The visual pathway begins in the retina and relays visual information to the occipital cortex via several structures. Damage to different parts of this pathway can result in distinct visual field defects. Lesions of the optic nerve or chiasm cause unilateral or bilateral visual loss. Lesions of the optic tract, lateral geniculate body, or optic radiations result in homonymous hemianopia. The specific location and extent of damage determines the pattern and severity of visual field loss.

1. VISUAL PATHWAY
& LESIONS
Optom. Ankit S. Varshney
B.Optom, M.Optom, Ph.D. in Optometry(pursuing) Fellowof IACLE(Aus.), Fellowof ASCO(Mum.)
Prof. at (ShreeBharatimaiyaCollege of Optometry& Physiotherapy, Surat)
Life Member of Indian Optometric Association (IOA)
Associate Member of Association of Schools and Colleges of Optometry(ASCO)
Member of Optometry Council of India(OCI)
Educator Member of International Association of Contact lense Educators (Australia)(IACLE)
Mail id: ankitsvarshney@yahoo.com
Whatsapp no. +918155955820

2. Introduction
• Each eyeball acts as camera.
• It perceives the images & relays sensations to brain (occipital cortex) via visual pathway which
comprises:-
# RETINA
# optic nerve
# optic chiasma
# optic tract
# lateral geniculate body
# optic radiation
# visual cortex
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4. Retinal layers
• Retinal pigmented epithelium
• Layer of rods and cones
• External limiting membrane
• Outer nuclear layer
• Outer plexiform layer
• Inner nuclear layer
• Inner plexiform layer
• Layer of ganglion cells
• Nerve fibre layer
• Internal limiting membrane
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6. Retina
• Most internal layer of eye, facing the vitreous
• Converts light energy into electrical energy which is then
sent to the brain via the optic nerve
• Point of sharpest vision is in the fovea; located in the center
of the macula
• The visual impulses reach occipital cortex after 124 m sec
following retinal stimulation.
-> the central part consists CONES
which are responsible for photophic vision7/15/2020 Optom. Ankit Varshney 6

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8. Optic Nerve
• Optic nerve starts from optic disc and extends up to optic
chiasma.
• It is backward continuation of nerve fiber layer of the retina,
consists of axons of the ganglion cells.
• It doesn’t regenerate when cut bcoz it is not cover by
neurilemma
• Contains over 1 million nerve fibers…once severed cannot
be reconnected=no “eye transplant”
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9. Parts Of Optic Nerve
• Intra ocular part (1 mm)
• Intra orbital part (30 mm)
• Intra canalicular part (6-9 mm)
• Intra orbital part (10 mm)
• Diameter : 3mm in orbit & 7mm near the chiasma.
• Length : 47-50mm
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11. Optic Chiasma
• It’s a oval bridge connecting the two optic nerves and two tracks.
• Measurements :
@ horizontally - 12mm
@ anterio posteriorly – 8mm
• In chiasma nasal retinal fibers are crossed but temporal fibers are not.
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12. Optic Tract
• It extends laterally and backward from the
chiasma to the lateral geniculate body.
• Each optic track consists of temporal fibers
of the same eye and nasal fibers of the
opposite eye.
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13. Lateral Geniculate Body
• These are oval structure situated at posterior
termination of the optic tract.
• Each consists of six layers of neurons.
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14. Optic Radiation
• These extend from the LGB to the visual cortex.
• It is also called as geniculo calcerine track.
• In this the upper half is made up of upper retinal fibers and lower half is
made up of lower retinal fibers.
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15. Visual Cortex
• It is located on the medial aspect of the occipital lobe,
above and below the calcerine fissure.
• It is subdivided into two areas
1.visuosensory area
2.visuopsychic area
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18. • Message is carried down the optic nerve through pathways to occipital cortex; here vision
becomes sight
• At the optic chiasm, the nasal nerve fibers cross; temporal nerve fibers go straight back to
cortex; this arrangement impacts on visual fields
• Results in visual field losses can be predicted based on where damage located on the optic
nerve
• When damage is located anterior of the optic chiasm; it is likely there will be a cortical
component to the field loss
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21. Lesions of optic nerve
• Causes : optic atrophy, traumatic avulsion,
indirect optic neuropathy, acute optic neuritis.
• Lesions through distal part of optic nerve:
Ipsilateral blindness with abolition of direct
light reflex & consensual on opposite side.
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22. • Lesions through proximal part :
Ipsilateral blindness, contralateral hemianopia, ipsilateral
abolition of direct light reflex & consensual on opposite
side.
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23. Sagital (central) lesions of chiasma
• Causes :
Suprasellar aneurysm, pituit. Gland tumors, craniopharyngioma, suprasellar
meningioma, glioma of 3rd ventricle, 3rd ventricular dilatation due to obstructive
hydrocephalus & chronic chiasmal arachnoiditis
• Features :
There is heteronymous bitemporal hemianopia.
Bitemporal hemianopic paralysis of pupillary reflexes -> usually leads to partial
descending optic atrophy.
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24. Lateral chiasmal lesions
• Causes :
Distension of 3rd ventricle causing pressure on each side of chiasma, atheroma of carotids or
post. Communicating arteries.
• Features :
Binasal hemianopia
Binasal hemianopic paralysis of pupillary reflexes – usually lead to partial descending optic
atrophy.
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25. LESIONS OF OPTIC TRACT
Causes
• Syphilitic meningitis or gumma, tuberculosis, tumors, Aneurysms of superior cerebellar or
post. Cerebral arteries.
Features
1. Homonymous hemianopia:
Binocular visual field defects involving contralat.visual space.
Both eyes manifest partial or total visual hemifield loss opposite the side of lesion.
Such hemianopia involving same side of visual space in both eyes is ‘homonymous’
Incongruity :
May be incomplete / complete.
Incomplete hemianopia-
congruity refers to how closely the extent & pattern of field loss in one eye matches that of
the other. ( Nerve fibres originating from corresponding retinal elements are however not
closely aligned. - hence lesions are characteristically incongruous (asymmetric hemianopic
defects)
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26. 2. Wernickes hemianopic pupil
• Optic tract contain both visual & pupillomotor fibres. Visual fibres terminate in LGB but pupillary fibres
leave optic tract anterior to LGB, projecting thru brachium of superior colliculus to terminate in pretectal
nucleus -hence give rise to afferent pupillary conduction defect.
When unaffected hemiretina stimulated , light reflex will be normal & when involved hemiretina
stimulated, (i.e light shown from hemianopic side) – light reflex absent. ( Needs very fine beam of light –
because of scatter of light its difficult to elicit)
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27. 3. Optic Atrophy
• Bcoz fibres in optic tract are axons of retinal ganglion cells –
• Ipsilateral disc manifest atrophy of superior & inferior aspect of neuro
retinal rim( fibres from temporal retina)
• Contralateral disc manifest bow tie pattern of optic atrophy (nasal fibres of
retina)
4. Contralateral pyramidal signs
When optic tract lesion involve ipsilateral cerebral peduncle.
5. May be associated with contralateral 3rd nerve paralysis & ipsilateral
hemiplegia.
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28. Lesions of LGB
• Incongruous Homonymous Hemianopia (asymmetric)
with sparing of pupillary reflexes.
• May end in partial optic atropthy.
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29. Arrangement of nerve fibres
There occurs temporal rotation of fibres, thereby
• Upper retinal fibres occupy upper part of optic radiations.
• Lower retinal fibres occupy lower part of optic radiations.
• Macular fibres lie in central part of O.R separating upper retinal from lower
retinal fibres.
• Other fibres : Besides visual fibres, also contain fibres that pass from
cerebral cortex to LGB, to the superior colliculus & to occulomotor nuclei.
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30. Lesions of optic radiations
• Common causes:
Vascular occlusions, primary & secondary tumors, trauma.
• Features :
1. Anterior parietal radiations
Superior fibres of radiations which subserve inferior visual fields, proceed directly
through parietal lobe to occipital cortex.
 Contralateral homonymous inferior quadrantanopia (relatively congruous) called as
PIE ON THE FLOOR
 Associated features of parietal lobe disease : Agnosia, Visual perception difficulties
(particularly with right parietal lesions), Right-left confusion & Acalculia
(particularly with left parietal lesions)
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31. 2.Temporal radiations
Inferior fibres of O.R which subserve superior visual fields first
sweep antero-inferiorly into temporal lobe (meyer loop) around
anterior tip of temporal horn of latearl ventricle  Contralateral
homonymous superior quadrantanopia called as PIE IN THE SKY
-->Associated features -- contralateral hemisensory disturbance &
mild hemiparesis (bcoz temporal radiations pass very close to
sensory & motor fibres of internal capsule before passing
posteriorly & rejoining superior fibres).
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32. 3.Posterior radiations
• Deep in parietal lobe, O.R lie just external to trigone & occipital horn of
lateral ventricle. Lesions in this area usually cause complete homonymous
hemianopia
• Optokinetic nystagmus (OKN) – useful in localizing lesion causing isolated
homonym. hemianopia without associated neurological defects. If optomotor
pathways in posterior hemisphere are damaged, OKN response diminished
when targets are rotated towards side of lesion (i.e away from hemianopia) –
occipital lobe no longer control ipsilateral pursuit, while contralateral
hemianopia inhibits refixational saccades. This is +ve OKN sign.
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33. ( combination of homonymous hemianopia & OKN asymmetry
suggests lesion involving posterior O.R.)
4. Pupillary reactions normal as fibres of light reflex leave
optic tract to synapse in sup. Colliculi.
5. Lesions do not produce optic atrophy as first order neurons (
optic nerve fibres) synapse in LGB.
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34. Lesions of optic radiations & visual cortex.
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35. Lesions of V.C
• Causes :
Vascular lesions in territory of posterior cerebral A. (90% of isolated
homonym. Hemianopia with no neurological deficits)
Less commonly migraine, trauma, primary or metastatic tumors.
• Visual field defects :
Congruous homonymous hemianopia (usually sparing macula)  occlusion
of posterior cerebral A. which supply part of V.C (striate) where
peripheral visual fields are represented.
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36. Congruous homonymous macular defect 
lesions of tip of occipital cortex following head injury or
gun-shot injury.
• No optic atrophy. Pupillary light reflexes are normal.
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