visual pathway and its parts

1. Visual pathway
BY: MARYAM
SHUMAILA
FRESHTA

2. Key points
 The visual pathways;
 Anatomical considerations
 Arrangement of fibers
 Clinical implications on visual field and binocularity.

3. Optic nerve
Optic chiasma
Optic tract
Lateral geniculate body
Optic radiations
Visual cortex

4. Optic nerve
parts of optic nerve
o Intraocular (1mm)
o Intraorbital (25mm)
o Intracanalicular
o (6-9mm)
o Intracranial (10-
16mm)

5. Intraocular part
 Passes through sclera, choroid and
appears in eye as optic disc.
 Intraocular portion is of 1.5mm which
expands to 3mm just behind eye because
of myelin sheath.

6. Intraorbital part
 Extends back from eyeball to optic
formaina.
 Covered by dura, arachnoid and pia.
 Central retinal artery enters nerve on its
inferomedial aspect about 10mm behind
eyeball.
 Some fibers of superior rectus and medial
rectus are adherant to its sheath so
painfull ocular movement in retrobulbar
neuritis.

7. Intracanalicular part
 About 6-9 mm long.
 The optic nerve passes through the optic
canal surrounded by its three meningeal
sheaths.
 Close relation to sphenoid and ethmoid
sinus.

8. Intracranial part
 10-16 mm length
 Above cavernous sinus and converges
with its fellow to form chiasma
 Covered by pia only.

9. Optic chiasma
o Flattened structure measuring
12mm horizontally , 8mm
anterio-posteriorly.
o It lies over diaphragma sella
o Nerve fibers arising from nasal
halves of the two retinae
decussate at the chiasma

10. Optic tracts
 Boundles of nerve fibers running outwards and backwards from postero-lateral
aspect of optic chiasma
 Consist of temporal fibers of retina of same eye and nasal half of opposite eye
 Each optic tract end in LGB.

11. Lateral Geniculate Body
 Oval structures situated at termination of optic tract
 Each LGB consist of six layers of neurons alternating with white matter.
 Each body is split into 6 laminae
 Fibers from ipsilateral temporal retina end in lamina 2,3,5
 Contralateral nasal retina end in lamina 1,46
 These 6 lamina divide LGB into 2 portions.

13. ”
“ Functions of LGB
• Relay station to relay visual information from optic tract to visual
cortex
• To gate transmission of signals to visual cortex

14. Optic radiations
 Extend from LGB to visual cortex.
 Fibers of optic radiation spreads out fanwise to form medullary optic lamina.
 Superior fibers of radiation (which subserve inferior feild) proceed directly
posteriorly through parietal lobe.

15. Inferior fibers of radiation
(which subserve superior
field) first sweap anteriorly
in meyers loop around
anterior tip of temporal
horn of lateral ventricle
and then into temporal
lobe.

16. VISUAL CORTEX
LOCATION: LOCATED ON MEDIAL ASPECT OF OCCIPITAL LOBE.
AREAS: THERE ARE TWO MAIN AREAS.

17. VISUAL CORTEX
1. PRIMARY VISUAL CORTEX: Brodmann’s area 17.
2. SECONDRY VISUAL CORTEX: Brodmann’s area 18 and 19.
BLOOD SUPPLY: Posterior cerebral artery,middle cerebral artery.

18. VISUAL CORTEX
PRIMARY VISUAL AREA:
 Occupies the walls of calcarine sulcus,extends
onto the cortex above and below the sulcus.
 Recognised by its thinness and white line or striae in grey
matter.

19. VISUAL CORTEX
SECONDARY VISUAL AREA:
 These areas surround the primary visual area on medial and
lateral surfaces.
 These are non striate.
 Shows 6 layers.

20. VISUAL CORTEX
FUNCTIONS OF SECONDARY VISUAL CORTEX:
 Enables individual to recognize what he/she saw.
 Integrates the 2 halves of visual field.
 Controls EOM muscles for smooth pursuit of targets.