. They provide the basis for colour vision and high acuity in good light. Changed glutamate release affects several types of cone bipolar cells.

Layers from the inside out

1
Nerve fiber layer
The ganglion cells' axons run along the inner surface towards the optic nerve.
2
Ganglion cell layer
The ganglion cells' cell bodies are shown here.
3
Inner plexiform layer
The ganglion cells' dendrites meet bipolar cell terminals and amacrine processes.
4
Inner nuclear layer
Bipolar, amacrine and horizontal cell bodies. Amacrine cells lie towards the inside, horizontal cells towards the outside.
5
Outer plexiform layer
The photoreceptors' synaptic endings meet bipolar and horizontal processes.
6
Outer nuclear layer
The rods' and cones' cell bodies.
7
Inner and outer segments
The inner segments lie closer to the cell bodies; the light-sensitive outer segments face the pigment epithelium.
8
Retinal pigment epithelium
Supporting cells outside the photoreceptors, next to the choroid.

Two paths, opposite directions

The light must first pass through the retina's inner layers to reach the rods' and cones' outer segments. The main flow of information is then carried back inwards through the network. When light is absorbed, the photoreceptors hyperpolarise and release less glutamate. These are graded changes, not action potentials in the rod or cone. The ganglion cells' axons, by contrast, carry action potentials out of the eye.

The rods' main pathway in dim light includes rod bipolar cells and AII amacrine cells, which relay information to the cone pathways' ON and OFF circuits. That pathway is not drawn here; the rods should therefore not be read as directly connected to the ganglion cells.

In depth: from photopigment to glutamate

When the photopigment absorbs light, a reaction chain begins that reduces the amount of cGMP. cGMP-gated ion channels close, and the photoreceptor hyperpolarises. Lower calcium inflow at the synaptic ending reduces glutamate release. The next cell's response depends on its receptors and on whether it belongs to an ON or an OFF pathway.

Sources and the figures' knowledge base

← Back to the eye Explore one cell's receptive field →Onwards: the visual pathways to cortex →

Illustrations and models for learning; not measurements.