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Ophthalmology > Vision + Visual Field > Flashcards

Vision + Visual Field Flashcards

1
Q

What happens when light enters eye

A

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)

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2
Q

What is fovea centralis

A

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

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3
Q

What is the macula

A

Small area at centre of retina for central field of vision

Contains highest conc of cone cells

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4
Q

How do rod and cone cells work in the dark

A

At rest

Depolarised by open Na / Ca) channel

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5
Q

What do rod and cone cells do different

A

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

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6
Q

Colour blindness

A

Defect in cone cells or pathway to brain

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7
Q

What happens when light enters aye

A

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

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8
Q

What is activated rhodopsin

A

No vit A present 11’cis-retinal

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9
Q

What happens when activated

A

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

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10
Q

What happens if vit A deficiency

A 
Can't see in the dark
Unhealthy conjunctival and cornea
Bitots spots (triangular silver foam) in conjunctiva
Ulceration
Corneal melting + opacification
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11
Q

What is refraction

A

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

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12
Q

What are main mediums

A

Cornea + lens

AH / VH = refract slightly

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13
Q

When do errors occur

A

If mismatch in bending

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14
Q

What happens if object close

A

Eye needs to bend more to focus

Lens becomes thicker

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15
Q

If object >6m

A

Light is parallel

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16
Q

If <6m

A

Divergent rays so bend

17
Q

What is convex

A

Makes light converge (bend in)

18
Q

What is concave

A

Makes light diverge (bend away)

19
Q

What is accommodation

A

Bending light to focus on far off or near objects

20
Q

What happens

A

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

21
Q

What are intrinsic ocular muscles and nerve

A

Pupillary constrictor - para III - Ach

Pupillaey dilator - sympathetic - NA

22
Q

What happens if increased light and what is the mechanism

A

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

23
Q

What happens if decrease

A

Pupil dilates

24
Q

What are extrinsic ocular muscles

A 
Superior rectus
Inferior rectus
Lateral rectus - CN6
Medial rectus
Superior oblique - CN4
Inferior oblique
All other CN3
25
Q

LOOK AT EYE

A

OK

26
Q

Where is L half of visual field seen

A

R side of retina

27
Q

What is the pathway of visual field

A

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

28
Q

What does process at chiasma mean

A

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

29
Q

What does L side of brain receive

A

L visual field of both eyes

30
Q

What happens if R optic nerve damage

A

No vision in R eye

Direct reflex is absent but indirect will remain intact

31
Q

What happens if optic chiasm disrupted due to pituitary tumour

A

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

32
Q

What happens if optic tract or radiation is damaged

A

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

33
Q

What happens if occipital cortex is damaged

A

Contralateral homonymous hemianopia with macular sparing

34
Q

If optic tract lesion in parietal lobe

A

Inferior qaudranopia

35
Q

If lesion in temporal lobe

A

Superior quadranopia

36
Q

How do you remember

A

PITS

In opposite side of Brain

37
Q

What type of bitemporal hemianopia if pituitary

A

UQ as inferior chasm compressed

38
Q

What type of bitemporal hemianopia if craniopharyngioma

A

LQ as superior chasm compressed

39
Q

What are causes of visual field defects

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

Ophthalmology (10 decks)

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