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Year 2 Neuro > Opthalmology > Flashcards

Opthalmology Flashcards

1
Q

What is refraction

A

Bending of light when it passes from one optical medium to another

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2
Q

What sturtures in the eye are refractive media

A

Cornea, Aqueous Humor, Lens, Vitruous Humor
All transparent

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3
Q

What Part of the Eye has the highest refractive index

A

Cornea is the most powerful ‘bender’ of light (45D)

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4
Q

What is special about the lens when refracting light

A

It has the power to change its refractive index ‘bending power’ (15D)
due to suspensary ligaments (zonules) which attach the lens to the ciliary body.

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5
Q

What type of rays reach the eye from objects

A

only parallel rays reach the eye for objects over 6m away

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6
Q

What happens to rays from up close objects

A

diverging rays from object can reach the eye
They will be required to bent more to reach the retina: lens will need to have a greater lens power
->lens changes shape (becomes thicker) ->increased power

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7
Q

what is accomodation of the eye?

A

The ability to change focus from distant (infinity) to close objects (20cm)

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8
Q

what occurs to allow accomadation to occur

A

Lens changes shape
Pupils constricts
Eyes converge

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9
Q

What are the main stages involved in Lens Thickening

A

Ciliary muscle contracts (ciliary body buldges, decreasing space between them)
Suspensory ligaments become lax (lens no longer undertension)
Lens becomes thicker

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10
Q

How are ciliary bodies innervated?

A

parasympathetic innervation: causing lens to become thicker/more spherical.

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11
Q

Thick lens properties

A

More powerful, can focus close objects.

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12
Q

What muscle is involved in pupil constriction and how is it innervated

A

Pupillary contrictor (sphincter pupillae)
Concentric muscle
Parasympathetic innervation.

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13
Q

Why does the pupil constrict to focus on close objects

A

To reduce the amount of rays passing through
which will sharpen focus.

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14
Q

What muscles are used to converge the eyes, and how are they innervated

A

Medial rectus, oculomotor CNIII, Both sides.
Medial rectus is thicker than lateral recti muscles.

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15
Q

What is myopia

A

Short-sightedness

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16
Q

What does emmetropia mean?

A

You have perfect vision, lens works efficiently to focus images on retina.

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17
Q

How does myotropia present

A

close objects look clear
distant objects appear hazy.

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18
Q

what causes myopia

A

eyeball too long - most common cause
more curved cornea or lens: bending light more and image is formed infront of the retina.

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19
Q

Why are close objects clear in myotopia

A

The increased power of the cornea/lens is now useful and images are formed on the retina without any acomadative power.

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20
Q

Mytopia symptoms

A

Headaches, not being able to see blackboard.
infants: divergent squint
toddlers: loss of intrest in sports, increased intrest in books
teacher may notice child losing intrest.

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21
Q

How is myopia corrected?

A

Bending power needs to be decreased
Biconcave Lenses: diverges light rays, (has - sign in prescription)
glasses, contact lenses, laser eye surgery

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22
Q

what is Hyperopia

A

farsightedness

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23
Q

Hyperopia presentation

A

close objects look hazy
far objects are clear

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24
Q

How do hypermetrope see far away

A

It uses its accomadative power in order to see far away
brings images that were behind the retina onto it.
As it uses accomadative power for far away objects, Lens has no more additional power for close objects.

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25
Q

hyperopia causes

A

Eye ball too short
cornea and lens too flat
Image forms behind the retina. (uses accomadative power for far objects)

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26
Q

Hyeropia symptoms

A

eyestrain after reading/working
convergent squint in children/toddlers. (needs immediate correction to preserve vision and prevent ‘lazy eye’)

27
Q

Hyperopia correction

A

Biconvex glasses (+ on prescription), focuses distant objects and rest accomadtive power
contact lenses
Laser eye surgery

28
Q

What is Astigmatism

A

More than one images are formed
one image could form on retina and others infront/behind.

29
Q

What are the types of refractive errors

A

myopia
hyperopia
astigmatism
Presbyopia

30
Q

Astigmatism Presentation

A

Both Close and distant images are Hazy at all times.

31
Q

What causes astigmatism

A

Cornea surface has different curvatures in different meridians. (bending of light rays will be different in the axis’s)
(rugby has different meridians, whereas football has all equal meridians)

32
Q

How is astigmatism corrected

A

Special glasses: cylindrical glasses (curved in only one axis) (precription: power +/- and degree of meridian)
Laser eye surgery
Special contact lenses: toric lenses

33
Q

what is Presbyopia?

A

Longsightedness of old age
Lens gets less mobile/elastic (not as capable of changing shape as before)
will require require glasses to read i.e. newspaper
starts in 5th decade (corrected with biconvex lenses)

34
Q

What is phototransduction?

A

conversion of light waves to an electrochemical response by the photoreceptors

35
Q

what happens to light waves after being converted by photoreceptors

A

Rods and cones activate optic nerve cells (generates action potential)

36
Q

What are Rods and cones

A

Modified neurons
made up of axon, synpatic terminal and outersegement containing stack of discs/lamellae ->have photoreceptors

37
Q

What type of light are cones activated by

A

activated by green, blue and red light, and allows you to visualize colour

38
Q

What are the function of rods

A

Allows you to see in dim or reduced light situations

39
Q

What makes up the Lamellae

A

Made up of cell membrane with visual pigaments intergrated into it.
Rhodopsin in rods
Opsins S, M, L in cones

40
Q

How is the visual pigment rhodopsin formed?

A

Rhodopsin formed from Dietary vitamin A (11-cis Retinal) + opsin.

Vitamin A is a chromophore nesting in opsin.

41
Q

What happens when light falls onto Vitamin A

A

Vitamin A= 11-cis retinal
when light falls onto 11-cis retinal it isomeries to all-trans retinal

42
Q

What happens to all-trans retinal

A

All-trans retinal cannot fit into the opsin
rhodopsin splits
resulting in bleaching of the visual purple.

43
Q

How is the phototransduction cascade activated?
and what is the end product?

A

The Rhodospin splits forming all-trans retinal and activated rhodopsin.
The activated rhodopsin then proceeds to activate the rest of the cascade
The phototransduction cascade results in the Na+ channel closing –> hyperpolarisation –> stimulates retinal cell. (AP)

44
Q

How is Rhodopsin (visual pigment) regenerated after spliting

A

All-trans retinal –> all-trans retinol (alcohol/aldehyde) (diffuses out of photoreceptor cell)
All-trans retinol caputured by pigment epithelial cells
In pigment epithelial cell all-trans retinol–>11-cis retinol–>11-cis retinal
11-cis retinal then enters the photoreceptor cell.

45
Q

What can happen to 11-cis retinol/al and all-trans retinol in the pigment epithelial cell

A

It can be converted into retinyl ester, which is unsuable and is degraded and lost from body

46
Q

Where is vitamin A accquired and stored

A

accquired: Diet
stored: Liver.

47
Q

What can you develop after prolonged vitamin A deficiency

A

night blindness
Rods suffer first as there are more and they get bleached and cant reform

48
Q

what is vitamin A required for

A

Required for Epithelium, visual pigments and conjuctiva
corneal epithelium and conjuctiva also affected in deficiency

49
Q

what can cause vitamin A deficiency

A

malnutrition, malabsorption syndromes (coeliac disease,sprue)

50
Q

Vitamin A deficiency signs + symptoms

A

Bitot’s spots (dry appearing trigangular patches on each side of cornea)
Corneal ulceration
corneal melting: this heals by fibrosis leading to opacities

51
Q

What is the visual field.

A

Everything you see with one eye (including periphery)

52
Q

How do objects in field of vision appear on the retina

A

They are upside down and inverted

53
Q

What is the visual Pathway?

A

Optic nerve (passes through optic canal)
Optic Chiasma
Optic tract (synapses at the lateral geniculate body, LGB)
Optic radiation
primary visual cortex

54
Q

Where does the optic radiation pass?

A

It passes behind the internal capsule (via retro-lentiform fibres)
reaches primary visual cortex in occipital lobe

55
Q

Where does the optic tract go

A

It goes to the Lateral geniculate body, in the Thalamus (back of)
and synapses there to form the optic radiation.

56
Q

What occurs at the optic chiasma

A

All the fibres from the same side of the visual field go to the ipsilateral side of the brain. (fibres may stay on the same side.
The optic Chiasma is located above the pituatory fossa.
Temporal fibres don’t cross, Nasal fibres do cross

57
Q

What do each side of the primary visual cortex recieve? and where is it?

A

The primary occipital cortex is located at the back of the occipital lobe and found in the medial surface of the occipital lobe. The primary cortex is found in Area 17.
the primary visual cortex recieves fibres for the ipsilateral half of the visual field

Right visual cortex recieves the left half of the visual field.

58
Q

difference between optic nerve and optic tract

A

optic nerve: carries a right and left half of the visual field (temporal or nasal retina)
optic tract: carries two of the same side of visual field

59
Q

How can R and L visual fields also be refered

A

Temporal or nasal retina

60
Q

What is it called when half blindness occurs in an eye

A

Hemianopia

61
Q

How do visual fields and nerve fibres differ

A

temporal visual fields are the outer half: but become the nasal fibre
nasal visual fields become the temporal fibres

If nasal fibres damaged: loss of temporal vision
if temporal fibres damaged: loss of nasal vision

62
Q

What is it called when the optic chiasma damaged

A

bitemporal hemianopia

63
Q

What occurs when the optic tract is damaged

A

contralateral Homonymous hemianopia

64
Q

What is it called when theres a lesion in the optic radiation

A

contralateral homonymous hemianopia

Year 2 Neuro (14 decks)

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