The visual system consists of the retina, optic nerve, optic chiasm, optic tract, lateral geniculate body, optic radiation, and visual cortex. Light signals from the eyes travel through these structures. At the optic chiasm, nerve fibers from the nasal retina cross to the opposite side, while temporal fibers remain on the same side. The fibers then synapse in the lateral geniculate nucleus before projecting to the primary visual cortex via the optic radiation. Specific lesions along this pathway can cause distinct visual field defects such as homonymous hemianopia.

1. BY Muhammad Ramzan Ul Rehman Nishtar Ken 1

2. BY Muhammad Ramzan Ul Rehman Nishtar Ken
2

3. Neurophysiology of Vision
BY Muhammad Ramzan Ul Rehman Nishtar Ken
3

4. the visual system/pathway
consists of:
 the retina
 The optic nerve
 The optic chiasma
 The optic tract
 The lateral geniculate body
 The optic radiation
 The visual cortex
 The visual association cortex
BY Muhammad Ramzan Ul Rehman Nishtar Ken 4

5.  optic nerve
 axons of ganglion cells of the retina
 optic chiasm
 At optic chiasma, all fibers from the nasal halves of
the retina cross to the opposite side
 crossed fibers join fibers from the opposite
temporal retina to form the optic tracts
 These fibers synapse in the
dorsal lateral geniculate
nucleus (LGN)
 from LGN to primary visual
cortex by way of the optic
radiation (geniculocalcarine
tract)
BY Muhammad Ramzan Ul Rehman Nishtar Ken 5

6. Visual pathways to the brain
BY Muhammad Ramzan Ul Rehman Nishtar Ken 6

7. BY Muhammad Ramzan Ul Rehman Nishtar Ken
7

8. BY Muhammad Ramzan Ul Rehman Nishtar Ken 8

9.  Homonymous contralateral
hemianopia with macular
sparing.
 Macular sparing occurs
because lesion of visual
cortex don't destroy all
neurons that represent the
macula.
BY Muhammad Ramzan Ul Rehman Nishtar Ken 9

10. BY Muhammad Ramzan Ul Rehman Nishtar Ken 10

11. BY Muhammad Ramzan Ul Rehman Nishtar Ken 11

12. BITEMPORAL HEMIANOPIA
BY Muhammad Ramzan Ul Rehman Nishtar Ken 12

13. BITEMPORAL HEMIANOPIA BINASAL HEMIANOPIA
BY Muhammad Ramzan Ul Rehman Nishtar Ken 13

14. High degree of spatial fidility
 Layers II, III and V receive temporal
fibers
 Layers I, IV and VI receive nasal fibers
 Layer I & II receive Y neurons
Layerr II & VI receive X cells
BY Muhammad Ramzan Ul Rehman Nishtar Ken 14

15.  Area 17
 located in the occipital lobe in the
calcarine fissure region extending
to the pole
 large representation in visual
cortex for the macula (region for
highest visual acuity)
 receives the primary visual input
BY Muhammad Ramzan Ul Rehman Nishtar Ken 15

16. visual association
cortex (area 18, 19)
responsible for
analyzing the visual
information
area for 3 dimensional
position, gross form,
and motion
area for color analysis
BY Muhammad Ramzan Ul Rehman Nishtar Ken 16

17. suprachiasmatic nucleus of the
hypothalamus
 control of circadian rhythms??
pretectal nuclei
 pupillary light reflex
 accommodation of the lens
superior colliculus
 rapid directional movement of both eyes
BY Muhammad Ramzan Ul Rehman Nishtar Ken 17

18. BY Muhammad Ramzan Ul Rehman Nishtar Ken 18

19.  The eye is innervated by both
parasympathetic and sympathetic neurons.
 Parasympathetic fibers arise in the Edinger-
Westphal nucleus, pass in the 3rd cranial
nerve to the ciliary ganglion.
 Postganglionic fibers excite the ciliary muscle and
sphincter of the iris.
 Sympathetic fibers originate in the
intermediolateral horn cells of the superior
cervical ganglion.
 Postganglionic fibers spread along the corotid artery and eventually innervate
the radial fibers of the iris.
BY Muhammad Ramzan Ul Rehman Nishtar Ken 19

20.  If a light is shone directly into one eye, its pupil constricts. This response is
known as the direct pupillary response.
 The pupil of the other eye also constricts, and this is known as the
consensual response.
BY Muhammad Ramzan Ul Rehman Nishtar Ken 20

21. BY Muhammad Ramzan Ul Rehman Nishtar Ken 21

22. Fig. 16.07
BY Muhammad Ramzan Ul Rehman Nishtar Ken 22

23.  When the amount of light entering
the eyes increases, the pupils
constrict.
 Functions to help the eye adapt
extremely rapidly to changing light
conditions.
 Direct light reflex: same pupil
constricts
 indirect (consensual) light reflex:
pupil of the opposite eye constricts
BY Muhammad Ramzan Ul Rehman Nishtar Ken 23

24. BY Muhammad Ramzan Ul Rehman Nishtar Ken 24

25. miosis: decreasing of pupillary
aperture due to stimulation of
parasympathetic nerves that excite the
pupillary sphincter muscle
mydriasis: dilation of pupillary
aperture due to stimulation of
sympathetic nerves that excite the
radial fibers of the iris
BY Muhammad Ramzan Ul Rehman Nishtar Ken 25

26.  Pupil that fails to respond to light but does respond to accommodation and
is very small in size.
 It is an important diagnostic sign of CNS disease (syphilis).
BY Muhammad Ramzan Ul Rehman Nishtar Ken 26

27.  The sympathetic nerves to the eye are occasionally interrupted . Interruption
occurs in cervical sympathetic chain.
BY Muhammad Ramzan Ul Rehman Nishtar Ken 27

28.  One pupil remains persistently
constricted to a smaller diameter
than the pupil of the opposite eye
(miosis)
 Drooping of Upper eyelid (ptosis)
 Blood vessels on the corresponding
side of the face & head become
persistently dilated (flushing of
face)
 Sweating can’t occur on the
affected side of the face
(anhydrosis)
BY Muhammad Ramzan Ul Rehman Nishtar Ken 28

29. BY Muhammad Ramzan Ul Rehman Nishtar Ken 29

30. Lister’s perimeter
 Perimetry maps and quantifies the
visual field, especially at the
extreme periphery of the visual
field.
BY Muhammad Ramzan Ul Rehman Nishtar Ken 30

31. BY Muhammad Ramzan Ul Rehman Nishtar Ken 31

32. BY Muhammad Ramzan Ul Rehman Nishtar Ken 32

33. Physiologic blind spot: In all
perimetry charts, a blind spot
caused by lack of rods and cones in
the retina over the optic disc is
found about 15 degrees lateral to
the central point of vision, as
shown in the figure.
 Scotoma
A blind spot in any other portion of
the visual field
BY Muhammad Ramzan Ul Rehman Nishtar Ken 33

34.  nasal field located on the temporal side of the
retina
 temporal field located on the nasal side of the
retina
 interruption of the visual pathway at different
points leads to very specific visual field defects
 “blind spot” located about 15 degrees lateral to
the central point of vision
 no rods or cones in this area, called the optic
disc, exit point for axons of the ganglion cells
BY Muhammad Ramzan Ul Rehman Nishtar Ken 34

35. By Muhammad Ramzan Ul Rehman
BY Muhammad Ramzan Ul Rehman Nishtar Ken
35