The visual pathway/visual system is the part of central nervous system which gives organisms the ability to process visual detail , as well as enabling the formation of several non-image photo response functions. It detects interprets information from visible light to build a representation of the surrounding environment . The visual system carries out a number of complex tasks , including the reception of light and the formation of monocular representations; the buildup of a nuclear binocular perception from a pair of two dimensional projections ; the identification and categorization of visual objects ; assessing distances to and between objects and guiding body movements in relation to the objects seen.

1. VISUAL PATHWAY/VISUAL SYSTEM
Md . Azizul Islam
Associate Optometrist
Oculoplasty Department ( IIEI&H )
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2. DEFINITION
The visual pathway/visual system is the part of central nervous system
which gives organisms the ability to process visual detail , as well as
enabling the formation of several non-image photo response functions. It
detects interprets information from visible light to build a representation
of the surrounding environment . The visual system carries out a number
of complex tasks , including the reception of light and the formation of
monocular representations; the buildup of a nuclear binocular perception
from a pair of two dimensional projections ; the identification and
categorization of visual objects ; assessing distances to and between
objects and guiding body movements in relation to the objects seen .
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3. Visual Pathway
The visual system includes the eyes, the connecting pathways through
the visual cortex and other parts of the brain .(Anatomical Terminology)
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4. Overview of Visual Pathway
Mechanical: Together the cornea and lens refract light into a small image
and shine it upon the Retina . The Retina transduces this image into
electrical pulses using rods and cons. The optic nerve than carries these
pulses through the optic canal . Upon reaching the optic chaisma the
nerve fibres decussate. The fibres then branch and terminate in three
places .
Neural: End in lateral geniculate nucleus . Before the LGN forwards the
pulses to primary visual cortex and it gauges the range of objects and
tags every major object with a velocity tag. These tags predict object
movement .
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5. Structure of Visual System
 The eye, especially the retina
 The optic nerve
 The optic chaisma
 The optic tract
 The lateral geniculate body
 The optic radiation
 The visual cortex
 The visual association cortex.
Visual pathway divided into anterior (structure
involved in vision before LGN) posterior (after LGN)
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6. EYES & RETINA
EYE: Light entering the eye is refracted as it passes through the cornea.
Light then passes through the pupil( Regulating by Irish ) and is further
refracted by the lens. The cornea and lens act together as a compound
lens to project an inverted image onto retina.
RETINA :The retina is the nerve layer that lines the back of the eye,
senses light, and creates impulses that travel through the optic nerve to
the brain. There is a small area, called the macula, in the retina that
contains special light-sensitive cells. The macula allows us to see fine
details clearly.
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7. Retina
The retina consists of a large number of photoreceptor cells which
contain particular molecules called opsins. In human two types of
opsins are involved conscious vision : rod opsins,cone opsins and newly
invented some of retinal ganglion cells layer.
Rods and cones are differ in function . Rods are found primarily in the
periphery of the retina and help to see at low levels of light and night
vision . Cones are found primarily in the centre (fovea )
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8. Retina
Of the retina. There are three types of cones that differ in the
wavelength of light they absorb ; they are usually called short or blue ,
middle or green and long or red. Cones are help to distinguish colour
and bright light and normal light vision . Ganglion cell layer has some
photoreceptive property. It has also role in conscious and unconscious
visual perception .
(There are two pathways for sight in the retina -one is classic
photoreceptor (rods and cones ) and other photorective ganglion
cells which act as rudimentary visual brightness detectors .
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9. Retinal Function
 The retina processes light through a layer of photoreceptor
cells and formed a picture from the focussed light .
 Detecting the quality such as colour and light-intensity .
 Retina gathered information by photoreceptor cells and
send information to brain via optic nerve .
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10. Optic Nerve
The optic nerve is located in the back of the eye. It is also called the
second cranial nerve or cranial nerve II. It is the second of several
pairs of cranial nerves.
Anatomical Structure :The optic nerve is made of ganglionic cells or
nerve cells. It consists of over one million nerve fibers. Our blind
spot is caused by the absence of specialized photosensitive (light-
sensitive) cells, or photoreceptors, in the part of the retina where
the optic nerve.
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11. Optic Nerve
Although the optic nerve is part of the eye, it is
considered part of the central nervous system.
Parts of Optic Nerve - it is about 47-50mm in
length . It divided in four part .
Part…….
a. Intraocular-1mm
b. Intraorbital-30mm
c. Intracanalicular-6-9mm
d. Intracaranial-10mm
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12. The left optic nerve and the optic
tracts…..
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13. Optic Nerve
Function:
 Transmit the visual information from the retina
to visual centres of the brain as electrical
impulses .
 Help to control eye movement and motor
response.
 Help in conscious and unconscious vision.
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14. Optic Chaisma
A decussation or X-shaped crossing.
optic chiasm a structure in the forebrain formed by the decussation
of fibers of the optic nerve from each half of each retina and optic
nerve at the base of the hypothalamus of brain.
Function : The information coming from both eyes is combined and
then splits according to the visual field. The corresponding halves of
the field of view (decussate :right becomes left) are sent to the left
and right halves of the brain, respectively to be processed. That is
the right side of primary visual cortex deals with the left half of the
field of view from both eyes and similarly for the left brain.
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15. The anatomical course of the optic
nerve, optic chaisma and optic tract…
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16. Optic Tract
The optic tract is an extension of the optic nerve located in the brain. It
begins at the area where information from the left eye and right eye
cross (or “decussate”) to create a complete visual picture.
Anatomical structure : The optic tract is actually comprised of two
separate tracts: the left optic tract and the right optic tract. The left
optic tract transfers information from temporal retinal fibers from the
left eye and nasal retinal fiber from the right eye. The right optic tract
transfers information from the temporal retinal fibers from the right eye
and nasal retinal fibers from the left eye.
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17. Optic Tract
Function : Cover different part of visual field
and help to formed a complete image. Also
regulate the papillary light and Dark reflexes.
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18. Lateral Geniculate body/Nucleus
The lateral geniculate nucleus (LGN; also called the lateral
geniculate body or lateral geniculate complex) is a relay center
in the thalamus for the visual pathway. It receives a major
sensory input from the retina. The LGN is the main central
connection for the optic nerve to the occipital lobe. In humans,
each LGN has six layers of neurons (grey matter) alternating
with optic fibers (white matter) In human and other primates.
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19. Lateral Geniculate body/Nucleus
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20. Mechanism
Layers 1, 4, and 6 correspond to information from the contralateral
(crossed) fibers of the nasal retina (temporal visual field); layers 2, 3,
and 5 correspond to information from the ipsilateral (uncrossed)
fibers of the temporal retina (nasal visual field). Layer one (1) contains
M cells which correspond to the M (magnocellular) cells of the optic
nerve of the opposite eye and are concerned with depth or motion.
Layers four and six (4 & 6) of the LGN also connect to the opposite
eye, but to the P cells (color and edges) of the optic nerve. By
contrast, layers two, three and five (2, 3, & 5) of the LGN connect to
the M cells and P (parvocellular) cells of the optic nerve for the same
side of the brain as its respective LGN.
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21. Function of LGN
The functions of the LGN are multiple. Its unique folding contributes to its
utility by performing a range of anatomical calculations without requiring
mathematical computations. These include both temporal
correlations/decorrelations as well as spatial correlations And also…..
 Help to vergence and converge the eyes relating to object.
 Control the focus and calculate the distance.
 Help to formed a larger stereoscopic mapping of the visual field.
 Help to predict the velocity of object and control the body movement
relating to object.
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22. Optic Radiation
The optic radiation (or geniculocalcarine tract) is part of the visual
pathway, forming the connection between the lateral geniculate
nucleus of the pulvinar of the thalamus with the primary visual
cortex of the occipital lobe.
Anatomy :Anatomically, the optic radiations resemble a flattened
sheet of white matter. From their origin at the lateral geniculate
nucleus, the optic radiations pass through the retrolentiform part
of the internal capsule and spread out into three main bundles:
 Anterior bundle (Meyer’s loop)
 Central bundle
 Posterior bundle (Baum’s loop)
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23. Visual System
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24. Function of OR
The optic radiation, One on each
side of brain, carry information
from the thalamic lateral geniculate
nucleus to visual cortex.
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25. Visual Cortex
The visual cortex is a part of the brain that allows vision. It is
relatively thin – between 1.5mm and 2mm in humans. In
monkeys and apes the visual cortex take up much of their
brain. Physically, the visual cortex is at the back of the brain in
the occipital lobe. The region that received information
directly from LGN is called primary visual cortex. Primary
visual cortex is the best studied area of visual cortex. Primary
visual cortex sends information to two pathways called ventral
stream and Dorsal stream. Each LGN gets signals from the
opposite visual field.
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26. Visual Cortex
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27. Function
The visual cortex is the largest system in the brain and is responsible
for processing the visual image.
 Received signals from both eyes alternatively.
 Work as edge detectors, motion detectors, stereoscopic death
detectors and colour detectors.
 Recognition and representation of object location, controls eyes
and arm's, especially when visual information is used to guide eye
and body movement.
 Visual cortex is also associated with the storage of long term
memory.
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28. Visual Association Cortex
Association cortex is the cerebral cortex outside the
primary areas. It is essential for mental functions that
are more complex than detecting basic dimensions of
sensory stimulation, for which primary sensory areas
appear to be necessary. In humans the association
areas are by far the most developed part of the
cerebral cortex, and the brain in general. These areas
are necessary for perceptual activities, like recognizing
objects (toasters, horses, trees, words, etc), rather than
simple contours, edges or sensory qualities like color
or pitch.
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29. References
 Comprehensive Ophthalmology, 4th Edition, by A. K. Khurana
 Kanski's Clinical Ophthalmology,7th Edition by Jack Kanski
 Picture+Vedio : Google + Me
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