Changes

==Structure==

==Structure==

The eye is contained within the bony orbit of the head. The bony orbit is a cavity, comprising parts of the lacrimal bone (includes fossa for nasolacrimal duct) and the maxilla (includes caudal foramen of infraorbital canal). It is continuous with the temporal bone and the pterygopalatine fossa caudally. The bony orbit is located laterally in herbivores, but is set forward in hunting animals, that is carnivores.

The eye is contained within the bony orbit of the head. The bony orbit is a cavity, comprising parts of the lacrimal bone (includes fossa for nasolacrimal duct) and the maxilla (includes caudal foramen of infraorbital canal). It is continuous with the temporal bone and the pterygopalatine fossa caudally. The bony orbit is located laterally in herbivores, but is set forward in hunting animals, that is carnivores.

[[Image:Detailed globe.jpg|thumb|right|150px|The Globe - Copyright David Bainbridge]]

[[Image:Detailed globe.jpg|thumb|right|200px|The Globe - Copyright David Bainbridge]]

Movement of the eyeball is achieved through the contraction and relaxation of six extraocular muscles:

Movement of the eyeball is achieved through the contraction and relaxation of six extraocular muscles:

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 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 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|150px|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:

===Around the Eye===

===Around the Eye===

[[Image:Extraocular Muscles.jpg|thumb|right|150px|Extraocular Muscles - Copyright David Bainbridge]]

[[Image:Extraocular Muscles.jpg|thumb|right|200px|Extraocular Muscles - Copyright David Bainbridge]]

{| style="width:75%; height:200px" border="1"

{| style="width:75%; height:200px" border="1"

|-

|-

|}

|}

[[Image: eye gross structure.JPG |thumb|right|150px|Dissected canine eye- Copyright C. Clarkson and T.F. Fletcher, University of Minnesota]]

[[Image: eye gross structure.JPG |thumb|right|200px|Dissected canine eye- Copyright C. Clarkson and T.F. Fletcher, University of Minnesota]]

All of the extraocular muscles originate at the equator of the eyeball.

All of the extraocular muscles originate at the equator of the eyeball.

[[Image:Adnexa.jpg|thumb|right|150px|Adnexa - Copyright David Bainbridge]]

[[Image:Adnexa.jpg|thumb|right|200px|Adnexa - Copyright David Bainbridge]]

*'''Adnexa''': accessory structures of the eye, including the eyelids and the lacrimal apparatus. It contains three layers of the tear film:

*'''Adnexa''': accessory structures of the eye, including the eyelids and the lacrimal apparatus. It contains three layers of the tear film:

==Central Visual Pathways==

==Central Visual Pathways==

[[Image:Central Visual Pathway.jpg|thumb|right|150px|Central Visual Pathway - Copyright David Bainbridge]]

[[Image:Central Visual Pathway.jpg|thumb|right|200px|Central Visual Pathway - Copyright David Bainbridge]]

The optic nerve ([[Cranial Nerves - Anatomy & Physiology|CN II]]) is a paired nerve that carries visual information from the retina to the brain. The ganglion cell axons leave the retina and information passes through the optic nerve to the optic chiasm, where some nerve fibres cross over. The optic tract (the optic nerve fibres) wraps around the cerebral peduncles of the midbrain, where it passes into the lateral geniculate nucleus, which is part of the thalamus. Most of the optic tract axons synapse here, and the remaining fibres branch off and synapse in the pretectal nuclei of the superior colliculi. The integrated visual information is then passed via nerve fibres to the cerebral cortex.

The optic nerve ([[Cranial Nerves - Anatomy & Physiology|CN II]]) is a paired nerve that carries visual information from the retina to the brain. The ganglion cell axons leave the retina and information passes through the optic nerve to the optic chiasm, where some nerve fibres cross over. The optic tract (the optic nerve fibres) wraps around the cerebral peduncles of the midbrain, where it passes into the lateral geniculate nucleus, which is part of the thalamus. Most of the optic tract axons synapse here, and the remaining fibres branch off and synapse in the pretectal nuclei of the superior colliculi. The integrated visual information is then passed via nerve fibres to the cerebral cortex.

==Histology==

==Histology==

[[Image:Retina numbered.jpg|thumb|right|150px|Retina - Copyright John Bredl]]

Image:Retina numbered.jpg|Retina - John Bredl

Image:Retina of the Dog.jpg|Retina of the Dog - John Bredl

Image:Stroma.jpg|Corneal Stroma - John Bredl

Image:Developing Eye.jpg|Developing Eye - John Bredl

===Cornea:===

===Cornea:===

*The cornea has an important role in image formation, it forms a primary refractive element in the eye.

*The cornea has an important role in image formation, it forms a primary refractive element in the eye.

*Bulbar conjunctiva is lined by stratified columnar epithelium.

*Bulbar conjunctiva is lined by stratified columnar epithelium.

*Contains goblet cells.

*Contains goblet cells.

==Species Differences==

==Species Differences==