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===The Wall (retina, uvea and sclera)===

===The Wall (retina, uvea and sclera)===

The retina is the inner layer of the eyeball, it develops from the '''optic vesicle''', which is an outgrowth of the diencephalon. It remains connected to the diencephalon via the '''{Equine Cranial Nerves - Horse Anatomy#Optic Nerve (II)|optic nerve]]'''. It can be divided into the non-visual retina (lines the back of the ciliary body) and the optic part of the retina.

The retina is the inner layer of the eyeball, it develops from the '''optic vesicle''', which is an outgrowth of the diencephalon. It remains connected to the diencephalon via the '''[[Equine Cranial Nerves - Horse Anatomy#Optic Nerve (II)|optic nerve]]'''. It can be divided into the non-visual retina (lines the back of the ciliary body) and the optic part of the retina.

The non-visual part of the retina is lined by inner and outer single-layers of epithelium; the outer layer is pigmented, the inner layer is neural. This neural inner layer contains photoreceptors, interneurons, ganglion cells and associated stromal cells, called MÜLLER cells. '''Rods''' and '''cones''' are photosensitive receptor cells, and are found in the optic part of the retina. Rods are mainly utilised at night, as they are highly sensitive receptors to black and white, while cones are mainly utilised during the day as they are used for colour vision.  The '''fovea''' is an area of the retina that contains mostly cones, and in high numbers. Here, oxygen is obtained from the choroid (a pigmented layer that makes up part of the uveal tract - mentioned further down) by diffusion. In this region, there is one nerve fibre per cone.

The non-visual part of the retina is lined by inner and outer single-layers of epithelium; the outer layer is pigmented, the inner layer is neural. This neural inner layer contains photoreceptors, interneurons, ganglion cells and associated stromal cells, called MÜLLER cells. '''Rods''' and '''cones''' are photosensitive receptor cells, and are found in the optic part of the retina. Rods are mainly utilised at night, as they are highly sensitive receptors to black and white, while cones are mainly utilised during the day as they are used for colour vision.  The '''fovea''' is an area of the retina that contains mostly cones, and in high numbers. Here, oxygen is obtained from the choroid (a pigmented layer that makes up part of the uveal tract - mentioned further down) by diffusion. In this region, there is one nerve fibre per cone.