1. Ákos Lukáts MD. PhD. (lukats.akos@med.semmelweis-univ.hu)
The Visual Pathway
Ákos Lukáts MD. PhD.

3. The Optic Part of the Retina: Major Cell-types
choroid
PHOTORECEPTORS (I)
outer synaptic zone
BIPOLAR CELLS (II)
inner synaptic zone
GANGLION CELLS (III)
optic nerve fibers
Vitreous body
EXCITATION

4. Blind spot: optic nerve head – starting point of the optic nerve, containing the axons of ganglion cells

5. Visual Pathway: Anatomy
optic chiasm
optic nerve (II)
optic tract
lateral geniculate body
(CGL)
optic radiation
primary visual cortex

6. Optic Chiasm: Partial Crossing
The eye will project an upside-down smaller image on the retina – the nasal visual field projects to the temporal retina.
The fibers coming from the nasal part of the retina (temporal visual field) cross in the optic chiasm.
Final result:
The image of an object in the right visual field (C) is projected to the left optic tract, CGL and visual cortex. The cortex can compare the images of the object coming from both sides.

7. The fibers of the nasal retina cross over in the optic chiasma
Temp.
Nas.
Temp.
Nas.
The visual pathway
left
right
The fibers of the nasal retina cross over in the optic chiasma
The right lateral geniculate body (CGL) receives inputs from the contralateral (left) visual fields of both eyes
The fibers of the temporal retina stay on the same side

8. bal jobb Temp. Nas. Nas. Temp.
No further crossing of fibers occur after the CGL till the primary visual cortex (except for foveal fibers!)

9. P P MM
The visual pathway
Ganglion cell axons give off collaterals to the midbrain before arriving at the CGL (light reflex-afferents)
Some macular fibers leave the optic radiation after the CGL and cross over

10. Optic Radiation: projections
CGL
calcarine sulcus
Meyer’s loop (fibers from the inferior retina reach the cortex through a loop in the temporal lobe

11. Visual Field Losses I. A. Right anopsia (amaurosis)
B. Bitemporal hemianopsia
C. Homonym hemianopsia
D. Homonym hemianopsia
+ macular sparing

12. nucl Edinger-Westphal
Pupil Reflex
Illumination of any eye will result in contraction of both pupil. (Automatic shutter)
Sensory part:. Optic n. (collaterals before LGB).
Central processing: midbrain, pretectal nuclei.
Motor part: m. sphincter pupillae - parasympathetic innervations (n. III, accessory oculomotor (Edinger-Westphal) nucleus, ciliary ggl.).
Antagonist: m. dilatator pupillae (sympathetic innervations, sup. cervical ggl).
n. III.
ggl. ciliare
pretectalis nuclei
nucl Edinger-Westphal
ggl. cervicale sup.

13. Visual Field Losses II.
A: no pupil contraction on light reaching the right eye, but both pupils contract to illumination of the left eye
A. Right anopsia (amaurosis)
B. Bitemporal hemianopsia
C. Homonym hemianopsia
D, E: no change in the reflexes of the pupil
D. Homonym hemianopsia
+ macular sparing
B, C: no reflex evoked if the damaged retinal half can be illuminated selectively – impossible without special devices – with normal pupil lamp, the change usually remains undetectable, as both pupils contract

14. Damage of the Motor Part of the Pupil Reflex
n. III.
Illumination of any of the eyes will result in pupil contraction of only one eye. No contraction on the site of the damage.
Cause: damage of the motor part of the reflex (mostly of n. III – eg: in case of increased intracranial pressure).
No visual field loss, but other symptoms of oculomotor nerve damage could be visible (eye deviates laterally and inferiorly, ptosis, double image possible, accommodation (focusing) problems.
ggl. ciliare
pretectalis nuclei
nucl Edinger-Westphal
ggl. cervicale sup.

15. Other Sidebranches… Pretectal region Pupil reflex Retina
coordination of eye movements
Superior colliculus
90%
Hypothalamus, suprachiasmatic nucl
circadian, circaannual rhythms
CGL
Primary visual cortex (V1, Brodmann 17, area striata)

16. A BIT OF FUNCTION

17. CGL Binocular zone of right hemiretina
Left lateral geniculate body: receives inputs from the contralateral visual fields of both eyes
Each layer receives inputs from one eye only
Inputs from each eye remain segregated
I = Ipsilateral (temporal) 2, 3, 5
CGL
C = Contralateral (nasal) 1, 4, 6
2 ventral -Magnocellular pathway (M channel – where?)
4 dorsal -Parvocellular pathway (P channel – what?)

18. Primary Visual Cortex Input from the superior retina
(inferior visual field!)
cuneus
sulcus
calcarinus
occipital pole
superior
macular
inferior
foveal fibers have disproportionately high representation
macular
gyrus
lingualis
Input from the inferior retina
(superior visual field!)
occipital lobe
(medial surface)

19. Ipsi- and contralateral projection: ocular dominance
Ocular dominance columns of the cortex

20. Orientation columns
Cells responding to a certain orientation form small groups (marked with different colors on the map).
The activity extends to the entire thickness of the cortex (columns).

21. Color-selective patches - „blobs”
cortical surface
blobs
white matter
The blobs are not orientation selective, rather they are sensitive to colors. The activity is most extensive in the cortical layers 2-3 of tangential cortical sections.

22. Module: functional unit of the primary visual cortex.
The module is a hypercolumn of cca. 1 mm2 surface area of cortex
- in which a unit area of the visual field is reflected,
- in which all orientation selective columns, both ocular dominance-columns and the respective color-sensitive blobs are present.
The modules exhibit a strict retinotopic distribution pattern in the primary visual cortex.

23. Visual Cortex 3. Area peristriata (19 or V4-5)
2. Area parastriata (18 or V2-3)
1. Area striata (17 or V1)

25. Functional topography of the visual cortex
V1 – primary visual cortex (all functions)
V2 – secondary visual cortex (all functions)
V3 – secondary visual cortex (recognition of form)
V4 – tertiary visual cortex (recognition of color)
V5 – tertiary visual cortex (recognition of movement)

26. Illusions

27. Outline and Contrast Recognition Enhancement

28. 3D processing

31. Image - Background

34. Previous experiences

35. So? What do we see actually?

36. Literature
Ross MH. Histology. A Text and Atlas (Lippincott Williams and Wilkins, Philadelphia, 2003)
Moore KL, Dalley AF. Clinically Oriented Anatomy (Lippincott Williams and Wilkins, Philadelphia, 1999)
Oyster CW. The Human Eye (Sinauer Associates, Inc. (Sunderland, Massachusetts, 1999)
Wright KW. Textbook of Ophthalmology (Williams and Wilkins, Baltimore, 1997)
Carlson BM. Human Embryology and Developmental Biology (Mosby, Philadelphia, 2004)
Kandel ER, Schwartz JH, Jessell TM. Principles of Neural Science (McGraw Hill, New York, 2000)
Purves D. et al: Neuroscience, 3rd ed. Sinauer Associates, Inc, 2004
Illusions / stereograms - other examples, explanations: