Retina to Brain Visual Pathway

Question 1

The visual pathway is the: optic nerve, optic chiasm, optic tract, and optic radiation (geniculocalcarine tract)

What are each parts of the pathway composed of?

Answer 1

The optic nerve, optic chiasm and and optic tract are all composed of retinal ganglion cell axons.

The otptic radiation is composed of LGN cell axons. This carries the signal from the LGN to the primary visual cortex.

Question 2

Why is the ON not a “True” peripheral nerve?

Answer 2

1. It is an extension of the brain tract
2. It is myelinated by oligodendrocytes (CNS) and not schwann cells (PNS)
3. Most of it is covered by the 3 layers of the meninges, including the subarachnoid with surrounding CSF

Question 3

Location of retinal nerve fibers comprising the optic nerve from the optic disc to orbit

Answer 3

Macular fibers make up the largest wedge temporally.
Superior temporal fibers- superior wedge
Inferior temporal fibers- Inferior wedge
Superior nasal fibers- SN wedge
Inferior nasal fibers- IN wedge

Question 4

Location of ganglion cell axons comprising the optic nerve from the orbit to the cranium (anterior to pituitary gland)

Answer 4

Macular fibers- Central 
Superior temporal fibers- ST quad 
Inferior temporal fibers- IT quad
Superior nasal fibers- SN quad
Inferior nasal fibers- IN quad

Question 5

Along its path, the ON is divided into which 4 sections?

Answer 5

Intraocular (1 mm)
Intraorbital (25-30mm)
Intracanalicular (6-10mm) In the optic canal
Intracranial (10-16mm)

Question 6

Intraocularlly, the nerve fibers (The ON) are separated from retinal layers by ___

Answer 6

A ring of glial tissues called the intermediary tissue of kuhnt.

Question 7

Continuation of the intermediary tissue of Kuhnt (Same glial tissue)

Answer 7

The border tissue of Jacoby continues posteriorly. This separates the nerve fibers from the choroid.

Question 8

Border tissue of Elschnig

Answer 8

A ring of collagenous tissue derived from sclera.
Lies outer to glial tissue (Intermediary of kuhnt and border tissue of jacoby)
Has two regions: Prelaminar and Laminar

Question 9

Glial tissue that surrounds ON

Answer 9

Intraocularly. The intermediary tissue of Kuhnt separates the retina from the ON.

The Border Tissue of Jacoby separates the choroid from the ON.

Same glial tissue. A continuation.

Question 10

The two divisions of the border tissue of Elschnig that is intraocularly

Answer 10

Prelaminar is intraocular. Extends from the optic disc to the lamina cribrosa. Not myelinated. Sheathes of astrocytes bundle the nerve fibers into ~1,000 fascicles.

Laminar region is intraocular. Includes fibers that extend through the lamina cribrosa. At the posterior portion of the lamina cribrosa, the fibers become myelinated.

(lamina cribrosa may be a barrier to oligodendrocytes)

Question 11

The infraorbital portion of the ON extends from __ to ___

Answer 11

The posterior margins of the sclera to the optic canal. Courses medially to reach the optic canal.

Question 12

Why does the length of the ON within the infraorbital part exceed the distance from the globe to the optic canal?

Answer 12

Slight sine wave shaped curve. Allows for full eye movement without stretching of the nerve.

Question 13

The infraorbital region of the ON is covered by 3 layers of

Answer 13

Meninges that fuse and merge with the sclera.

Pia- innermost. Loose, vascularized connective tissue. Separates fiber bundles until the optic chiasm (takes over for the astrocytes)

Arachanoid- Web of collagen with CSF in the subarachnoid space. Surrounds ON, but stops once it reaches posterior sclera on the back of the eye.

Dura- Tough, dense connective tissue with elastic fibers.

Question 14

Pia septa in the intraorbital space has a similar role to which cell from the intraocular space?

Answer 14

Astrocytes in the intraocular space (mostly the prelaminar division) bundle the nerve fibers into fascicles.

The pia in the infraorbital space separate the fiber bundles.

Question 15

Difference between the intermediary tissue of Kuhnt and the border tissue of Jacoby

Answer 15

Intermediary tissue of Kuhnt- Separates ON from retina

Border tissue of Jacoby- Separates ON from choroid.

Question 16

Intracanalicular division of the ON

Answer 16

Is the portion of the ON within the optic canal. Accompanied by the ophthalmic artery.

Question 17

mm in length of each division of the ON

Answer 17

Intraocular- 1mm (shortest)
Intraorbital- 25-30mm (longest)
Intracanalicular- 6-10mm
Intracranial- 10-16mm

Question 18

The optic chiasm is usually located where and lies within what

Answer 18

Located anterior to the pituitary gland. in 10% of people, it is displaced more anterior, and in 15% of people, it is displaced posteriorly.

Lies within the circle of willis.

Question 19

At the optic chiasm, what do nasal fibers do?

Answer 19

SOME Inferior nasal fibers loop contralaterally to form the anterior knee of wildebrand and then continue down the contralateral side.

SOME Superior nasal fibers loop ipsilateral to form the posterior knee of hildebrand and then continue down the contralateral side.

Others will make a direct and efficient cross.

Question 20

Big picture. The optic tract is divided into

Answer 20

The small medial root (10% of fibers head here)

The large lateral root (90% of fibers head here)

Question 21

The small medial root, which is where 10% of ON fibers travel along the optic tract, has 4 terminations where

Answer 21

1. Several - Superior colliculus, eye/head movements
2. People - Pretectal nuclei, pupillary light reflex
3. Purchased - Paracellular reticular formation, arousal
4. Houses - Hypothalamus, circadian rhythm

Question 22

The large medial root, which contains 90% of the optic tract fibers, synapses where?

Answer 22

With neurons in the LGN of the thalamus.

Question 23

Optic radiation. Where do superior fibers and inferior fibers travel and terminate?

Answer 23

Superior fibers travel through the parietal lobe and then terminate at the cuneus gyrus, which is above the calcarine sulcus.

Inferior fibers travel anteriorly into the temporal lobe at first, which is called meyer’s loop, and then travels posteriorly to terminate at the lingual gyrus, which is below the calcarine sulcus.

Macular fibers are generally situated between superior and inferior fibers.

Question 24

Primary visual cortex can also be called

Answer 24

Striate cortex, Area 17, Brodmann 17, V1

Question 25

The primary visual cortex is located where

Answer 25

Located at the most posterior aspect of the occipital lobe. It extends into the medial surface of each hemisphere, where it is largely buried within the calcarine fissure.

Question 26

Fibers representing central retina terminate where at the primary visual cortex?

Answer 26

At the most posterior aspect. Accounts for 1/3 of the visual cortex.

Question 27

Fibers representing peripheral retina terminate where at the primary visual cortex?

Answer 27

Terminate at the anterior aspect of the cortex, medial in the calcarine fissure.