Changes

Cone cells function better in higher intensities of light (photopic vision). Most cone cells are found concentrated in the '''fovea'''. The fovea is the region of the retina where the retinal layers are parted, allowing light to fall directly onto the cone cells. Cone cells provide greater visual acuity, as each cone synapses with a single interneuron, meaning that the visual signal is not amplified, therefore is more distinct.  Cone cells respond to light in the same way as rod cells. The only difference is that the pigment present in cone cells is '''iodopsin''', as opposed to rhodopsin. Retinene that is bound to opsin within the iodopsin is stimulated in the presence of light to undergo structural change to form trans-retinene.

Cone cells function better in higher intensities of light (photopic vision). Most cone cells are found concentrated in the '''fovea'''. The fovea is the region of the retina where the retinal layers are parted, allowing light to fall directly onto the cone cells. Cone cells provide greater visual acuity, as each cone synapses with a single interneuron, meaning that the visual signal is not amplified, therefore is more distinct.  Cone cells respond to light in the same way as rod cells. The only difference is that the pigment present in cone cells is '''iodopsin''', as opposed to rhodopsin. Retinene that is bound to opsin within the iodopsin is stimulated in the presence of light to undergo structural change to form trans-retinene.

====Eye Movements====

==Central Visual Pathways==

*Saccades: the rapid, involuntary eye movements that occur in both eyes simultaneously when changing the point of fixation. Can be up to 400°/s.

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

*Smooth pursuit movements, up to 30°/s.

The '''optic nerve''' ([[Equine Cranial Nerves - Horse Anatomy#Optic Nerve (II)|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 85-88% of fibres cross over (decussate). The optic tract (the optic nerve fibres) wraps around the cerebral peduncles of the [[Equine Brain - Horse Anatomy#Midbrain|midbrain]], where it passes into the '''lateral geniculate nucleus'''; which is part of the [[Equine Brain - Horse Anatomy#Forebrain|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 [[Equine Brain - Horse Anatomy#Forebrain|cerebral cortex]].

*Vergence, which is limited by lens accommodation.

*Vestibular, up to 30°/s - 'Nystagmus': rhythmic, oscillating motions of the eye.

 

====Determination of Distance====

*Head movement: exaggerates the parallax effect

*Vergence: the brain detects the degree to which eyes must cross.

*Overlay: determination of which objects lie in front of which.

===Autonomic Innervation of the Eye===

===Autonomic Innervation of the Eye===