1. Central visual pathways
Domina Petric, MD

2. Introduction
The ganglion cell axons from the nasal retina go via the medial part of the optic nerve and cross the midline to project in contralateral targets in diencephalon and midbrain.
The ganglion cell axons from the temporal retina go via the lateral part of the optic nerve and remain on the ipsilateral side of the brain.
Lateral geniculate nucleus is a target where ganglion cell axons synapse and from there rise the optic radiations.
Optic radiations go around the lateral ventricle to supply upper and lower parts of the calcarine sulcus where is the primary visual cortex.

3. The ganglion cell axons from the nasal retina
cross the midline in optic chiasm.
The ganglion cell
axons from the
temporal retina
stay ipsilateral.
From the other eye...
Optic chiasm
Synapse in ipsilateral
lateral geniculate nucleus.
Synapse in contralateral
lateral geniculate nucleus.

4. Suprachiasmatic nucleus of hypothalamus
It has a molecular clock.
This nucleus is master generator of circadian rhythms for the body.
Recieves an input from special set of retinal ganglion cells that have their own opsin protein.
This input is very important for regulation of circadian rhythm because it provides information about daytime/nightime changes.

5. Pretectum (pretectal nuclei)
reflex control of pupil and lens
controll over eye accommodation

6. Pupillary light reflex
Pretectum in one side of the midline is getting input derived from both retinas: ipsilateral eye temporal parts of retina and contralateral eye nasal parts of retina.
This is the sensory (afferent) limb.
The motor (efferent) limb arises out of the pretectum.
Pretectum in one side gives rise to the axons that are directed to both sides of the midline.

7. Pupillary light reflex
Target is the Edinger-Westphal nucleus of the third cranial nerve.
From EW nucleus axons grow through the third nerve and synapse with a postganglionic neuron in ciliary ganglion.
Postganglionic axons provide parasympathetic innervation of the constrictor muscle of the iris.
Signal from the EW nucleus remains ipsilateral.

8. Pupillary light reflex
Pretectum in one side gives rise to the axons that are directed to both sides of the midline.
Because of the bilateral pretectal representation to the EW nucleus, both pupils constrict if only one eye is exposed to the light.

9. orientation of movements of the eyes and head
Superior colliculus
orientation of movements of the eyes and head

10. Image is inverted and left-right reversed.
Visuotopy
Image is inverted and left-right reversed.

11. Left eye Temporal parts of the retina catch a nasal part of the
picture.
Nasal parts of the retina
catch a temporal part of
the picture.
Left eye

12. Lower parts of the retina catch the upper part of the picture.
Upper parts of the retina catch the lower part of the picture.

13. Left visual field is seen
with the nasal part of the left eye retina
and the temporal part of the right eye retina.
Right visual field is seen with the nasal part
of the right eye retina and the temporal part of
the left eye retina.

14. Optic chiasm
Axons from nasal parts of the both retinas cross the midline in the optic chiasm.
About 55% of axons in the optic nerve are derived from nasal part of retina and cross the midline.
Remaning 45% of axons in the optic nerve are derived from temporal part of retina.
Left optic tract behind the optic chiasm visualises the right side of visual space.
Right optic tract behind the optic chiasm visualises the left side of visual space.

15. Optic radiation
From the lateral geniculate nucleus axons grow around the lateral ventricle as optic radiation and run posterior in the white matter towards the occipital lobe.
Axons of the optic radiation that are sweeping in the dorsal and posterior direction, around the atrium of the lateral ventricle, terminate on the posterior back of the calcarine sulcus in the cuneus gyrus.
Those fibers are representing the superior retinal quadrants for inferior visual field.

16. Optic radiation
Axons of the optic radiation that are sweeping down into the temporal lobe and then around lateral aspect of the temporal horn of the lateral ventricle, terminate on the lower bank of the calcarine sulcus and innervate cortex of the lingual gyrus.
This is the Meyer´s loop (temporal portion of the optic radiation).
Those fibers are representing the inferior retinal quadrants for superior visual field.

17. A B http://casemed.case.edu
Optic radiation: A) fibers that end up into the cuneus gyrus are from superior retinal quadrants for INFERIOR visual fields B) fibers that end up into the lingual gyrus (Meyer´s loop) are from inferior retinal quadrants for SUPERIOR visual fields B

18. Calcarine sulcus
It is formed by the folding of the cuneus and lingual gyrus.
Cuneus (wedge) gyrus
Cuneus gyrus is representing the lower
part of the visual field.
Calcarine sulcus
Lingual gyrus
Lingual gyrus is representing the upper
part of the visual field.

19. Extrastriate visual cortex
Those are rings of higher order visual areas.
MT plus region is rich of motion sensitive cells (spatial analysis) and it is part of dorsal processing stream.
Dorsal processing stream is concerned with spatial analysis and answers the question WHERE am I looking at?
Dorsal processing stream goes towards the parietal lobe.
Ventral processing stream adresses the question WHAT or WHO am I looking at?
Ventral processing stream goes towards the temporal lobe.

20. http://sciencewise.anu.edu.au Parvocellular pathway is
Magnocellular pathway is
the dorsal processing stream or WHERE pathway.
Parvocellular pathway is
the ventral processing stream or
WHAT (WHO) pathway.

21. Visual field deficits

22. Large area of blindness in one eye or a visual field.
Anopsia
Large area of blindness in one eye or a visual field.

23. Blindness in one visual hemifield seen by an eye.
Hemianopsia
Blindness in one visual hemifield seen by an eye.

24. Blindness in one quadrant of a visual hemifield seen by an eye.
Quadrantanopsia
Blindness in one quadrant of a visual hemifield seen by an eye.

25. Small area of blindness in a visual field (blindspot).
Scotoma
Small area of blindness in a visual field (blindspot).

26. A: lesion of the optic nerve before the optic chiasm leads
to ipsilateral anopsia (one eye blindness).
B: lesion in the middle of the optic chiasm (pituitary tumour)
leads to heteronymous hemianopsia (temporal visual fields
deficits in both eyes).
C: lesion of the optic tract after the optic chiasm leads
to homonymous hemianopsia (ipsilateral eye nasal field
deficit and contralateral eye temporal visual field deficit).
Neuroscience, 5th Edition. Sinauer Associates, Inc

27. D: if there is damage of optic radiation that ends up
into the lingual gyrus (Meyer´s loop), there will be
contralateral upper homonymous quadrantopsia.
E: if there is extensive damage of the visual cortex,
there will be contralateral homonymous hemianopsia
with macular sparing.
Macular sparing
Neuroscience, 5th Edition. Sinauer Associates, Inc

28. there will be contralateral homonymous inferior quadrantopsia.
F: if there is damage to the optic radiation that ends up in the cuneus gyrus,
there will be contralateral homonymous inferior quadrantopsia.

29. Rarely, there can be damage of lateral parts
of the optic chiasm with nasal visual fields
deficits in both eyes.
Wikipedia.org

30. Literature
neuroscience: Leonard E. White, PhD, Duke University
Neuroscience, 5th Edition. Sinauer Associates, Inc
Wikipedia.org