Eye (Visual Pathway)

Eye : 

Eyes are organs of the visual system. They provide animals with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and convert it into electro-chemical impulses in neurons. 

Visual Pathway / Optic pathway : 

•     Visual pathway or optic pathway is the nervous pathway that transmit the impulses from the retina visual center to the cerebral cortex. 
• In binocular vision , the light rays from the temporal half of visual field fall upon the nasal part of the corresponding retina . 
• The ray from the nasal half of visual field fall upon the temporal part of the retina . 

COURSE OF VISUAL PATHWAY : Visual pathway consists of the six components : 

1. Optic nerve.
2. Optic chismata .
3. Optic tract.
4. lateral eniculate body . 
5. optic radiations.
6. Visual cortex. 

1.Optic nerve : 

• optic nerve is formed by the axon of the ganglionic cell optic nerve leaves the through the optic disk.
• Both the fibers of nasal half part and temporal half part of retina carry the impulses from temporal half and nasal half of visual field of the same eye.

2. Optic chiasma. : 

• Medial fiber of each optic nerve cross the mid line and join the uncrossed lateral fibers of the opposite side . to from the Optic tract . This area of the optic nerve fibers is called optic chiasma. 

3.  Optic tract. : 

• Optic tract is formed by uncrossed fibers of optic nerve on the same side and crossed fibers of optic nerve from opposite side . 
• All fibers of optic tract runs backwards, outwards, towards the cerebral peduncle. 

4 . Lateral geniculate body . 

• Majority of thefibers of optic tract terminate in lateral geniculate body . Which form subcortical centere for visual sensation . 
• From here geniculocalcarine tract or optic radiation arises . this tract is the last relay of visual pathway. 
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5. Optical radiations : 

• Fibers from the lateral geniculate body pass through internal capsual and from optic radiation .
• The fibers between lateral geniculate body and visual cortex are also called geniculocalcarine fibers. 
• Optic radiations end in the visual cortex. 

6. Visual cortex :

• Primary corticalcenter for vision is called visual cortex. Which is located on the middle surface of occipital lobe .

Area of isual cortex and their functions : Three area resent in the visual cortex ,

1. Primary visual area (area 17) which is concerned with the percepton of visual impulses . 
2. Secondary visual area or visual association area (area 18 ) which is concerned with the interpretation  of visual impulses . 
3. Occipital eye field (area 190 which is concerned with the movment of eyes.