Changes

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

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

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.

[[Image:Layers of the Retina.jpg|thumb|right|200px|Layers of the Retina - Copyright David Bainbridge]]

[[Image:Layers of the Retina.jpg|thumb|right|200px|Layers of the Retina - Copyright David Bainbridge]]

Layers of the retina, from vitreous humour to choroid:

Layers of the retina, from vitreous humour to choroid:

10. Pigment cells – retinal pigmented epithelium

10. Pigment cells – retinal pigmented epithelium

 

*'''Uveal tract''': a three-part physiological and pathological unit, positioned between the sclera and the retina:

The uveal tract is a three-part physiological and pathological unit, positioned between the sclera and the retina:

1. '''''choroid''''': pigmented, highly vascular layer, containing:

1. '''''Choroid''''': pigmented, highly vascular layer, containing:

a. tapetum lucidum (inner layer, nearest retina): reflective and coloured, so increases sensitivity to poor light

a. tapetum lucidum (inner layer, nearest retina): reflective and coloured, so increases sensitivity to poor light

c. black/connective layer (outer layer, nearest sclera)

c. black/connective layer (outer layer, nearest sclera)

2. '''''ciliary body''''': produces aqueous humour and vitreous humour, and is involved in lens accommodation, as its muscle fibres stretch the lens into a flatter shape, allowing distant vision

2. '''''Ciliary body''''': produces aqueous humour and vitreous humour, and is involved in lens accommodation, as its muscle fibres stretch the lens into a flatter shape, allowing distant vision

 

*'''Sclera''': continuous with the cornea at the point of the limbus. It is similar to the cornea, except that it is vascular, and has dense, irregular, fibrous connective tissue.

3. '''''Iris''''': vascular, coloured, and contractile for pupil size

*'''Iridocorneal angle''': also called the filtration angle, this is the acute angle between the iris and the cornea, which is at the periphery of the anterior chamber of the eye. Its purpose is to drain the aqueous humour. A wider angle allows for better drainage.

The sclera is continuous with the cornea at the point of the '''limbus'''. It is similar to the cornea, except that it is vascular, and has dense, irregular, fibrous connective tissue.

===Around the Eye===

===Around the Eye===