The Eye And Visual Pathways

Front 1

what is the neural retina

Back 1

typically refers to three layers of neural cells (photo receptor cells, bipolar cells, and ganglion cells) within the retina

while the entire retina refers to these three layers plus a layer of pigmented epithelial cells

Front 2

what does the neural retina develop from

Back 2

developsas part of the neural tube nso is a part of the brain, the optic nerve hence isa central nerve.

Front 3

where does the neural retina end?

Back 3

The neuralretina ends at the ora serrata (serrated edge), there is then (on theillustration) a black structure that goes over the ciliary bodies andback of the iris (ora serrata).

Front 4

what does the neural retina detect, and how does it send afferents to the brain

Back 4

The neural retina detects light and contains afferents,which go out and form the optic nerve, carrying signals back to the thalamus.

Front 5

what types of cells does the neural retina have to allow it to detect light

Back 5

havephotoreceptors here. Cones are for daylight vision, and rods are for ‘scotopic’(night time) vision

Front 6

how does the retina send afferents to the brain

Back 6

We have afferents with ganglion cells.

Axons run across thesurface of the retina.

The gap is bridged by inter-neurones in the inner nuclearlayer.

Front 7

what is the fovea centralis

Back 7

a small depression in the retina of the eye where visual acuity is highest. The centre of the field of vision is focused in this region, where retinal cones are particularly concentrateq

Front 8

what is the visible which part of the eye made up of

Back 8

made up of collagen. Tough and flexible.

Front 9

what is the uveal tract of the eye and what does it contain

Back 9

The uveal tract is a layer of tissue located between the outer layer (cornea and sclera) and the inner layer (the retina) of the eye.

The front portion (anterior) of the uveal tract contains the iris, and the back portion (posterior) of the uveal tract contains the choroid and the stroma of the ciliary body

Front 10

how is the cornea arranged

Back 10

collagen are v organized, and gluedtogether with proteoglycans. So have a transparent window through which thelight can pass

Front 11

the eye isnt made of solid structures. they are very flexible. so, how is the shape of they eye maintained

Back 11

shape of eye is maintained by thecontents. In posterior Segment of the eye you have the vitreous humour.In the anterior segment of the eye you have the aqueous humour.

Shape of eye is maintained bypressure created by the aqueous humourbeing produced and drained.

Allows eye to maintain its globular shape.

Front 12

learn

Back 12

.

Front 13

what are the characteristics of the choroid layer of eye, and why is it important

Back 13

Very vascularized layer that produceda very rapid flow of blood past the photoreceptors.

It actually provides the o2and glucose and other demands for the outerpart of the retina.

Front 14

The cillary body of the eye contains two different compartements. what are these.

Back 14

1 – muscle that controls the shapeof the lens via the suspensory ligaments on either side.

2 – tissue thatproduces the aqeous humour.

Front 15

what is the optic nerve made up of

Back 15

Made up of the axons of retinal ganglioncells whichflow across surface ofretina.

It is covered in the 3 layers of meninges (pia matter, arachnoid matterthen dura matter).

Front 16

inner layer of the eye has two main regions. what are these

Back 16

neural retina &Retinalpigementepithelium

Front 17

what is the retinal pigment layer

Back 17

The latter is a single layer of pigmentepithelial cells.

Front 18

how are the retina &Retinalpigementepithelium joint

Back 18

The two layers aren’t ever joinedtogether v strongly.

They are parially glued together by proteoglycans.

The pigment epitheliumpump fluid out from the gap between them creating some suction. It is thissuction and glue that holds the retina to the back of the eye .

If that suction gives way, theretina may float free from the pigment.

Front 19

what does the neural retina do

Back 19

1 -The neuralretina detects light by use of rods and cones

2 - totransmit the information they detect to the brain by the afferents that then go out and form theoptic nerve.

Front 20

what are rod photoreceptors

Back 20

receptors that detect light in night vision,also called scotopic vision (work best in dim light).

Front 21

what are cone photoreceptors

Back 21

receptors that detect light.

for daylightvision (work best in bright light)

Front 22

how does the neural retina transmit information it detects to the brain

Back 22

The axons of theganglion cells (in the inner layer of the retina) run over the surface of the retina and head to the optic nerve.

Front 23

what does the inner nucleur layer of the eye contain

Back 23

containsinterneurons which lay inbetween the photoreceptors to the ganglion cells.

Front 24

what is the importance of the bipolar interneuronem and where is is it situated

Back 24

in the innernuclear layer,

thebipolar interneurone that is in the middle of the two cones. Theseconnect the photoreceptors to the ganglion cells.

Front 25

what is the ganglionic cell receptive feed

Back 25

Therays of the visual image that enter our eye that are detected by cones, and form the retinal receptive field for this ganglion cell

Front 26

why is it adaptive for the cones to converge their input into one single ganglion cell?

Back 26

When lightenters the eye, it has to pass through the vitreous and the multiple layers ofthe retina before it reaches the cones. In fact it is the outer-portion of thecones which actually detect the change in illumination.

light that hitsthe retina being detected is blurred because it has had to pass through theseouter layers first.

These pool ofcones will converge input onto a single ganglion cell so make sense of multiple blurry images

Front 27

what is the peripheral and central retina

Back 27

Front 28

why is peripheral vision poor

Back 28

the fact thatthe cone photoreceptors in the periphery are large and spaced widely apart totry gather as much of this scattered/blurred light

cones in periphery have large receptivefields

-> Thesecones gather this blurred light and converge it onto single ganglion cells andthus all of this info of this region of scattered light is brought to one cellto transmit the info

Front 29

within the central retina, we have the Macula Lucida (area of yellow pigment). what is the importance of this

Back 29

Within themacula lucida is the fovea centralis, this is a very specialised and small areaof the eye. The fovea has no overlying blood vessels or capillary bed.

Front 30

why is the fovea so important/ why does the fovea allow us to avoid blurry vision in the cenral retina

Back 30

The fovea isspecalised because it contains a small region, only 0.35mm across where theganglion cells and interneurons have been pushed back and halted to leave afoveal pit.

This directlyexposes the photoreceptors and means that light that passes into the eye andvitreous does not have to pass through multiple layers first and thus not besubject to getting scattered.

This is the onlypart of the eye where vision is very well focused/ resolution and it visualisesabout the size of your thumbnail at arms-length.

Front 31

how do the characteristics of cones in the fovea and the peripheral retina vary

Back 31

cones in thefoveal pit are very slender and thus a huge number are packed in together(150,000mm2).

Eachphotoreceptor then synapses onto a single ganglion cell, so there is noconvergence.

This means the fine image (because no scattering!) detected byeach single photoreceptor is signaled to a single ganglion cell so there is no“noise” added to the fine image and instead is signaled back to the braincompletely as the fine image.well focused

Front 32

how is the fovea specialised for high resolution

Back 32

-> Overlyinglayers and blood vessels are absent so the image is well focused/not scattered

-> The foveaonly contains cone photoreceptors which are narrow and closely packed

-> Thesignals from photoreceptors are kept separate

Front 33

what happens to light hitting they eye (externally)

Back 33

someof these rays will hit your cornea and pass through.

Someof the rays that pass through will be blocked by the iris

others will passthrough the pupil and these will be brought into focus/further refracted by thelensin

Front 34

what has the primary role in focusing light rays

Back 34

It is the corneathat refracts the light the most and hence is primary responsible for focusinglight rays.

Howeverthe cornea is fixed in its refractory ability

Front 35

what structure of the eye accomodates focusing on near or far items

Back 35

the lens

Front 36

what is the punction of the iris

Back 36

The iris controlsthe amount of light that enters the eye via the pupil.

Front 37

why does the pupil dilate and constrict

Back 37

If the pupil wasa pinpoint, then the image would be clearly focused on the back but it would bevery dim as hardly any light would get through.

The larger thepupil the more light enters in and will hit the outside of the lens which isnot as good at focusing the image and it leads to more blur.

Front 38

what muscles control the optics of the eye

Back 38

1 - The sphincter pupillae is a ring muscle and when it contracts it makes the pupil smaller

2 - ciliary muscle-a ring shaped muscle going around the front part of the eye.

3 - dilator pupillae,when the muscle contracts it pulls the pupil open

Front 39

what is the role of the sphincter pupillae muscle

Back 39

The sphincterpupillae is a ring muscle and when it contracts it makes the pupil smaller.

Whensphincter pupillae is relaxed, the pupil is large and dilated

Front 40

how are the sphincter pupillae controlled

Back 40

Under thecontrol of the short ciliary nerves which are parasympathetic nerve fibres,they use Ach as their neurotransmitter.

The shortciliary nerves come from the ciliary ganglion, a parasympathetic

Thepre-ganglionic fibres going into this pathway of contracting sphincter pupillaeare actually primarily driven by the retina itself! This is thedirect/consensual light reflex!

Front 41

what nerve carriesparasympathetic pre-ganglionic fibres to the ciliary ganglion?

Back 41

CN III

(oculomoter nerve)

Front 42

what is the light reflex

Back 42

Inthe retina we have the retinal ganglion cell which will be activated if thereis illumination of that retina

Signalsfrom that ganglion cell -> sent to pretectal nucleus -> sends axons to Edinger-Westphalnucleus -> sends preganglionic parasympathetic fibres to cilliary ganglion.

ciliary ganglion axons synapse onto postgangionic short ciliary nerves -> release of Ach onto the sphincter pupillae so eye constricts

Front 43

why does illumination of one eye lead to constriction in both eyes

Back 43

pretectalnucleus neurones synapse onto both sides of the Edinger-Westphal nucleus, soboth parasympathetic pathways get activated!

Front 44

what is the function of the dilator pupillae.

what does this muscle react to

Back 44

when the musclecontracts it pulls the pupil open

This dilation isbrought about by the long ciliary nerves which innervate dilator pupillae. Thisis a sympathetic pathway.

When the eyedilates it is NOT in response to a decrease in light rather it is due to strongemotional drive. For example, fear, love.

Front 45

what is the characteristics of a normal eye

Back 45

thelength of their eye is perfectly matched to the strength of their optics

Front 46

how does a normal eye react to seeing something far away

Back 46

If the person islooking at something very far away, the light rays will enter into their eyenear enough parallel and only need a little extra refraction in the lens to getthe image onto the retina (so lens will be flattened).

Front 47

how does a normal eye react to seeing something close

Back 47

If an individualwants to look at an object close to them the light rays will be diverging morethus more refractive power is needed to bring the rays together. The lens willbe made fatter and this will refract the light nicely onto the retina and it iswell focused

Front 48

what is myopia

Back 48

theoptics of their eye are simply too strong, the refractive power is too much forthe length of their eyeball.

so individuals are short-sighted.

Front 49

how does a myopic eye react to seeing something close

Back 49

The individualwith a myopic eye will look at something close and lens will bulge as lightrays are more divergent.

However, the power of the optics is too strong andthus the light rays and image will be refracted so strongly it will focus infront of the retina.

This is what amyopic eye is, when objects are focused in front of the retina.

canhowever still focus on close objects by flattening out the lens for closeobjects and thus reducing the refractive power to get the image onto the retina.

This flattened lens would usually only be for distant objects, so person isessentially using long distance vision to view close objects.

Front 50

how does a myopic eye react to seeing something far away

Back 50

However as themyopic eye has compensates by using long distance vision to look at closeobjects.

With far away objects the lens cannot be made sufficiently more flatto get the image on the retina. The optics are still too strong. Hence theimage will focus in front of the retina

Front 51

how can you fix myopic lems

Back 51

The way to fixmyopia is with a concave (negative) lens.

This will diverge the rays a bit moreand thus weakens the overall optics of the eye so the image will be able tofocus onto the retina.retina.

Front 52

what are the characteristics of a hypermetropic

Back 52

the optics of apersons eye are too weak and the refractive ability of their eye is too weakfor the length of their eye.

Then the eye is hypermetropic, this is where theimage focuses behind the retina as the optics are not powerful enough to focusit properly!

being long-sited

Front 53

what is meant by the optics of the eye

Back 53

the basic optic function of the eye is to form an image of whatever object being looked at (fixated on) on the retina.

This image formation is done by the combination of the cornea and the lens which behaves like a convex lens

Front 54

how does a hypermetropic eye respond to seeing things far away

Back 54

longdistance image with its rays very straight anyway, cannot be focused enough.

lenscan compensate and adapt in order to focus far away objects by bulging out andincreasing the refractive power (as if the object were close!)

This brings theobject into focus on the retina4

Front 55

how does a hypermetropic eye respond to seeing things that are close

Back 55

The problem thenarises with near objects, here the light rays are much more divergent thusrequiring more refraction by the lens.

However the lenshas already refracted strongly for distant objects and cannot get any more fatand has reached its maximum refractive power.

This level it is not enough andthe image will be focused after the retina.

Front 56

how can hypermetropia be corrected for functional vision

Back 56

Hypermetropiacan be corrected with a convex (positive) lens that increases the refractivepower of the overall optics.

This helps bring the rays together and gets themfocused onto the retina

Front 57

why does vision decrease with age

Back 57

the lens has avery little capacity to regenerate and thus can fail with age.

Front 58

why does the eye have such little ability to regenerate

Back 58

that in order tohave such a transparent structure it needs to be made up of cells that containvery few organelles. Due to this they have very little regenerative capacity

Front 59

why do many middle aged people require lenses for both short and long distances

Back 59

Inmiddle age, the lens becomes stiff and stops responding to changes in theciliary muscle.

Because of this focus becomes fixed (presbyopia) and theindividual may need two pairs of glasses to see properly both long and shortdistance.

Front 60

when may an individual develop a cataract.

how can this be resolved

Back 60

In old age or inpathological conditions things can get worse, the lens can become opaque, thisis a cataract.

The only solution here is to take it out and replace it with anartificial lens.

Front 61

what is the primary visual pathway.

what other pathways run alongside it

Back 61

pathwayis the pathway from the eye, to the thalamus to the primary visual cortex inthe occipital lobe

Alongside thisprimary visual pathway we also have another pathway that is associated withreflexes and orientating responses.

Front 62

what is the role of the superiorcolliculi

Back 62

integrating sensory information (visual, auditory, somatosensory) into motor signals that help orient the head toward various stimul

involved inreaching movements, turning the head and eyes towards a stimulus requiringattention and navigating in locomotion.

Front 63

where is the pathway for visual perception

Back 63

start of at the retinal ganglion cells -> project back to the lateralgeniculate nucleus (LGN) in thethalamus -> From here axons go back to the to calcarine sulcus (which is in the primary visual cortex in the occipital cortex)

Front 64

what is the optic radiation

Back 64

The optic radiation (also known as the geniculocalcarine tract, the geniculostriate pathway, and posterior thalamic radiation) are axons from the neurons in the lateral geniculate nucleus to the primary visual cortex.

Front 65

where does light coming from the left visual feild hit (in both eyes)

Back 65

Light comingfrom the left visual field will fall onto the right side of our retinas, inboth eyes. In the right eyeit will fall onto the temporal retina, in the left eye it will fall onto thenasal retina.

Front 66

where does light coming from the right visual feild hit (in both eyes)

Back 66

Light comingfrom the right visual field will fall onto the left side of our retinas, inboth eyes. In the left eyeit will fall onto the temporal retina, in the right eye it will fall onto thenasal retina.

Front 67

how is left visual field information processed

Back 67

As left visual field information will be processed in the right hemisphere:

Right temporal fibre (from Right eye temporal retina) does not need to cross the optic chiasm as it is on the same side as the hemisphere the information will be processed.

Left nasalganglionic fibres (from left eye nasal retina) will be carrying information from theleft visual field (red) and will be processed in the right hemisphere andtherefore need to cross over at the optic chiasm to get to the right hemisphere.

Front 68

how is right visual field information processed

Back 68

As right visual field information will be processed in the left hemisphere:

left temporal fibre (from left eye temporal retina) does not need to cross the optic chiasm as it is on the same side as the hemisphere the information will be processed.

right nasal ganglionic fibres (from the right eye nasal retina) will be carrying information from the right visual field and will be processed in the left hemisphere and therefore need to cross over at the optic chiasm to get to the left hemisphere.

Front 69

what happens of there is damage in front of the optic chiasm

Back 69

thedamage is independent of the two pathways.

if an optic nerve is damaged, it affects only the visual field of that eye.

So in otherwords there will be different deficits in the two eyes.

Front 70

what happens of there is damage in behind the optic chiasm

Back 70

Behind the chiasm axons from a matching part of the 2retinae lie close together to any lesion will take out a matching part of thevisual field that is being projected back from the 2 eyes.

If it matches inboth eye you know it is from behind the chiasm.

Front 71

Primaryvisual pathways have a pathway associated with reflexes.

where are the nuclei involved in this reflex

Back 71

Allnuclei involved in this kind of movement of the eye are down in the brain stem,the biggest and most prominent is the superior colliculus

Front 72

what defect can be seen here

Back 72

Inthis case, there has been loss of the left visual field in the right eye dueto a detached retina

Front 73

what is glaucoma

Back 73

a condition of increased pressure within the eyeball, causing gradual loss of sight.

Front 74

what may a lesion of one optic nerve cause

Back 74

A lesion of one optic nervecauses monocular blindness in the corresponding eye (as the nerve contains allthe fibres for the visual field of that eye)

Front 75

what may be the effect of a lesion of the optic chiasm

Back 75

- A lesion of the optic chiasmadestroys crossing nasal fibres (nasal fibres look at the temporal field on bothsides) this leads to a bitemporal hemianopia

Front 76

what is hemianopia

Back 76

blindness of half the field of vision

Front 77

what may a lesion of the optic tract cause

Back 77

A lesion of the optic tract(which is carrying axons for the right OR left visual field only) will lead toa contralateral homonymous hemianopia (contralateral as other side

e.g. rightoptic tract will lead to left hemianopia, homonymous as in both eyes,hemianopia as in half visual field loss)