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Portrait of Retina

Anatomy · Eye, ear & senses

Retina

The light-sensitive lining of the back of the eye

Eye · inner coat

The thin, multilayered sheet of neural tissue that lines the inside of the back of the eye, between the vitreous body and the vascular choroid. Only about half a millimetre thick, it contains the photoreceptors and the first stages of processing, and its ganglion-cell axons gather to leave as the optic nerve. It is developmentally part of the brain.

How to spot them

  • ▸A thin, transparent sheet lining the back two-thirds of the inside of the eyeball, ending in a scalloped edge behind the ciliary body
  • ▸Ten layers, the light-sensitive cells lying at the back, furthest from the incoming light
  • ▸Underlain by a single layer of pigmented cells and the blood-rich choroid
  • ▸The part of the central nervous system a doctor can see directly with an ophthalmoscope

What to know

Ten histological layers, with the light-sensitive cells at the very back, behind the nerve cells that carry their signals

The retina — light must pass through the ganglion and bipolar cell layers to reach the photoreceptors

Its serrated front margin lies behind the ciliary body, where the light-sensitive part ends

The ora serrata of the retina

Supplied twice: the inner layers by a central artery, the outer layers diffusing from the choroid

The retina and its dual blood supply (the central retinal artery from the ophthalmic artery)

A pigmented layer on its outer surface soaks up stray light and recycles the visual pigments

The retinal pigment epithelium

Flashes, a shower of floaters and then a curtain falling across vision as its neural layer peels from the pigmented layer beneath

Retinal detachment, a surgical emergency

An outgrowth of the embryonic diencephalon, the only piece of the central nervous system visible in a living person

The retina, derived from the optic cup

Photographed every year in people with diabetes to catch leaking and bleeding vessels before sight is lost

Diabetic retinopathy screening of the retina

Key ideas

  • The retina is wired 'back to front': the photoreceptors face away from the light and the ganglion cell axons run across the surface, which is why the optic disc makes a blind spot.
  • It is not a passive film. Horizontal, bipolar and amacrine cells begin the processing of contrast and movement before any signal reaches the brain.

Quick-fire facts

  • •Its ten layers, from the vitreous side: inner limiting membrane, nerve fibre layer, ganglion cell layer, inner plexiform, inner nuclear, outer plexiform, outer nuclear, outer limiting membrane, photoreceptor layer, retinal pigment epithelium
  • •Around 1.2 million ganglion cell axons form the optic nerve
  • •Roughly 90–120 million rods and 4.5–6 million cones (estimates differ by source)
  • •Only about 0.2–0.5 mm thick, thinnest at the fovea
  • •The neural retina and the pigment epithelium derive from the inner and outer layers of the optic cup
  • •The central retinal artery, a branch of the ophthalmic artery, enters the eye within the optic nerve; blockage causes sudden painless loss of vision
  • •The ophthalmoscope, introduced by Hermann von Helmholtz in 1851, allowed the retina to be seen in a living patient
  • •Santiago Ramon y Cajal's drawings of retinal cell layers helped him share the 1906 Nobel Prize in Physiology or Medicine

Drill it — 7 cards

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Sources