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OCULAR ANATOMY > OPTIC NERVE VISUAL PATHWAYS > Flashcards

OPTIC NERVE VISUAL PATHWAYS Flashcards

1
Q

Which of the following visual pathway structures carries information from the optic chiasm to the lateral geniculate nucleus?

A

Optic tract

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2
Q

Which of the following parts of the optic nerve goes through the optic canal?

A

Intracanalicular

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3
Q

Which of the following orders best represents the neuroretinal rim from thickest to thinnest?

A

Inferior-superior-nasal-temporal

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4
Q

Which of the following tissues separates the optic nerve fibers from the choroid?

A

Tissue of Jacoby

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5
Q

When the ganglion cells axons exit the lamina cribosa they are myelinated by which of the following cells?

A

Oligodendroglial

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6
Q

When the ganglion cells axon bundles exit the lamina cribosa they are surrounded by which of the following cells?

A

Astrocytes

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7
Q

When the ganglion cells axon bundles exit the lamina cribosa they are separated by connective tissue derived from which of the following meningeal layers?

A

Pia

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8
Q

The radial peripapillary capillaries are located in which of the following retinal layers?

A

Nerve fiber layer

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9
Q

The prelaminar surface of the optic disc is supplied by which of the following blood sources?

A

Central retinal artery

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10
Q

Which of the following statements best describes the location of the internal carotid artery in relation to the optic chiasm?

A

Lateral to the optic chiasm

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11
Q

The majority of the left nasal ganglion cell axons terminate in which of the following locations?

A

Right lateral geniculate nucleus

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12
Q

The left temporal ganglion cell axons will terminate in which of the following locations?

A

Left lateral geniculate nucleus: layers 2, 3, 5

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13
Q

The optic radiations that form Meyer’s loop carry _____ retinal information and travel through the _____ lobe

A

inferior; temporal

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14
Q

Which of the following visual cortex areas receive information from the right superior temporal retina?

A

Right cuneus

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15
Q

The visual cortex is primarily supplied by which of the following arteries?

A

Posterior cerebral artery

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16
Q

What are laminar dots?

A

Pores seen at the base of the optic cup

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17
Q

Superior temporal retinal fibers damage leads to ____ visual field defects.
Inferior temporal retinal fibers damage leads to _____ visual field defects.

A

Inferior nasal; superior nasal

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18
Q

What are the 2 parts of the optic disc?

What do the 2 parts of the optic disc contain?

A
  1. Optic cup - central depression containing connective tissue through which the CRA & CRV pass to enter the retina
  2. Neuroretinal rim (NRR)
    – is pale pink (or orange) in color
    − mainly composed of ganglion cell
    axons along with glial supportive cells (astrocytes) and blood vessels
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19
Q

Ganglion cell axons from this part of the retina enter the superior part (i.e. 12 o’clock position) of the optic disc’s neuroretinal rim:

State where the visual field defect will be if this area of the neuroretinal rim of the optic disc is damaged by glaucoma

A

The course of the ganglion cell axons within the nerve fiber layer of the retina has a characteristic pattern:
− Axons from the nasal retina pass into the nasal part of the optic disc
− Axons from the superior temporal retina (ST) pass into the superior part of the optic disc.
− Axons from the inferior temporal retina (IT) pass into the inferior part of the optic disc
− Axons originating from the macular region (including the fovea) pass directly into the temporal part of the optic disc as the papillomacular bundle.

The visual field defect would be INFERIOR-NASAL

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20
Q

State the blood supply to each region. Be complete.

  • neuroretinal rim
  • prelaminar part of optic nerve
  • postlaminar part of optic nerve adjacent to eyeball
  • postlaminar part of optic nerve 5mm anterior to optic chiasm
A

Neuroretinal rim: pial plexus (?)

Prelaminar part of optic nerve: radial peripapillary capillary plexus (off retinal arterioles that branch off CRA)
-between NFL/lamina cribrosa: supplied by peripapillary choroid nerve (receiving blood from SPCA)

Postlaminar part of optic nerve adjacent to eyeball:
supplied both by SPCA directly & branches of the circle of Zinn-Haller (branches of SPCA)

Postlaminar part of optic nerve 5mm anterior to optic chiasm: more central portion is supplied by branches of the central retinal artery (CRA)

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21
Q

The thinnest part of the neuroretinal rim is the ______ region. (superior, inferior, nasal, temporal)

A

Temporal (ISNT rule from thickest to thinnest)

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22
Q

Before entering the optic tract, the ______ fibers cross in the posterior part of the optic chiasm.

A

Nasal

23
Q

Name the visual field defect seen in a patient who has compression of the inferior surface of the left optic tract. Be specific.

A

Right homonymous hemianopia

24
Q

Which layers of the left LGN do the left superior temporal retinal ganglion cell axons terminate in? Are they located in the central, medial, or lateral part of the LGN if:

  • they are from the superior retina?
  • they are from the inferior retina?

Which layers of the LGN receive input about spatial location and motion detection?

A

The left superior temporal retinal ganglion cell axons terminate in layers 2,3,5 (ipsilateral) on the medial part of the LGN. If the axons are from the superior retina, they terminate medially. If they are from the inferior retina, they terminate in the lateral LGN.

“M” cells

25
Q

The intraocular part of the optic nerve is located between ____ &______

A

The intraocular part of the optic nerve lies within the sclera. It extends from the internal limiting membrane (ILM) covering the optic disc to the posterior surface of the lamina cribosa.

26
Q

Which cells form the ILM over the surface of the optic disc?

A

The ILM at the optic disc is thinner and formed by processes of fibrous astrocytes and their basal lamina rather than Muller cell processes. This is because the retina is NOT present at the optic disc & therefore Muller cells are NOT present at the optic disc.

27
Q

What forms the stria of Gennari in primary visual cortex? Be specific.

Which layer of primary visual cortex does it lie in?

A

Visual cortex is identifiable on a histologic section by the presence of a white stripe in the cortex called the “stria of Gennari”

The myelinated axons of the LGN cells in layer 4b of the visual cortex, running parallel to the surface of the primary visual cortex, create a white line or stripe in layer 4b (“stria of Gennari”) that is not seen in other cortical areas of brain.

28
Q

State all the possible locations along the visual pathway where a lesion could cause the following visual defect. Include side of the body the lesion(s) would be on.
Locations:

If the lower right quadrant of the patient’s visual field is blacked out, in both eyes, what is the visual field defect?

A
  1. Optic nerve/retina of one eye
  2. Optic chiasm (nasal fibers compressed by pituitary tumor leading to temporal field loss in both eyes)
  3. Optic tract, LGN, or occipital lobe of one side
  4. Optic radiations in temporal lobe, or lingual gyrus of occipital lobe on one side
  5. Optic radiations in parietal lobe, or cuneus of occipital lobe on one side
  6. Lingual gyrus of occipital lobe

Right Inferior Quadrantonopia caused by left cuneus of occipital lobe being damaged or damage to optic radiations in left parietal lobe.

29
Q

Damage to the optic radiations in the temporal lobe leads to the following visual field defect. Draw the VF defect.

A

Superior Homonymous Quadrantonopia (pie in the sky)

30
Q

The longest part of the optic nerve is the _______ part.

A

The intraorbital portion of the optic nerve is the longest part, longer than the distance from eyeball to the optic canal- therefore giving it a slight S-shaped curve.

31
Q

Where the largest pores in the lamina cribosa? What is the clinical significance of that?

A

The largest pores are located superiorly and inferiorly in the lamina cribrosa, but these pores have a thinner connective tissue meshwork (than in nasal or temporal regions of the lamina cribrosa).

This suggests the superior & inferior pores have less structural support for the axons passing through these pores. This suggests that the superior and inferior parts of the lamina cribrosa are its weakest sections and are therefore less able to resist deformation due to increased intraocular pressure, leading to compression of the ganglion cell axons passing through these pores.

32
Q

The bundles of 1000 ganglion cell axons in the prelaminar part of the optic nerve are surrounded by the following cells:

A

As the ganglion cell axons enter the neuroretinal rim, fibrous astrocytes bundle the axons into fascicles containing 1000 axons. The astrocytes surround the ganglion cell axons like tubes and capillaries course within the astrocyte tubes.

33
Q

The bundles of 1000 myelinated ganglion cell axons in the intraorbital part of the optic nerve are surrounded by the following cells:

A

As the ganglion cell axons exit the lamina cribrosa, each axon is myelinated by oligodendroglial cells, so each bundle of ganglion cell axons now contains 1000 myelinated axons surrounded by astrocytes (though fewer than in the prelaminar and laminar parts).

− Myelination increases the diameter of the optic nerve from l.5 mm to 4mm.
− The bundles are separated from each other by connective derived from the pia mater.

34
Q

Why does the optic disc swell with papilledema? In other words:
What gets compressed and where?
What does the compressing?
What causes the disc swelling?

A

Papilledema = optic disc edema (swelling of optic disc) secondary to increased intracranial pressure

Optic disc gets compressed due to increased intracranial pressure

What does the compressing? A space occupying lesion such as a tumor, subarachnoid hemorrhage, subdural hematoma, hydrocephalus, meningitis

The primary cause of the disc swelling is stasis of axoplasmic flow in the ganglion cell axons at the level of the lamina cribrosa with subsequent intra-axonal edema in the area of the optic disc.

35
Q

Blood supply to the primary visual cortex is provided by:

A

Although the visual cortex is mainly supplied by the posterior cerebral artery (PCA) a branch of the middle cerebral artery supplements the circulation at the occipital pole.

Posteriorly, near the occipital pole, branches of the middle & posterior cerebral arteries may anastomose providing a dual blood supply to the macular fibers.

36
Q

The circle of Zinn-Haller supplies these parts of the visual pathway. Be specific.

A

Circle of Zinn-Haller is a ring of blood vessels within the sclera, formed by the anastomoses of branches of the short posterior ciliary arteries (SPCA)

It supplies the laminar part of the optic nerve.

*(structures passing thru annulus of Zinn)
Superior division of the oculomotor nerve (CNIII)
Nasociliary nerve (branch of ophthalmic nerve)
Inferior division of the oculomotor nerve (CNIII)
Abducens nerve (CNVI)
Optic nerve
Annular muscles are found near pharynx.
From pharynx annular nerve goes into separate parts of pharynx.

37
Q

The average/approximate diameter of the optic disc is ______ mm.

A

1.5mm (slightly larger vertically)

38
Q

What forms the papillomacular bundle?

Where do its axons enter the neuroretinal rim of the optic disc?

A

Axons originating from the macular region (including the fovea) pass directly into the temporal part of the optic disc as the papillomacular bundle. The axons of the papillomacular bundle occupy 1/3 of the optic disc even though the macula encompasses only one twentieth of the retinal area.

39
Q

(CO) 1. Name all the structures in the visual pathway in proper order, beginning with ganglion cells

A

▪ Retina - retinal ganglion cell axons carry visual information out of retina via optic nerve
▪ Optic Nerve - composed of ganglion cell axons
▪ Optic Chiasm - ganglion cell axons rearranged
− Axons from nasal retina cross in the optic chiasm − Axons from temporal retina do not cross
▪ Optic Tract - carries rearranged axons from optic chiasm to lateral geniculate nucleus
▪ Lateral Geniculate Nucleus (LGN) - visual portion of the thalamus
▪ Optic Radiations - formed by axons of LGN neurons; carry visual information from LGN to
visual cortex
▪ Visual Cortex (striate cortex) - lies in occipital lobe on banks of calcarine fissure

40
Q

(CO) 2. For the optic disc and nerve fiber layer:
▪ state the approximate diameter of the optic disc
▪ name and describe the two parts of the optic disc
▪ describe what the neuroretinal rim contains
▪ describe how the ganglion cell axons are distributed in the neuroretinal rim of the optic
disc (i.e. what location the macular fibers occupy in the optic disc vs. superior & inferior temporal retinal fibers, nasal fibers, etc.) and know the visual field defects caused if axons in the neuroretinal rim of the optic disc are damaged
▪ describe the horizontal raphe and papillomacular bundle and what they represent and/ or their composition
▪ describe what cells form the internal limiting membrane over the optic disc
▪ describe the variations in thickness of the neuroretinal rim (and NFL)

A

> The width of the neuroretinal rim depends on the number of ganglion cell axons entering at a given location. Since the fovea is located slightly inferior to the center of the optic disc, more axons enter the temporal side of the disc inferiorly than superiorly, making the neuroretinal rim slightly thicker inferiorly.

> The superior & inferior temporal retinal fibers are separated at their origin by a horizontal raphe which extends from the extreme temporal retinal periphery to the fovea. The superior and inferior retinal fibers do NOT cross the horizontal raphe.

> The thickness of the neuroretinal rim varies in the 4 retinal quadrants
▪ The mnemonic ISNT lists the thicknesses of the neuroretinal rim from thickest to thinnest: (inferior → superior → nasal → temporal)

> The radial peripapillary capillaries (RPC) of the retina are the most superficial of the capillary layers and lie in the region where the NFL is thickest.

41
Q

(CO) 3. Describe the components of the prelaminar, laminar and postlaminar parts of optic nerve.
▪ Know whether these parts belong to intraocular or intraorbital part of optic nerve ▪ Be sure to include blood supply, cell types supporting the ganglion cells in
each portion, relationships of dura, arachnoid and pia to the myelinated axons of the optic nerve and whether the axons are myelinated or unmyelinated

A

PRELAMINAR
Location: from the internal limiting membrane (ILM) to the anterior border of the lamina cribrosa
Part of Optic Disc: Intraocular
Blood supply: capillaries in the region are continuous (not fenestrated) with a continuous basal lamina and zonula occludens junctions at the apicolateral borders of their endothelial cells
Cell types: fibrous astroctyes (supportive) & blood vessels; surface of optic disc covered with ILM. Very little CT.
Relationship to dura/arachnoid/pia:
-optic nerve separated from retinal layers (intermediary tissue of Kuhnt)
-optic nerve separated from choroid (border tissue of Jacoby)
-the two glial sheaths are surrounded by a CT from sclera called border tissue of Elschnig
Myelination: unmyelinated ganglion cell axons

LAMINAR
Location: extends through the lamina cribrosa
Part of Optic Disc: Intraocular
Blood supply:
Cell types: bundles of ganglion cell axons continue to be directly surrounded by astrocytes, but the bundles are separated by the scleral collagen that forms the lamina cribrosa
Relationship to dura/arachnoid/pia:
Myelination:

POSTLAMINAR
Location: The intraorbital part of the optic nerve starts as the optic nerve leaves the lamina cribrosa
Part of Optic Disc: forms the post-laminar (retrolaminar) part of the optic nerve
Blood supply: pial septae will also transmit blood vessels & nerves into the substance of the intraorbital part of the optic nerve
Cell types:
Relationship to dura/arachnoid/pia: external surface of the optic nerve is ensheathed by the meninges (dura,
arachnoid, pia)
-bundles are separated from each other by connective derived from the pia mater
Myelination: axons of the ganglion cells are myelinated by oligodendroglial cells

42
Q

(CO) 4. Describe the 4 parts of the optic nerve in detail. Be sure to include:
▪ the locations of the 4 parts of optic nerve including where they begin and end
▪ which part is the longest and shortest
▪ where the optic nerve becomes myelinated and what cells myelinate the axons
▪ blood supply of the intraocular and intraorbital parts and what blood vessels they originate from.
(For example, what is the origin of the radial peripapillary capillary plexus? etc.)
▪ Relationships of 3 meningeal layers to optic nerve and what they fuse with anteriorly and posteriorly.
▪ Clinical significance of the subarachnoid space by optic nerve. Be able to explain what happens anatomically to cause papilledema.
▪ where the CRA pierces the optic nerve

A

INTRAOCULAR
-part that is clinically visible; divided into optic cup and neuroretinal rim (NRR)-ganglion cell axons
-central depression of optic cup contains CT where CRA/CRV passes
-optic disc has only NFL + ILM (blind spot)
-NFL contains unmyelinated GCs converging on optic disc; at the optic disc, they make a 90 degree turn and enter the NRR (see previous question for course GC axons take in NFL)
-thickest to thinnest: follow ISNT rule
-contains prelaminar (unmyelinated GC axons + fibrous astrocytes + blood vessels) and laminar parts (myelinated AFTER this part)
Blood: surface of optic disc (radial peripapillary capillary plexus- off arterioles of CRA), remaining prelaminar behind NFL/lamina cribrosa (peripapillary choroid off SPCA), laminar (SPCA + branches of circle of Zinn)

INTRAORBITAL
*longest part (S-shape)
Path: starts as optic nerve leaves lamina cribrosa; forms post-laminar part
-myelination occurs by oligodendrial cells; external surface ensheathed by meninges (makes optic n. part of CNS)
-each bundle of GCs is now 1000 myelinated axons surrounded by astrocytes
-at the optic canal, periosteum of dura fuses w/ periorbita of orbit at subarachnoid space
Blood: (central) CRA and CRV pierce dural sheath behind eyeball; (peripheral) pial plexus (from ophthalmic, CRA, circle of Zinn)

INTRACANALICULAR
Path: in lesser wing of sphenoid, surrounded by meninges + subarachnoid space
Blood: shares optic canal with inferiolateral ophthalmic artery
Blood: pial plexus (from ophthalmic artery)

INTRACRANIAL
Path: optic nerve exits the optic canal and it ends when the optic nerve reaches the optic chiasm
* The diaphragma sella (dura overlying the pituitary gland) and anterior part of the cavernous sinus lie below it
Blood: pial plexus (from ophthalmic artery)

*increased intracranial pressure leading to papilledema most likely to be caused by occupation or lesioning of the subarachnoid space (largest space behind eyeball)

43
Q

(CO) 5. Describe the structural anatomy of the lamina cribrosa. Be sure to include:
▪ which layer of the eyeball it’s continuous with
▪ presence of lamellae and cell types and fiber types in it
▪ pores (including variations in pore size, what passes through central pores,
what passes through it, location of largest pores and what fibers pass through
the largest pores and its clinical significance).

A

> The lamina cribosa is a continuation of the sclera across the posterior scleral foramen.

> It is composed of 3-10 dense connective tissue sheets (lamellae) which blend with and are anchored to the sclera at the periphery. Each lamella has an elastic fiber core surrounded by collagen & a basal lamina belonging to fibrous astrocytes.

> The lamellae of the lamina cribrosa are separated from each other by fibrous astrocytes

> The lamellae are fenestrated to allow the bundles of ganglion cell axons to pass through

> The pores are generally aligned in successive lamellae to allow the bundles of ganglion cells to easily pass through the pores (fenestrations)

> The largest pores are located superiorly and inferiorly in the lamina cribrosa, but these pores have a thinner connective tissue meshwork

44
Q

(CO) 6. Describe the optic chiasm. Include:
▪ which parts of the visual pathway it connects
▪ know which nasal fibers cross in anterior part of the optic chiasm vs. posterior part.
▪ Understand the type of visual field defects that can occur if the optic chiasm is damaged or compressed nasally vs. temporally

A

Important anatomical relationships:
− Anterior: the anterior cerebral arteries & anterior communicating artery
− Lateral: the internal carotid artery
− Inferior: diaphragma sella & pituitary gland

> The nasal fibers from each retina cross at the optic chiasm and enter the optic tract on the opposite side
− Inferior nasal retinal fibers cross in the anterior part of the optic chiasm
− Superior nasal retinal fibers cross in the posterior part of the optic chiasm

45
Q

(CO) 7. Describe the optic tract. Include:
▪ which parts of the visual pathway it interconnects
▪ which neuron axons are in it
▪ where the fibers terminate
▪ what the brachium of the superior colliculus contains and which parts of the visual pathway it interconnects
− what function the pretectal nuclei are involved in
▪ understand the type of visual field defect that occurs if the tract is damaged (superiorly,
inferiorly, completely).

A

> Connects optic chiasm and LGN (“The optic tract is a band of fibers that leave the posterior part of the optic chiasm. Most optic tract fibers terminate in the LGN of the thalamus.
Some send collateral branches to pretectal nuclei while going to the LGN. Around 1% leave the optic tract to the brachium of the superior colliculus to either terminate in the pretectal nuclei or superior colliculus

46
Q

(CO) 8. Describe the lateral geniculate nucleus in detail. Be sure to include what parts of the visual
pathway it interconnects. Describe its 6 layers including:
▪ Which fibers terminate in the 6 layers (be specific such as ipsilateral or contralateral retinal info)
▪ which are the parvocellular layers and which the magnocellular layers and what the
cells in the P and M layers are sensitive to.
▪ Know where the macula, inferior and superior retinal information is located in the LGN.
▪ Understand & describe the types of visual field defects that can occur if the LGN is
damaged (all of it on 1 side, just medial 1⁄2 or just lateral 1⁄2)

A

> The LGN is the visual relay center of the thalamus (swelling on posterior-inferior thalamus which sends info to visual cortex)

> Dorsal LGN has 6 layers (1, 4, 6 receive contralateral retinal input; 2, 3, 5 receive ipsilateral).

> Layers 1 + 2 are magnocellular (spatial localization/motion) and Layers 3-6 are parvocellular

> Lateral LGN receives input from inferior retina
Medial part receives input from superior retina
Macular fibers take up large central portion of LGN
(see PUTTING IT ALL TOGETHER pic)

47
Q

(CO) 9. Describe the optic radiations in detail. Include:
▪ which parts of the visual pathway it interconnects
▪ the fibers it contains
▪ Describe the paths of the optic radiations through the parietal and temporal lobes in
detail and where they terminate and what parts of the retina they represent.
▪ Understand & describe the types of visual field defects that can occur if the optic
radiations are damaged anywhere along their length. ▪ Understand what the loop of Meyer is

A

> Part of the geniculocalcarine pathway connecting LGN to visual cortex

> It is formed by axons from the LGN

> Axons from lateral LGN carry inferior retinal information through temporal lobe to visual cortex. All the fibers pass posteriorly to terminate in primary visual cortex of the lingual gyrus of the occipital lobe.
*Meyer’s loop= made of the few optic radiation fibers looping around lateral ventricle in temporal lobe

> Axons from medial LGN carry superior retinal information through parietal lobe, terminating in the primary visual cortex located in the cuneus of the occipital lobe.

48
Q

(CO) 10. Describe the primary visual cortex in detail. Include:
▪ its location in occipital lobe (relate to calcarine fissure as well as lingual gyrus and cuneus)
▪ where in the primary visual cortex the different parts of the retina (macula, peripheral retina, superior retina, inferior retina) are represented
▪ describe visual field defects if cuneus or lingual gyrus or whole occipital lobe are damaged by a tumor or stroke
▪ describe its blood supply.
▪ Explain what the line (stria) of Gennari is formed by and which layer of the primary visual cortex it lies in
▪ Understand and be able to explain why the macular region of primary visual cortex can be spared despite the reminder of the primary visual cortex being damaged
▪ Know in which layer of the visual cortex the LGN cells terminate

A

> Occupies the banks of the calcarine fissure on the medial surface of the occipital lobe in the cuneus & lingual gyrus

> Visual Representation
Macula = represented in the posterior part of
primary visual cortex near the occipital pole (about a third of the visual cortex)
Peripheral retina = represented in the anterior portion of the primary visual cortex
Superior retina = terminates in visual cortex above calcarine fissure, in the cuneus
Inferior retina = terminates in visual cortex below calcarine fissure in the lingual gyrus

> Visual field defect (all contralateral)
Cuneus: inferior homonymous quadrantonopia
Lingual gyrus: superior homonymous quadrantonopia
Occipital lobe: homonymous hemianopia

> Blood supply: Although the visual cortex is mainly supplied by the posterior cerebral artery (PCA) a branch of the middle cerebral artery supplements the circulation at the occipital pole.

> Stria of Gennari: myelinated axons of the LGN cells in layer 4b, running parallel to the surface of the primary visual cortex, create a white line or stripe in layer 4b

> Macular sparring: branches of the middle & posterior cerebral arteries may anastomose providing a dual blood supply to the macular fibers. So in patients with a right occipital lobe stroke from a right posterior cerebral artery occlusion, the contribution from the right middle cerebral artery may prevent infarction of the occipital pole, where the macular fibers lie, thus preserving macular function.

> Layer of Visual cortex the LGN terminates: gray matter (layer 4b visual cortex)

49
Q

(CO) 11. Describe and be able to name the visual defect obtained if there is damage to structures along any part of visual pathway as discussed in class.

A

See pg. 43 and Visual Field Activity Key

50
Q

(CO) 12. Understand the terminology: homonymous, quadrantanopia, hemianopia, contralateral, ipsilateral

A

HOMONYMOUS (visual field loss occurs on the same side in both eyes)

QUADRANTANOPIA (right or left superior or inferior quadrant of the visual field is missing)

HEMIANOPIA (half of the visual field is missing)

CONTRALATERAL (opposite side)

IPSILATERAL (same side)

51
Q

(CO) 13. State the following facts about laminar dots:
▪ Which anatomical structure(s) laminar dots represent
▪ If laminar dots are seen, then what does that indicate clinically? (i.e. does the patient have
glaucoma? Is the optic cup deep? Both or what?)

A

Laminar dots are visible representations of the pores of the lamina cribrosa that the ganglion cell axons pass though. The pores are darker than the surrounding sclera tissue so the pores are easy to see.

The presence of laminar dots indicates that the optic cup is deep; their presence does not necessarily mean that the person has glaucoma; they might have glaucoma or they may just have a deep cup!

52
Q

(CO) 14. State the following facts about malinserted discs:
▪ What is anatomically occurring if someone’s optic disc is described as a “malinserted” disc?
▪ How is it different from the normal “insertion of the optic disc into the eyeball?
▪ What is the characteristic appearance of the optic disc as seen clinically with direct ophthalmoscopy that helps one recognize it as a malinserted disc?

A

> The optic nerve enters the eyeball obliquely

> The nasal aspect of the optic disc would appear elevated and its temporal half depressed. In normal circumstances, the optic disc margin is in the same plane as the retinal tissue adjacent to it (flat and distinct)

> This complicates the determination of C/D ratio of the optic disc. Crescents are often seen, temporally, in this case (benign isolated anatomical alterations)

53
Q

(CO) 15. State the following facts about “crescents” adjacent to the optic disc:
▪ Which parts of the eyeball are missing (absent) at a scleral crescent?
▪ Which parts of the eyeball are present at a scleral crescent?
▪ Which parts of the eyeball are missing (absent) at a choroidal crescent?
▪ Which parts of the eyeball are present at a choroidal crescent?
▪ The usual location of crescents relative to the disc (i.e. superior, inferior, nasal or temporal to the disc?)

A
  • Scleral crescents are often associated with high myopia due to elongation of the eyeball.

SCLERAL CRESCENT
-white region along the temporal edge of the optic disc; directly viewing sclera
Missing: choroid, RPE
Present: 9 sensory layers of the retina (stretched/thinned)

CHOROIDAL CRESCENT
-dark band along the temporal edge of the optic disc; directly viewing choroid
Missing: RPE
Present: 9 sensory layers of the retina (stretched/thinned)

OCULAR ANATOMY (16 decks)

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