Neurology | Optic Nerve | Cranial Nerve II: Visual Pathway and Lesions

Summary

This educational video script delves into the intricacies of the human visual pathway, starting from the retina's interaction with light to the processing in the brain. It explains the journey of visual information through the optic nerve, optic chiasma, and lateral geniculate nucleus, highlighting how lesions at various stages can lead to different visual field defects. The script aims to clarify complex concepts like nasal and temporal hemiretina, homonymous hemianopia, and the impact of damage to the optic radiations and occipital cortex, using visual aids to illustrate the effects on visual fields.

Takeaways

• 👁 The video discusses the visual pathway, detailing how light hits the retina and is processed through the optic nerve and other components.
• 🌟 It emphasizes the importance of understanding the phototransduction cascade for those who have seen the related video, as it explains the conversion of light into chemical and electrical changes.
• 🔍 The script explains the concept of visual fields, distinguishing between the nasal and temporal components and how they relate to the right and left visual fields of each eye.
• 🤔 It clarifies potential confusion by redefining the terms for the visual fields, ensuring that the audience understands which part of the brain processes which visual field.
• 💡 The video describes how the retina's temporal hemiretina receives light from the opposite visual field, and how this information is transmitted to the brain without crossing over.
• 🔄 At the optic chiasm, fibers from the nasal hemiretina cross over to the opposite side of the brain, while fibers from the temporal hemiretina stay on the same side.
• 🧠 The optic tract carries visual information to the lateral geniculate nucleus (LGN) in the thalamus, which is a crucial part of the visual pathway.
• 📏 The LGN is structured in six layers, with ipsilateral fibers connecting to layers two, three, and five, and contralateral fibers to layers one, four, and six.
• 🌐 Some fibers from the LGN project to the midbrain, affecting the pupillary light reflex and involving structures like the superior colliculus and pretectal nucleus.
• 🧬 The majority of fibers from the LGN continue to the occipital lobe, specifically to the striate cortex, which is the primary visual cortex responsible for visual perception.
• 🛑 The script also covers the implications of various lesions in different parts of the visual pathway, explaining the resulting visual field deficits such as monocular blindness, homonymous hemianopia, and quadrantanopia.

Q & A

What is the primary focus of the video script?

The video script primarily focuses on explaining the visual pathway, detailing how light hits the retina and is processed through the optic nerve and other components of the visual system.

What is the significance of the phototransduction cascade in the visual pathway?

The phototransduction cascade is significant because it is the process by which light is converted into chemical and then electrical changes, which are essential for the visual pathway to function properly.

How does the script define the visual field and its components?

The script defines the visual field as the area that can be seen at any given moment. It is divided into components such as the nasal and temporal components, which are related to the proximity to the nose and temple, respectively.

What is the role of the optic nerve in the visual pathway?

The optic nerve plays a crucial role in the visual pathway by transmitting the visual information from the retina to the brain. It is composed of the ganglion cell axons that carry the information after phototransduction.

Can you explain the concept of the optic chiasma in the visual pathway?

The optic chiasma is a structure where the optic nerves from both eyes meet. Here, the fibers from the temporal hemiretina cross over to the opposite side, while the fibers from the nasal hemiretina remain on the same side, allowing for the integration of visual information from both eyes.

What is the optic tract and where does it lead?

The optic tract is a long tube-like structure that extends from the optic chiasma. It carries the visual information from the retina to the lateral geniculate nucleus in the thalamus.

How does the script describe the organization of the lateral geniculate nucleus (LGN)?

The script describes the LGN as having six layers, with ipsilateral fibers (from the temporal hemiretina) going to layers two, three, and five, and contralateral fibers (from the nasal hemiretina) going to layers one, four, and six.

What are the two types of fibers mentioned in the script that contribute to the visual pathway, and how do they differ?

The two types of fibers mentioned are the ipsilateral fibers and the contralateral fibers. Ipsilateral fibers stay on the same side of the brain and come from the temporal hemiretina, while contralateral fibers cross to the opposite side of the brain and come from the nasal hemiretina.

What is the striate cortex and its relevance to the visual pathway?

The striate cortex, located in the occipital lobe, is the primary visual cortex. It is the area where the perception of visual stimuli occurs, processing the information received from the optic radiations.

How does the script explain the impact of different types of lesions on the visual pathway?

The script explains that lesions in different parts of the visual pathway can result in various types of visual field loss, such as monocular blindness, homonymous hemianopia, and quadrantanopia. The specific type of visual impairment depends on the location and extent of the lesion.

Outlines

00:00

👀 Introduction to the Visual Pathway

The script begins by introducing the visual pathway, focusing on how light hits the retina and travels through the optic nerve. It emphasizes the importance of understanding the phototransduction cascade, which converts light into chemical and electrical changes. The video explains the concept of visual fields, distinguishing between the nasal and temporal components for both the right and left eyes. It clarifies potential confusion by redefining the terms for the visual fields as they relate to the right and left eyes, ensuring the viewer grasps the basics before delving into more complex topics.

05:00

🔄 Optic Nerve Crossing and Pathways

This paragraph delves into the mechanics of the optic nerves, explaining how the fibers from the temporal hemiretina cross over at the optic chiasm, while those from the nasal hemiretina do not. It describes the optic tracts and how the fibers from each eye are directed to the opposite side of the brain. The script uses the mnemonic 'anything from the right goes to the left, and anything from the left goes to the right' to help viewers remember the pathway of the visual information. It also introduces the concept of ipsilateral and contralateral fibers, which are crucial for understanding the effects of various lesions on vision.

10:01

🌐 Lateral Geniculate Nucleus and Visual Processing

The script moves on to the lateral geniculate nucleus (LGN) within the thalamus, highlighting its six layers and explaining the distribution of ipsilateral and contralateral fibers to different layers. It discusses the importance of the LGN in processing visual information before it is sent to other parts of the brain. The paragraph also touches on the connections between the LGN and the midbrain, specifically mentioning the superior colliculus and the pretectal nucleus, which are involved in the pupillary light reflex and other visual responses.

15:02

🧠 Optic Radiations and the Visual Cortex

The discussion continues with the optic radiations, which are the fibers that carry visual information from the LGN to the occipital lobe. The script differentiates between the superior and inferior retinal fibers, also known as the Bärum's loop and Meyer's loop, respectively. It explains how these fibers reach the striate cortex, also known as the primary visual cortex, where the perception of visual stimuli occurs. The paragraph also introduces the concept of lesions and how they can affect the visual field, providing a foundation for understanding the clinical implications of damage to different parts of the visual pathway.

20:03

🛑 Lesions and Their Impact on Vision

This paragraph explores various hypothetical lesions that could affect the visual pathway, from damage to the optic nerve causing monocular blindness to lesions in the optic chiasm leading to bitemporal hemianopia. The script describes the visual field deficits associated with each type of lesion, such as right homonymous hemianopia resulting from damage to the optic tract. It uses visual aids to illustrate the effects of these lesions on the visual fields, helping viewers to understand the clinical manifestations of different types of damage to the visual pathway.

25:07

🔍 Superior and Inferior Retinal Fibers Lesions

The script focuses on the impact of lesions affecting the superior and inferior retinal fibers, also known as Bärum's loop and Meyer's loop. It explains how damage to these fibers can lead to specific types of visual field loss, such as left inferior quadrant hemianopia or right superior quadrant hemianopia. The paragraph uses detailed visual representations to show how the superior and inferior visual fields are affected by lesions in different parts of the visual pathway, providing a clear understanding of the consequences of such damage.

30:08

🌀 Optic Radiations Damage and its Effects

This paragraph discusses the effects of damage to the optic radiations, which can result in a loss of vision in both the superior and inferior planes of the visual field. The script describes the concept of homonymous hemianopia, which occurs when there is damage to the optic radiations on one side, leading to a loss of the same visual field in both eyes. It also explains how damage to the right optic radiations can result in left homonymous hemianopia, affecting the viewer's understanding of the comprehensive impact of such lesions.

35:10

🏥 Clinical Implications of Occipital Lobe Damage

The final paragraph addresses the clinical implications of damage to the occipital lobe, particularly the macular region, which is responsible for acute vision. The script explains how occlusion of the posterior cerebral artery can affect blood flow to the occipital lobe but spares the macula due to the blood supply from the middle cerebral artery. This can result in a unique condition where the peripheral vision is lost, but the central vision remains intact, a phenomenon referred to as hemianopia with macular sparing. The paragraph concludes by summarizing the key points discussed in the video and encourages viewers to engage with the content.

Keywords

💡Visual Pathway

The visual pathway refers to the route that visual information takes from the retina to the brain. In the video, the visual pathway is the central theme, explaining how light hits the retina and is processed through various structures until it reaches the brain. The script describes the pathway in detail, from the optic nerve to the optic chiasma and beyond.

💡Retina

The retina is the light-sensitive tissue at the back of the eye where the phototransduction process occurs. It is crucial for the initial stages of vision as it converts light into neural signals. The script mentions the retina in the context of how light hits it and initiates the visual process.

💡Phototransduction Cascade

Phototransduction cascade is the series of biochemical reactions that occur after light is absorbed by photoreceptor cells in the retina. The script emphasizes the importance of understanding this process before delving into the visual pathway, as it explains how light is converted into electrical signals.

💡Optic Nerve

The optic nerve is the bundle of nerve fibers that transmits visual information from the retina to the brain. In the script, the optic nerve is discussed as part of the visual pathway, highlighting its role in carrying signals from the retina to the optic chiasma.

💡Optic Chiasma

The optic chiasma is the point where the optic nerves from both eyes meet and some of the nerve fibers cross from one side of the body to the other. The script explains the chiasma's role in the decussation of fibers, which is essential for understanding the distribution of the visual fields to the brain.

💡Visual Field

The visual field is the entire area that can be seen at one time without moving the eye. The script discusses the concept of the visual field in relation to the nasal and temporal components, explaining how different parts of the visual field correspond to different areas of the retina.

💡Nasal and Temporal Hemi-retina

The nasal and temporal hemi-retina refer to the parts of the retina that are associated with the nasal (closer to the nose) and temporal (closer to the temple) regions of the visual field. The script uses these terms to explain how the visual field is represented on the retina and how the information from each hemi-retina is processed differently in the brain.

💡Lateral Geniculate Nucleus

The lateral geniculate nucleus (LGN) is a part of the thalamus that receives and processes visual information before it is sent to the visual cortex. The script describes the LGN as a crucial relay station in the visual pathway, detailing its six layers and how different fibers from the eyes terminate in specific layers.

💡Optic Tract

The optic tract is the pathway that carries visual information from the optic chiasma to various parts of the brain. In the script, the optic tract is mentioned as the route that the visual signals take after leaving the optic chiasma, leading to the LGN and other brain areas.

💡Hemianopia

Hemianopia is a condition characterized by the loss of half of the visual field in both eyes. The script discusses different types of hemianopia that can result from lesions in various parts of the visual pathway, such as bitemporal hemianopia and homonymous hemianopia.

💡Striate Cortex

The striate cortex, also known as the primary visual cortex, is the area of the occipital lobe where the visual information is processed and perceived. The script mentions the striate cortex as the final destination of the visual pathway, where the perception of visual stimuli occurs.

Highlights

Introduction to the visual pathway, explaining how light hits the retina and its journey through the optic nerve and other processes.

Importance of understanding the phototransduction cascade for the visual pathway discussion.

Description of the right and left visual fields, and the nasal and temporal components of these fields.

Clarification of the confusion between the right eye's left visual field and the right visual field.

Explanation of how the temporal hemiretina receives light rays from the opposite visual field.

Crossing of fibers at the optic chiasm, where fibers from the right eye's nasal hemiretina cross to the left side.

Identification of ipsilateral and contralateral fibers and their respective paths in the visual pathway.

Role of the optic tract in transmitting visual information from the optic chiasm to the brain.

Function of the lateral geniculate nucleus in the thalamus and its six layers' involvement in processing visual information.

Distribution of ipsilateral and contralateral fibers to specific layers in the lateral geniculate nucleus.

Connection of fibers to the midbrain, specifically the superior colliculus and pretectal nucleus, for reflex actions.

Path of fibers through the temporal and parietal lobes to the occipital lobe, highlighting the difference between superior and inferior retinal fibers.

Importance of the striate cortex in the occipital lobe as the primary visual cortex for visual perception.

Clinical implications of lesions in different parts of the visual pathway and their effects on visual fields.

Description of specific types of visual field loss due to lesions in the optic nerve, optic chiasm, and optic tract.

Impact of damage to the optic radiations and its similarity to homonymous hemianopia.

Special case of occipital lobe damage sparing the macula, resulting in hemianopia with macular sparing.

Conclusion summarizing the visual pathway processing, associated lesions, and their clinical relevance.

Transcripts

I'm in Aries in this video we're going

to talk about specifically the visual

pathway so we're going to take how the

light hits the retina and we're going to

take it through the optic nerve and all

the other different process if you guys

have already watched our video on the

phototransduction cascade that's going

to be very very important that you do

that before we get into this visual

pathway because we already talked about

exactly how those light rates got

converted into chemical changes and then

electrical changes and how they went

down the axon to the ganglion cells

which basically made up the optic nerve

all right so now we're going to have two

eyeballs right this is the we're going

to say this the left eyeball and this is

the right eyeball okay now first things

first

what I want us to try to imagine if

we're gonna put a lot of different

concepts together when you guys are

looking you guys are like looking at

anything around you we our eyes are so

amazing that they can pick up different

types of visual fields so for example

this is the right visual field or the

right visual field and this is the left

eyes visual field

okay so what is this one right here this

is the right eyes visual field and this

one over here is the left eyes visual

field okay now with in the visual field

you have two different components of

this visual field we're going to say

this is the nasal so since your you'd

have your honker right there pretend

this is your nose okay so pretend this

structure here is your nose okay since

this is the nose these two structures

that are near the nasal region this is

the nasal component of the visual field

alright so this is the nasal component

of the visual field and then this one

over here would be near the temple so

this is the temporal component of the

visual field and this over here is going

to be the

temporal component of the visual field

okay now to make it easy though now that

we know that this is what it is it's

nasal and the temporals these words are

going to get interchanged a lot so I do

not want to confuse you guys so what I'm

going to do is for the sake of it is I'm

going to switch nasal and since this is

the right visual field this is what gets

confusing the right visual field has a

left visual field and a right visual

field okay so the right eye has a left

visual field and a right visual field so

we're going to say this is the left

visual field and this is the right

visual field okay so I just want to make

it as simple as I possibly can here this

whole right eye is going to have two

fields it's going to have the right

visual field and last visual field same

thing this left eye is going to have two

visual fields it's going to have a left

visual field and a right visual field

okay simple as that now we're going to

be able to kind of do this a lot easier

now so instead of using the words nasal

and tempore but understand those words

because it's going to be important

lesions okay let's say first off when

we're looking out let's say that this

part of the retina there's two parts of

the retina so this is the right eye this

part of the retina is closest to the

temple or the right temple right so

we're going to call this part of the

retina we're going to call this the

temporal Hemi retina okay that's a

temporal Hemi retina now here's what

gets really funky the temporal Hemi

retina is receiving light rays from the

left visual field okay so from here this

part here this left visual field is

hitting this part of the retina okay so

if light rays from the left visual field

are hitting this part of the hit retina

that temporal heavy right now

but then the what is this one this one

is close to the actual nose so since

it's close to the nose this is called

the nasal right Hemi retina so it's

called the nasal hemorrhage now and it's

called the temporal Hemi retina the

nasal hemorrhage now is receiving light

from the right visual field so the nasal

Henry retina is getting hit with light

from the right visual field all right so

just to make sure we're clear left

visual field hits the temporal hit me

right now and the right visual field

hits the nasal heavy retina sweet deal

same thing would happen up here what

would this one be this one right here

would be the temporal Hemi retina want

to put a char here and this right up

here is going to be the nasal Hemi

retina okay and same thing nasal heavy

rain is going to be receiving visual

field from left visual field so it's

going to be getting it from the left

visual field and then the temporal Hemi

retina on the left eyeball is going to

be receiving it from the right visual

field okay now that we're done with that

what happens with these fibers here's

what I want you to remember anything

from the right goes to the left anything

with the left goes to the right that's

it anything that's coming from the left

okay well this temporal Hemi retina this

is on the right eyeball okay so this is

the right eyeball it's picking up

information from the left visual field

well anything from the left has to go to

the right oh so these should stay on the

same side then so these fibers right

here they should not go and cross over

to the other side they should stay on

this same side so they're going to come

down the optic nerve and you know what

happens the two optic nerves actually

come together they come together and

form this big old structure that you

kind of see right here I'm actually not

going to do it in brown here because I'm

going to use this brown a lot

I'm just going to say here at this point

here where the two optic nerves are

connected all of this part right here

this whole thing is called the optic

chiasma and the optic chiasma is where

the right optic nerve and the left optic

nerve come together right near the

pituitary gland so this is right here

the pituitary gland okay now what

happens here the fibers from the

temporal Hemi retina which is receiving

it from the left visual field we said

anything from the left visual field will

go to the right eye okay so this is

going to cross means lock of the cross

it's going to stay on the same side so

is going to come down the right optic

nerve where the optic chiasma is it's

not going to cross it's going to stand

the same side and it's going to move

down this structure right here which is

called the optic tract and we're going

to stop right there okay so what is this

structure right here this long tube-like

structure here this whole tube like

structure here is called the optic tract

so this would be the right optic tract

what do you think this one is this is

the left optic tract and this is the

optic chiasma

okay now let's follow this nasal

hemorrhage huh well the nasal henry

retina is receiving information from the

right visual field well anything from

the right goes to the left so this is

got a cross so these fibers from the

nasal Heming retina it's going to come

through the optic nerve the right optic

nerve and it's going to cross at the

optic chiasma and go over here to the

opposite side it's going to come over to

what optic tract it's going to come over

here to the left optic tract and it's

going to come right to there and that's

what we'll stop at that point okay now

we understand this this should be a lot

easier now let's do this one

nasal hit me right now it's receiving

what it's getting hit from the last

visual field well if it's receiving

information for the left visual field

anything from the left has to go to the

right okay

well this is on the left that means it

has to cross over here so it'll come

down the left optic nerve but then

instead of going on the same side it's

going to cross over it's going to become

contralateral right and these fibers are

going to come over here

and they're going to move all the way

over here on this side and come right

there

okay so all the things that are coming

from the left visual field on the left

nasal Hemi ratney is going to be coming

from the left visual field it's going to

be taking that information on the right

optic tract and into this area that

we're going to talk about in a second

let's keep going temporal Hemi retina

it's going to be receiving information

from the right visual field right of the

left eye so it's going to be receiving

from the right visual field one new

thing from the right goes to the left

where are they on the left side of the

eye let's just keep it up see lateral so

these fibers here are going to come down

the left optic nerve it's not going to

cross at the optic chiasm it's going to

stay on the same side and move down the

left optic tract and then to this area

right here okay so these are your fibers

that are crossing and these are the

ipsilateral fibers so what do these

fibers right here called these fiber

gears that are staying on the same side

are your itsy lateral fibers these are

the ipsilateral fibers and these fibers

here that are crossing are called your

contralateral fibers contra lateral

fibers okay all right sweet deal now

that we know that let's keep it bring or

keep bringing it to where we're going to

go next so we already went from these

hmmm your retinues from the visual

fields we followed it down their optic

nerves the optic chiasm we folder down

the optic tract we see the FC lateral

fibers and we know the contralateral

fibers sweet deal what happens is from

this optic tract it's going to come to a

special area in the thalamus I'm

actually zooming in on the specific

nucleus on that ballast but let's say

pretend here that I have I draw kind of

like a little view of the thalamus it

has kind of like this like piece like

symbol a little bit and it kind of looks

like this and what happens is it has a

special nucleus coming off of it right

it has a special nucleus coming off of

it like this it's called the lateral

geniculate nucleus what I'm doing is I'm

taking the lateral geniculate nucleus

and just zooming it on it okay so this

right here is the thalamus

but a special nucleus of the thalamus is

called the lateral geniculate nucleus

I'm taking a large Nikolov nucleus and

zooming in on it okay so that we're

clear so this is lateral geniculate

nucleus it has a total of six layers six

layers so let's layer this one two three

four five six and the same thing over

here one two three four five six why am

I telling you this

because any epsy lateral fibers go to

two three and five layers so FC lateral

fibers within the lateral geniculate

nucleus are going to go to layers two

layers three and layers five so what

does that leave for the contralateral

the contralateral is left with going to

one four and six so then the

contralateral fibers will go to one four

and six okay so now it comes in to this

area right so I'm going to kind of make

these different because obviously the

same color but look here from this one

this is the contralateral so this one is

the contralateral fiber the

contralateral fiber goes to what one

four and six so if I were to do it let's

actually just make it a different color

from this point so that we're not

confusing this so now I'm going to come

from this contralateral fiber it's going

to be maroon it's going to give

connections to what for it's going to

give connections to six and it's going

to give connections to one then the

ipsilateral fibers are going to go to

two three and five okay and the same

thing is going to happen over here let's

say that I just for the sake of it I do

the same thing over here at the FC

lateral fibers and the contralateral

fibers over here so this one here is the

contralateral I'm going to keep the

contralateral maroon contralateral goes

to what it goes to six it goes to four

and it goes to one if see lateral fibers

are going to go to two three and five

now from this they're going to come out

of lateral geniculate nucleus so these

fibers are going to be coming out of the

lateral geniculate nucleus so the

terminate in this area some of the

fibers we'll talk about when we talk

about the pupillary light reflex some of

these fibers can actually go from the

lateral geniculate nucleus and into the

specific area of the midbrain there go

into the midbrain and there's two

structures in the midbrain that's a very

important one is going to be right here

called the superior colliculus it's

going to give off some branches that can

go there so some of the fibers can go

here to the superior colliculus so some

of the fibers can come to the superior

colliculus but a really really important

one is going to be just anterior to the

superior colliculus there's a very

important nucleus here called the pre

tectal nucleus so really important

nucleus here called the pre tectal

nucleus and we'll talk about this one

how it's connected with your basically

the constriction of the pupil okay so

that's the protective nuclei we're not

gonna talk about that now we're going to

talk about the rest of this pathway okay

I suppose you realize that some of these

fibers can go into the midbrain however

most of the fibers are going to continue

let's do this in pink now let's bring it

all nice and nice and pretty alright so

coming out of the lateral geniculate

nucleus there's going to be two types of

fibers one is going to run through the

temporal lobe and come to this area of

the occipital lobe so you see this right

here

all this structure that we have right

here this is representing the occipital

lobe so this is the occipital lobe and

this would technically be on the left

side and this is the occipital lobe and

this would be on the right side and

what's it separating them is what's

called the calcarine fissure right so

it's called the calcarine fissure right

here I'm not going to do that I was

remember it's the calcarine fissure all

right now some of the fibers from

ladder's nickel a nucleus move through

what's called the temporal lobe so some

of them move through an area of the

brain called the temporal lobe to go to

the occipital lobe some of the fibers

actually move through the parietal lobe

to come to

the occipital lobe so what's the other

one right here this would be the

parietal lobe and then the same thing

would happen over here so if we just

continuously do this because it's going

to be important that we make this very

very consistent here one's going to

remove through the temporal lobe to come

to the occipital lobe and one's going to

move through the parietal lobe to come

to the occipital lobe okay sweet

stinking deal this is the temporal and

this one right here would be the trial

the reason why I'm being so picky is

because these ones have different

they're different types of fibers these

are actually the ones that are moving to

the parietal lobe these are called the

superior retinal fibers they also call

it baram's loop so some bærum do musta

came up with it right so these superior

retinal fibers are actually also called

barrels and they're moving to the

parietal lobe these ones that are moving

to this temporal lobe are the inferior

retinal fibers so these are the inferior

retinal fibers and this is actually

called meyers loop so again some some

dude named meyers came up with that

right so again

inferior retinal fibers and this is a

part of meyers loop and it's important

because it talks about and when we get

to lesions right okay now these are

moving to deprive the lobe they'll come

to the occipital lobe and they'll go to

a specific area specific like part of

the occipital lobe and that specific

area of the occipital lobe is actually

called the striate cortex and the

striate cortex is basically the primary

visual cortex so the striate cortex is

basically the primary visual cortex this

is where the perception of these visual

stimuli become what we see okay so how

we perceive these different types of

images okay so that's an important thing

to know these fibers are coming to the

striate cortex of the occipital lobe

which is the primary visual cortex

where their perception of these visual

sensations are actually occurring all

right now that we've done that I need us

to apply some visual like correlations

that there are certain types of lesions

and different fibers here okay now the

only reason I'm saying that is to know

this is great but why do we need to

notice because we need to apply it to

clinical settings so let's say here that

I have a couple different lesions I'm

going to make it as simple as simple as

possible let's keep all the colors here

let's do it in like this maybe we'll do

in purple here will represent the lesion

by purple I'll say there's a lesion here

so that's leaves you're number one okay

then let's say that there's a lesion

right here so there's a lesion right

here this is leisure number two then

let's say that there's actually going to

be a lesion on the outside here and

outside here at the same time so let's

say that this is lesion number three

then let's say that we have a lesion

that's occurring right here leisure

number four and then we'll have a lesion

here like lesion number five lesion six

and then what happens if we had damaged

the whole thing lesion seven and the

last thing is what if we develop some

type of damage to the occipital lobe and

that will be lesion eight so eight total

lesions is what we're going to talk

about here okay here we go if the right

optic nerve is damaged let's do our

visual fields here let's get our little

visual fields here keep it super super

simple here here's our visual field for

the right eye so we're gonna have two

visual fields here one right there for

the right eye one right there for the

left eye and we'll separate into the

left visual field and right visual

fields so again this is for the left eye

this is for the right eye if this right

here is damaged

this right here is damaged this optic

nerve then I'm losing what I'm losing

the certain types of visual sensations

from the right visual field of the right

eye

okay so right visual field of the right

eye it's gone I have no vision in this

area so let's go ahead and shade that in

this whole thing go on

I got no vision there I developed some

scotoma right there I lose all my vision

in that that visual field

then any of the information all the

visual sensations that are coming from

the left visual field of the right eye

that's gone - alright see ya

see you later that's it I lose all the

information from these two visual fields

of the right eye

what do I develop I develop mono ocular

blindness which side right sided mono

ocular blindness so what is this called

right here mono ocular blindness or an

obeah so we can say that this is right

side mono ocular blindness or an opium

okay simple of that and this would be

lesion number one so Louise you're

number one if you damage the optic nerve

you're going to have complete right side

of the eye mono ocular blindness no

vision there second one let's say that

you develop a pituitary tumor and it

compresses the medial part here of the

optic chiasma it's compressing the

contralateral fibers here so let me make

two visual fields here okay so this one

is going to be again this is for your

left eye and this is for your right eye

well it's going to be affected here if I

damage the contralateral fibers what

does that mean okay let's follow this

one over your nasal Hemi ratney I'm

losing the visual sensations from the

left visual field of the left eye that's

gone

see you later they're like hey let's do

this in a different color here like this

this is gone okay so I lose that sight I

lose my temporal visual field or the

left visual field of that left eye right

then what I'm also damaging these fibers

and if I damage these fibers this is

picking up information from the right

visual field of the right eye so now

this is gone so I'm losing my temporal

vision on the right eye because I'm

losing my vision and both the visual

fields two temporal fields right the

temporal fields this is called they got

a heck of a name for this one they call

it by temporal Hemi a no Pia or enough

and they not hemianopsia you can even

say like that

so bitemporal hemianopia

okay that's done what about three okay

let's say that there's some type of you

know the internal carotid arteries kind

of run nearby here

so there's actually internal carotid

arteries that runs very very near this

optic chiasma right here let's say that

for some reason these guys develop like

an aneurysm right and they compress

these outer parts here be careful you

have an aneurysm of both of them and

it's actually compressing both these

fibers what fibers the ipsilateral

fibers so now let's draw your two visual

fields here this is four three okay this

is your left eye this is your right eye

okay if it's damaging the ipsilateral

fibers you're going to lose information

from the nasal field of the left eye and

if you're damaging this FC lateral fiber

you're going to lose the nasal field of

the right eye

well that's by temporal this is going to

be by nasal by nasal hemianopia will

turn me over and tickle me twisted look

at that that's called by nasal Hemi a

Nokia or in nobs synopses right so by

nasal hemianopia is the third type of

lesion

so I'd be number three so this is number

three here this was number two and this

was number one

okay now off the number four if you lose

number four let's make our visual fields

here and I'll do it like this again left

eye and right eye left and right visual

fields

bye damage these bad boys all this right

optic tract let's follow it the right

optic tract let's follow this one first

okay come over here come over here come

over here

okay Mazal heavy right knees not going

to work so I'm gonna loop my would lose

the left visual field of my left eye so

last visual field of the left eye gone

that's gone okay follow this one if we

follow this one follow this one for this

one we go over to the temporal Hemi

retina which I'm losing it from the

nasal side of my right eye that socks

and if I loose it from the nasal side of

my right eye what would I call this one

they got a heck of a name for this one

all right

it's a little tight it's a tiny bit

confusing but I want you guys to

remember remember we said that this was

the temporal and the nasal nasal

temporal right we also said that we

could say that this is the left visual

field in the right visual field and left

eye left visual field of the right eye

and right visual field of the right eye

what did I lose I lose both of my left

visual fields of both eyes so because of

that they call it left homo

nyam is Hemi and Opia why not

so that is the fourth type of lesion and

you would have the same thing at that

hashing on the left optic tract except

to be right homonymous hemianopia so

again this is lesion number four

it's called left homonymous hemianopia

now let's say that we get back here we

get back here now these are the these

are the frackers these are the one that

can be a little bit confusing here let's

say that I do number five here right so

now I damage this part the actual what

loop the baram's loop which is called

the superior retinal fibers before I

move on let me make a mini little

diagram here so that I can really really

make sense of this we can split the

visual fields up like we did over there

but we can actually if we really want to

be very very specific let's say I make

here this is my left visual field my

right eye left eye sorry left eye right

eye

remember how we split it into a left

visual field and a right visual field

for both of them guess what we can split

it into a upper left upper right lower

left lower right okay now let's say

everything up above this part that I

have in blue this is all the superior

part right so this is the superior part

of the retina all this down below is the

in fear red now when we're talking about

the superior etta no fibers okay now I'm

looking at the eye like from my eyes

like imagine here I have my eyeball like

this I'm actually fixing my eye and

looking straight down like this into the

eyeball okay let's pretend for a second

though that I look at it like this now I

take this eyeball here and let's say up

here I have my superior part of the

retina and then down here I have the

inferior part of the retina the superior

part of the retina is getting hit with

light rains that's coming from the lower

visual fields and then the inferior

retina is getting hit with light range

that's coming from the superior visual

field it's frickin crazy I know but I'm

sorry that's how it works

so now when we make this one we have to

make it like this here's left eye right

eye we have to split it like this but

then into fours okay superior quadrant

in

your quadrant okay okay

now let's let's think about this if this

suit we damaged this right side the

right superior retinal fibers if the

right superior retinal fibers are

damaged remember anything from the right

side is coming from the left eye or the

left visual field so again anything

that's coming from this is coming from

the left visual field anything that's on

the right eye is coming from the left

visual fields so want to make sure that

we get that completely clear if this is

damaged the superior edge no fibers then

I'm losing the vision within the

inferior visual field on the left side

okay so we already know that I'm losing

the actual left visual field that's

already clear does anything from the

right eye is picking up information from

the left visual fields so all of this is

gone the left side

but remember superior at no fibers only

pick up the information from the

inferior visual field so really we're

only losing this part here and we're

only losing this part here so because

I'm losing vision within the lower

quadrant of the left visual field we

call this what this one's a heck of 1 to

left inferior quadrant Hemi and Opia

okay so left inferior quadrant

hemianopia and it's because we're losing

our vision within the left visual field

and in the inferior plane okay then if

we did a lesion here in the sixth one

right so we said that we damage this six

one here so let's actually do this one

up here so physically we're running out

of room up there so let's do the six one

up here so the sixth one we're going to

damage right here okay so let's make our

visual fields same thing we got to make

this into four parts we're going to cut

it up like this cut them up like this in

fear retinal fibers and this is from

this is actually on the left side so

this is the left inferior retinal fibers

so that means that it's receiving

information from the right visual field

okay so we already know it's right

visual field that are being affected

done okay and again this is left eye and

this is right eye we know that the right

visual fields are going to be affected

but we know it's the inferior part of

the retina that's being affected if the

inferior part of the retina is being

affected we're losing vision in the

superior plane so now what's going to

happen we're losing the right visual

fields but on the inferior the superior

plane so now you're losing this part

here what is this one called this is

called right superior quadrant Hemi and

Opia

okay that's that one so right superior

quadrant hemianopia and if you get this

one then you should be able to get the

same thing if I damaged this other side

okay it would just be the exact opposite

maybe left superior quadrant hemianopia

if I damage this soupy retinal fibers of

this side on the left side then I'd have

right inferior quadrant hemianopia the

same thing okay

holy sweet goodness now we have this

seventh one here seventh one if I damage

this whole thing you know I never even

told you what the heck these pink

structures are I'm so sorry about that

these pink structures here all of these

this one here this one here from both

sides

they're called optic radiations they're

called optic radiations so these

superior retinal fibers and in

theoretical fibers are make up what's

called the optic radiations or you can

call this the Janicki low calcarine

tract and the reason why it's coming

from the Janicki body to the calcarine

fissure okay so these optic radiations

let's say that I damage the right optic

radiation so I damage my right optic

radiations okay right optic radiations

bricking going okay so if that's damaged

let me get rid of this right here so I

can make room here same thing let me

write draw this right here this right

here but because not affecting it's a

losing if you're losing both the quadric

so we're just going to make it to the

boxes here if I damage this one and I

damage this one what do I remember

anything that's on the right side I'm

losing it from the left visual fields so

if I'm losing it from the left visual

fields then what must be happening here

I'm losing it from both the superior and

for your planes so that means I'm losing

all of the information from the left

visual field of the left eye and the

left visual field on B right eye what do

we call this one if you remember doesn't

it seem very very familiar it looks just

like this one right over here what is

this one over here called

this one was called left homonymous

hemianopia it's the exact height

vaccine-type here so

is called left homonymous hemianopia

one and we're thankfully done here let's

say that you damage a specific part of

the occipital cortex you know there's

two arteries that are supplying the

occipital lobe here there's what's

called the posterior cerebral artery

which is a part of the Circle of Willis

and there's another one here called the

middle cerebral artery which is actually

a branch of the Circle of Willis let's

say that you develop some type of most

common cause here some type of lesion

with the unlocks epital lobe is you

develop a lesion here within the

posterior cerebral artery you still have

blood that can supply the occipital lobe

from the middle cerebral this is the

middle cerebral artery you still can get

blood to the occipital lobe now there's

a specific area in occipital lobe that

picks up very very acute vision that is

within the macula of the eye okay so

there's the macular region of the

occipital lobe if the post a cerebral

artery is occluded you might affect the

blood flow to the macular region of the

occipital lobe well because we have

these middle cerebral arteries they're

still going to give blood to the macula

so what happens here something really

freaking weird is because you spared the

macula by giving a blood flow from the

middle cerebral artery you spared the

macular region the occipital lobe then

whenever you do their visual fields so

again here's the left here's the right

eye split up their visual fields here

into left and right there's something

really thing a weird here that we can

actually include into this I can put a

circle here and this circle here is

representing the center of that part in

the eye you know how we have the macula

lutea where the fovea centralis is the

highest concentration of cones what

happens is if you can actually spare

that macula because the posterior artery

is occluded but the middle cerebral

artery is still getting blood flow to

this area this area of the macula is the

this area of the occipital lobe where

the macular impulses are coming to that

will be spared but again everything is

on this right side so if the right part

except a little bit of damage anything

from the left visual field will be lost

so what am I going to lose

I'll lose this part of the left visual

field and I'll lose this part of the

left visual field but guess what I will

not lose I won't lose this specific area

right there which is actually called the

macula region so this is called it looks

like oh isn't this left homonymous

hemianopia yeah this right here is

called left homo 9ms hemianopia but with

sparing of the macula with sparing of

macula

okay that's the whole purpose of this

all right so in this video we talked

about the visual field processing we

talked about the visual field processing

we talked about the actual visual

pathway and we talked about associated

lesions that could develop within the

different parts of this visual pathway

guys I really hope all of this made

sense I really really really do hope

that you guys did enjoy it and I hope it

helped if it did please hit the like

button comment down the comment section

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alright engineers as always until next

time