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Rod photoreceptors These neurons contain pigments which are sensitive to low levels of light. Once exposed to light, a chemical reaction occurs inside the cell that causes the neuron to fire an action potential which is propagated to connecting neurons and will eventually reach the visual centre of the brain. Choroidal blood vessels The choroid consists of a dense network of capillaries which deliver oxygen & nutrients via the blood to the RPE and photoreceptors. These vessels have a special perforated structure which allow small molecules and proteins to easily get in & out through pores. Horizontal cells These neurons help to collect information from the photoreceptors which is then passed on to the bipolar cells. Their shape is not a ‘classical’ neuron shape but they are still able to transmit electrical signals. Cone photoreceptors Like rod photoreceptors, these cells detect light. There are three types of cone photoreceptors, each of which are sensitive to different wavelengths of light which enables us to distinguish between different colours. Bipolar Cells These neurons are important connectors in the retina, forming synapses (a neuronal junction) with 4 different types of neurons. They are connected to the photoreceptors and the horizontal cells at one end and to amacrine and ganglion cells at the other end. They receive electrical signals from the photoreceptors and horizontal cells which they then translate before passing on to the amacrine & ganglion cells. Retinal blood vessels Due to the multilayered nature of the retina, the retinal blood vessels need to form three separate layers in order to supply all the cells in the retina with enough oxygen & nutrients to maintain healthy vision. Müller cells These are non-neuronal glial cells which support the surrounding neurons and blood vessels by secreting factors that help them survive and providing architectural structure by stretching all the way through the retina. Their endfeet form close associations with blood vessels and axons. Retinal pigment epithelium (RPE) These heavily pigmented epithelial cells help to maintain the health of the overlying neurons in the retina. The cells fit together in a hexagonal shape and interdigitate with the underlying neurons with long pigmented extensions. Amacrine cells These neurons help to transmit signals from the bipolar cells to the ganglion cells. Ganglion cells These neurons gather the information from the amacrine and bipolar cells and pass this along a very long axon that extends into the brain. This work was produced by the UCL Institute of Ophthalmology Knitting Group with help from The Scientific Workshop and friends including The Alresford WI & The Stroud Green WI, Mary Barker, Ruth Stone, Sam Black and Ellen Kelly.