Vision + Visual Field

Question 1

What happens when light enters eye

Answer 1

Travels through all layers of retina to reach rod and cones (photoreceptor)
Transduction occurs to convert light -> chemical
Travels back and synapse at nerve fibre layer
Joint optic nerve to generate AP (photoconduction)

Question 2

What is fovea centralis

Answer 2

Area packed with cone cells for max visual acuity
Located within the macula
High concentration of cone cells
Exposed so don’t have to pass through all layers of retina
Eyes will move to focus on this

Question 3

What is the macula

Answer 3

Small area at centre of retina for central field of vision

Contains highest conc of cone cells

Question 4

How do rod and cone cells work in the dark

Answer 4

At rest

Depolarised by open Na / Ca) channel

Question 5

What do rod and cone cells do different

Answer 5

Different visual pigment
Rhodopsin pigment in rods = low light
Opsin in cones = daylight / colour

Question 6

Colour blindness

Answer 6

Defect in cone cells or pathway to brain

Question 7

What happens when light enters aye

Answer 7

Changes vit A in pigment to all-trans-retinal (ActivateD)
Molecule can’t fit into rod / cone
Splits = bleaching and activation of visual pigment (rhodopsin / opsin)
Picked up and changed back to original but only if have diet vitamins A

Question 8

What is activated rhodopsin

Answer 8

No vit A present 11’cis-retinal

Question 9

What happens when activated

Answer 9

Causes channels to close
Hyperpolarisation
AP forms and travels to optic nerve in nerve fibre layer

Question 10

What happens if vit A deficiency

Answer 10

Can't see in the dark
Unhealthy conjunctival and cornea
Bitots spots (triangular silver foam) in conjunctiva
Ulceration
Corneal melting + opacification

Question 11

What is refraction

Answer 11

Bending of light rays to form a sharp image on retina when changing from one optic medium to another

Question 12

What are main mediums

Answer 12

Cornea + lens

AH / VH = refract slightly

Question 13

When do errors occur

Answer 13

If mismatch in bending

Question 14

What happens if object close

Answer 14

Eye needs to bend more to focus

Lens becomes thicker

Question 15

If object >6m

Answer 15

Light is parallel

Question 16

If <6m

Answer 16

Divergent rays so bend

Question 17

What is convex

Answer 17

Makes light converge (bend in)

Question 18

What is concave

Answer 18

Makes light diverge (bend away)

Question 19

What is accommodation

Answer 19

Bending light to focus on far off or near objects

Question 20

What happens

Answer 20

Lens thicker to focus on close object
Pupil constrict for sharp focus
Eyes converge - MR (III)

Question 21

What are intrinsic ocular muscles and nerve

Answer 21

Pupillary constrictor - para III - Ach

Pupillaey dilator - sympathetic - NA

Question 22

What happens if increased light and what is the mechanism

Answer 22

Pupil constrict
Light on retina
Travels to optic nerve -> chiasma -> tract
Do not go to LGB
Go to mibrain and synapse on III on both sides

Question 23

What happens if decrease

Answer 23

Pupil dilates

Question 24

What are extrinsic ocular muscles

Answer 24

Superior rectus
Inferior rectus
Lateral rectus - CN6
Medial rectus
Superior oblique - CN4
Inferior oblique
All other CN3

Question 25

LOOK AT EYE

Answer 25

OK

Question 26

Where is L half of visual field seen

Answer 26

R side of retina

Question 27

What is the pathway of visual field

Answer 27

Optic nerve -> optic chiasma Medial fibres (nasal) cross to opposite side Lateral stay the same Travel in optic tract and synapse in LGB of thalamus Optic radiation travels through internal capsule Goes to visual cortex in occipital lobe

Question 28

What does process at chiasma mean

Answer 28

Optic tract contains fibres from lateral half of ipsilateral and medial from contralateral so ALL fibres from opposite half of visual field = optic tract L visual field = R optic tract

Question 29

What does L side of brain receive

Answer 29

L visual field of both eyes

Question 30

What happens if R optic nerve damage

Answer 30

No vision in R eye | Direct reflex is absent but indirect will remain intact

Question 31

What happens if optic chiasm disrupted due to pituitary tumour

Answer 31

Affects temporal vision (nasal fibres) as they cross over at chiasma Bitemporal hemianopia

Question 32

What happens if optic tract or radiation is damaged

Answer 32

One side of visual field is lost in both eyes Contralateral homonymous hemianopia If R tract = L visual field lost in both eyes

Question 33

What happens if occipital cortex is damaged

Answer 33

Contralateral homonymous hemianopia with macular sparing

Question 34

If optic tract lesion in parietal lobe

Answer 34

Inferior qaudranopia

Question 35

If lesion in temporal lobe

Answer 35

Superior quadranopia

Question 36

How do you remember

Answer 36

PITS | In opposite side of Brain

Question 37

What type of bitemporal hemianopia if pituitary

Answer 37

UQ as inferior chasm compressed

Question 38

What type of bitemporal hemianopia if craniopharyngioma

Answer 38

LQ as superior chasm compressed

Question 39

What are causes of visual field defects

Answer 39

``` Ischaemia - TIA / migraine / stroke Glioma Menigioma Abscess AV malformation Drugs ```