11. Applied anatomy of the retina

Retinal anatomy. Back of the eye in normal conditions.

Retina= Netzhaut

• The retina is the innermost, light-sensitive "coat" of the eye
• The optics of the eye create a focused two-dimentional image of the visual world on the retina -> The retina translates that image into electrical impulses to the brain to create visual perception

Histology of Retina:

• The vertebrate retina has ten distinct layers -> From closest to farthest from the vitreous body:

1. 1) Inner limiting membrane – basement membrane elaborated by Müller cells.
2. 2) Nerve fibre layer – axons of the ganglion cell nuclei -> they become the optic nerve
3. 3) Ganglion cell layer – contains nuclei of ganglion cells
4. 4) Inner plexiform layer – contains the synapse between the bipolar cell axons and the dendrites of the ganglion and amacrine cells.
5. 5) Inner nuclear layer – contains the nuclei and surrounding cell bodies (perikarya) of the bipolar cells, amacrine cells and horizontal cells.
6. 6) Outer plexiform layer – projections of rods and cones ending in the rod spherule and cone pedicle, respectively. These make synapses with dendrites of bipolar cells. In the macular region, this is known as the Fiber layer of Henle.
7. 7) Outer nuclear layer – cell bodies of photoreceptor cells (rods and cones)
8. 8) External limiting membrane – layer that separates the inner segment portions of the photoreceptors from their cell nucleus.
9. 9) Layer of rods and cones – layer of rod cells and cone cells.

• outer segment: metabolic portions of photoreceptor cells (mitochondria, etc)
• inner segment: here the photosensitive parts of the rods and cons are located -> these parts of the cells are rich in photoreceptors!

1. 10) Retinal pigment epithelium – single layer of cuboidal cells -> This is closest to the choroid.

The vertebrate retina is inverted -> the light sensing cells are in back of the retina, so that light has to pass through layers of neurons and capillaries before it reaches the rods and cones.

The overlying neural fibre layer does not degrade vision in the inverted retina. The neurons are transparent and the accompanying glial cells have been shown to act as fibre-optic channels to transport photons directly to the photoreceptors

Macroscopic anatomy of retina

• because the retina covers the inside of the eyeball, it also has a ball-like form
• the most important macroscopic features are:

1) Optic disc (blind spot)