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My Ophthalmology > Physiology > Flashcards

Physiology Flashcards

1
Q

What are the features of CSF?

A
  • clear, colourless and mostly water
  • made by the secretory epithelium of the choroid plexus
  • formed in the ventricles, circulates in the subarachnoid space and then into the venous circulation
  • supplies water, amino acids and ions
  • removes metabolites
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2
Q

What are the main functions of the CSF?

A
  • Mechanical protection: absorbs shock
  • Homeostatic function: pH affects pulmonary ventilation and cerebral blood flow
  • Circulation: exchange of nutrients and waste
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3
Q

What secretes CSF?

A

the choroid cells which are in many choroid plexuses (the Blood-CSF-Barrier or BCSFB is used)

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4
Q

What is involved in the secretion of CSF?

A

transport of ions across the epithelium from blood to CSF

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5
Q

What is the difference in components of CSF compared to blood plasma?

A
  • lower K, glucose and much lower protein than blood plasma

- higher Na and Cl

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6
Q

What is hydrocephalus?

A

accumulation of CSF fluid causing enlargement of one or more ventricles and an increase in CSF pressure

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7
Q

What are the features of papilloedema?

A
  • excessive CSF production
  • optic disc swelling
  • enlarged blind spot, blurring of vision, visual obscurations and loss of vision
  • flow of CSF pushes on the eye at the back/the optic nerve
  • this can be seen with an ophthalmoscope
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8
Q

What is involves in aqueous humour production?

A
  • contains bicarbonate to buffer H+ produced in anaerobic glycolysis
  • ciliary body produces aqueous humour, it flows into anterior chamber, then drains into scleral venous sinus
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9
Q

What is the pathway for things being seen?

A
  • pattern of the object must fall on the vision receptors
  • accommodation
  • correct amount of light needs to enter the eye
  • energy from the waves of photons must be transduced into electrical signals
  • brain must receive and interpret the signals
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10
Q

What is the order of cells to go through for light?

A

ganglion cells –> bipolar cells –> photoreceptors

the direction of the signal is opposite

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11
Q

What do photoreceptor cells do?

A

convert electromagnetic radiation to neural signals by transduction

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12
Q

What is happening in the neurones when there is no light?

A
  • neurone is depolarised
  • cGMP-gated Na+ channel is open
  • permeability to Na+ and K+ is equal
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13
Q

What happens in the neurones when light hits them?

A
  • it becomes hyperpolarised

- permeability to K+ is increased

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14
Q

What is the pigment in rod cells?

A

rhodopsin

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15
Q

What happens when rhodopsin is stimulated by light?

A
  • activation of G protein called transducin
  • activated cGMP phosphodiesterase so cGMP –> GMP
  • Na+ channels are closed
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16
Q

What is visual acuity?

A

the ability to distinguish two nearby points

this is determined by photoreceptor spacing

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17
Q

What light levels are rods and cones used in?

A 
rods= dim light
cones= normal light
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18
Q

Where are the rods and cones situated?

A
  • cones at fovea
  • rods more general
  • more rods overall than cones
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19
Q

What is the sensitivity of rods?

A
  • high because there are many rods to one ganglion
  • ganglion is triggered even in low light
  • low acuity therefore
20
Q

How are different colours seen?

A

each cone has a different wave that it sees and so a different colour

21
Q

How is a wandering eye in a child treated?

A

covering one of the child’s eyes to stop it developing to amblyopia/lay eye which is cortical blindness

22
Q

What are the main adaptions of the innate immune system for the eye?

A
  • Blink reflex
  • Physical and chemical properties of eye surface
  • Limit exposure/size
23
Q

What are the features of the blink reflex?

A
  • tears flush when blinking to remove pathogens

- anti-adhesive layer doesn’t allow pathogens to stick to the eye

24
Q

What are the features of the chemical properties of the eye surface?

A
  • tears have many elements that are antimicrobial, antiadhesive etc
  • immune cells include neutrophils, macrophages and mast cells
25
Q

What is the main adaptation of the adaptive immune system of the eye?

A
  • Langerhans cells: principle APC for the external eye, have many MHC Class 2 molecules, lots at the corneo-scleral limbus
26
Q

What are the immunological adaptations and components of the conjunctiva?

A
  • Only part of the eye with lymphatic drainage
  • Specialised endothelial venules for migration of lymphoid cells
  • Dendritic cells as APC
  • MALT with immune cells
  • Commensal bacteria
27
Q

What are the immunological adaptations and components of the cornea and sclera?

A
  • Downregulated immune environment

- No lymphatics, no APCs, avascular

28
Q

What are the immunological adaptations and components of the lacrimal gland and its drainage system?

A
  • More plasma cells (IgA) and CD8+ T cells

- MALT tissue in the drainage system

29
Q

What are the immunological adaptations and components of the vitreous, choroid and retina?

A
  • Blood-ocular barrier
  • Lack of APCs
  • Downregulated immune environment
30
Q

What is immune privilege?

A

the eye can tolerate introduction of antigens but there is no inflammatory response

31
Q

What are the specific sites for immune privilege in the eye?

A
  • cornea
  • anterior chamber
  • lens
  • vitreous cavity
  • subretinal space
32
Q

What are the main three mechanisms of immune privilege in the eye?

A
  • Blood tissue barrier and lack of direct lymphatic drainage
  • Environment is rich in immunosuppressive molecules
  • Anterior chamber-associated immune deviation: there is peripheral tolerance to ocular antigens, active downregulation of immune response within the eye
33
Q

What are the features of type 1 hypersensitivity of the eye?

A
  • mast cells express receptors for Fc region of IgE antibody on surface
  • reencounter with antibodies cause histamine and tryptase release
    eg acute allergic conjunctivitis (eye has jelly-like appearance, chemosis is oedema of the conjunctiva)
34
Q

What are the features of type 2 hypersensitivity of the eye?

A
  • cells killed by either complement or NK/macrophages

eg ocular cicatricial pemphigoid (mucous membrane pemphigoid with blistering lesions and scarring), treat with steroids

35
Q

What is an example of type 3 hypersensitivity of the eye?

A

eg autoimmune corneal melting

36
Q

What is an example of type 4 hypersensitivity of the eye?

A

eg corneal graft rejection

37
Q

What are the ocular side-effect of steroids?

A

cataracts and steroid-induced glaucoma

38
Q

What are the three features to look for in an optic disc?

A
  • contour: clear and well defined
  • colour: orange-pink donut with a pale centre
  • cup: normal cup to disc ratio is about 0.3 in an average eye
39
Q

What are the reasons for a pathological pale disc?

A
  • glaucoma
  • optic neuritis
  • arteritic or non-arteritic ischaemic optic neuropathy
  • compressive lesion
40
Q

What are the reasons for a change in the contour of the disc?

A

papilloedema from raised ICP or optic disc drusen which blurs the margins

41
Q

What is the size of an average optic disc?

A

1.5mm

42
Q

What is the difference in neuroretinal rim width?

A

ISNT Rule

- Inferior, superior, nasal, temporal this is the order in which the neuroretinal rim decreases in width

43
Q

What is homonymous hemianopia caused by?

A

one side of the vision is missing on both sides which is caused by a lesion on one side after the chiasm

44
Q

What is OCT and what is it used for?

A
  • Ocular coherence tomography

- depth of macula and is used for looking at wet macular degeneration

45
Q

What is blood in the anterior chamber called?

A

hyphaema

46
Q

What is normal IOP?

A

10-21mmHg

My Ophthalmology (5 decks)

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