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ophthalmology > physiology > Flashcards

physiology Flashcards

1
Q

what is ICP

A

pressure within the cranial cavity

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2
Q

pathophysiology of raised ICP

A

increased pressure in fluid surrounding the brain or an increase in the pressure within the brain itself

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3
Q

name some causes of raised ICP

A

brain tumours
head injuries
hydrocephalus
meningitis
stroke

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4
Q

main complication of raised ICP

A

can cause damage to the brain or spinal chord by compressing them

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5
Q

what makes infants less affected by raised ICP

A

fontanelles and open suture lines means that they have potential for change in cranial size

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6
Q

what is the monro-kellie hypothesis

A

blood, brain and CSF are in equilibrium
if volume of one of the components increases, the volume of a different component must decrease to maintain equilibrium

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7
Q

what happens in brain herniation

A

the brain becomes displaced

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8
Q

name some visual problems caused by raised ICP

A

double vision, blurred vision, loss of vision, pupillary changes, papilledema

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9
Q

describe the optic nerves

A

CNS tracts - paired anterior extensions of the forebrain

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10
Q

what are optic nerves formed by

A

the axons of the retinal ganglion cells

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11
Q

complication of raised ICP on the optic nerve

A

compression of the nerve, as well as the central artery and vein of the retina causes papilledema

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12
Q

name 5 possible visual symptoms of papilledema

A
  • Transient visual obscurations (greying-out of vision)
  • Transient flickering
  • Blurring of vision
  • Constriction of the visual field
  • Decreased colour perception
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13
Q

what are dural septae

A

folds of dura mata creates divisions in the cranial cavity

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14
Q

what is the role of dural septae

A

divide the cranial cavity into falx cerebri and tentorium cerebelli

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15
Q

impact of raised ICP on the dural septae

A

brain can herniate through openings (tentorial notch, foramen magnum)

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16
Q

when will raised ICP affect the oculomotor nerve

A

if medial temporal lobe herniates through tentorial notch

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17
Q

result of raised ICP on the oculomotor nerve (2)

A
  • paralysis of somatic motor innervation - 4 extra-ocular muscles and eyelid
  • paralysis of parasympathetic innervation of sphincter of pupil
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18
Q

clinical sign of damage to the oculomotor nerve due to raised ICP

A

lose/slowness of pupillary light reflex, dilated pupil, ptosis, eye turned inferolaterally (‘down and out’)

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19
Q

why is the trochlear nerve susceptible to damage

A

small diameter with a long intracranial course

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20
Q

result of damage to the trochlear nerve due to raised ICP

A

paralysis of superior oblique muscles

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21
Q

clinical presentation of damage to the trochlear nerve due to raised ICP

A

eye cannot move inferiomedially, resulting in diplopia when looking down

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22
Q

result of damage to the abducent nerve due to raised ICP

A

paralysis of lateral rectus muscle

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23
Q

clinical presentation of damage to the abducent nerve due to raised ICP

A

eye cannot move laterally in horizontal plane, resulting in medial deviation of the eye

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24
Q

what creates the blood-ocular barrier

A

endothelium of capillaries in the iris, ciliary body and retina

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25
what creates the blood-aqueous barrier
capillaries of the iris and ciliary body
26
what creates the blood-retinal barrier
non-fenestrated capillaries of the retinal circulation and tight junctions  between retinal epithelial cells
27
what is the aqueous humour
clear fluid that flows through the anterior segment of the eye
28
name some ways we can overcome the blood-ocular barrier when administrating drugs (3)
- alcohol or acetate makes steroid more hydrophobic - phosphate makes it more hydrophilic - various additives may be added to topical eye drops such as viscosity enhancers, permeation enhancers
29
what is CSF
a clear, colourless fluid that surrounds the brain and the spinal cord
30
what is the main component of CSF
water
31
where is the CSF contained
within the subarachnoid space and the central canal of the spinal cord
32
what are the 3 main roles of CSF
mechanical protection homeostatic function circulation
33
role of CSF in mechanical protection
shock-absorbing medium that protects brain tissue; brain 'floats' inside the cranial cavity
34
role of CSF in homeostatic function
pH of CSF affects pulmonary ventilation and cerebral blood flow, transports hormones
35
role of CSF in circulation
medium for minor exchange of nutrients and waste products between blood and brain tissue
36
what produces CSF
secretory epithelium of the choroid plexus
37
where is the choroid plexus located
in the two lateral ventricles, and in the roof of the third and fourth ventricles
38
what is the usual total volume of CSF
150ml
39
what is the choroid plexus
network of capillaries in the walls of the ventricles
40
name the ions involved in CSF secretion (3)
Na+, Cl- and HCO3-
41
state the flow of CSF (4)
- choroid plexus of each lateral ventricle - third ventricle via narrow openings in interventricular foramina (more added) - flows through the aqueduct of the midbrain into 4th ventricle (more added) - enters subarachnoid space + circulates in the central canal of the spinal chord
42
name the 4 main foramina of the ventricles of the brain
- intraventricular Foramina (of Monroe) - cerebral Aqueduct (of Sylvius) - foramen of Magendie - foramina of Luschka
43
what do the Interventricular foramen (Foramen of Monro) connect
the lateral ventricles to third ventricle
44
how many foramina in the lateral ventricles of the brain
3
45
what is another name for the foramen of megendie
median aperture
46
what is another name for the foramina of luschka
lateral apertures
47
how many foramina are found in the 4th ventricle of the brain
3
48
what does the cerebral aqueduct connect
3rd to 4th ventricle
49
what do the foramen of Magendie and Luschka connect
the 4th ventricle to the subarachnoid space
50
how does CSF return to venous blood
through arachnoid granulations into the superior sagittal sinus
51
what is the role of the blood brain barrier
protects the brain from neurotoxins and helps prevent infection from spreading to the brain
52
how do we obtain CSF
via lumbar puncture
53
what does normal CSF look like
clear and colourless, contains little protein, little immunoglobulins and only 1-5 cells/ml
54
what is an epidural haematoma
arterial bleed between skull and dura
55
what is a subdural haematoma
venous bleed between dura and arachnoid
56
what is hydrocephalus
accumulation of CSF in the ventricular system or around the brain causing ventricular enlargement and increased CSF pressure
57
what are the 2 main causes of hydrocephalus
obstruction of drainage or overproduction of CSF
58
what is papilledema
optic disk swelling due to increased intercranial pressure
59
how do we recognise raised intercranial pressure
transmitted to the subarachnoid space surrounding the optic nerve
60
name the 3 main roles of the aqueous humour
- provides oxygen and metabolites and contains bicarbonate - bicarbonate buffers the H+ produced by the cornea and lens by anaerobic glycolysis - very high in ascorbate, which is a powerful antioxidant
61
where is the aqueous humour produced
in the epithelial later of the ciliary body
62
describe the flow of the aqueous humour in the eye (2)
- from the ciliary body into the posterior chamber - through the pupil into the anterior chamber
63
drainage of aqueous humour
- drains to the scleral venous sinus through a trabecular meshwork and the canal of Schlemm - a small amount diffuses through the vitreous being absorbed across the retinal pigment epithelium
64
where is the canal of schlemm located
in the angle between the iris and cornea (iridocorneal angle)
65
what lines the ciliary body and the posterior surface of the iris
a forward continuation of the pigment epithelium of the retina (PE) overlain by an inner nonpigmented epithelial (NPE) layer
66
what drug can be used to reduce the production of aqueous humour
carbonic anhydrase inhibitors
67
name 2 carbonic anhydrase inhibitors and how they're administered
dorzolamide (eye drops) acetazolamide (oral)
68
name innate immune system components of the eye (3)
blink reflex mucous layer tears
69
role of the blink reflex in protecting the eye
tears flush the surface of the eye
70
how do tears act as a chemical barrier to protect the eye
antimicrobial agents e.g. lysozymes
71
name the immune cells found in tears (3)
neutrophils, macrophages and conjunctival mast cells
72
name the adaptive immune cell found in the eye
langerhans cells
73
role of langerhans cells in the eye
principle antigen presenting cell for the external eye
74
what is the only part of the eye with lymphatic drainage
conjunctiva
75
what is immune privilege
being able to tolerate the introduction of antigens without eliciting an inflammatory response
76
name some sites of the body that have immune privilege
brain/CNS, testes, placenta, eyes
77
name the 5 areas of the eyes which have immune privilege
cornea anterior chamber lens vitreous cavity subretinal space
78
what is sympathetic ophthalmia
rare, bilateral granulomatous uveitis
79
what is the most common cause of sympathetic ophthalmia
trauma
80
give an example of a type 1 hypersensitivity reaction in the eye
acute allergic conjunctivitis
81
give an example of a type 2 hypersensitivity reaction in the eye
ocular cicatricial pemphigoid
82
give an example of a type 3 hypersensitivity reaction in the eye
autoimmune corneal melting
83
give an example of a type 4 hypersensitivity reaction in the eye
corneal graft rejection
84
how is the retina divided
relative to the fovea into a nasal and temporal hemiretina
85
what is contained in the left optic tract
fibres from the left temporal (lateral) retina, and the right nasal (medial) retina
86
what is contained in the right optic tract
fibres from the right temporal retina, and the left nasal retina
87
upper optic radiation
carries fibres from the superior retinal quadrants through the parietal lobe to reach the visual cortex
88
lower optic radiation
carries fibres from the inferior retinal quadrants through the temporal lobe to reach the visual cortex
89
describe the direct pathway for visual signal transmission
photoreceptors to bipolar cells to ganglion cells axons of ganglion cells merge to form the optic nerve
90
role of horizontal cells in signal processing
receive input from photoreceptors and project to other photoreceptors and bipolar cells
91
role of amacrine cells in signal processing
receive input from bipolar cells and project to ganglion cells, bipolar cells, and other amacrine cells
92
role of photoreceptors
convert electromagnetic radiation to neural signals
93
what are the 2 main types of photoreceptors
rods and cones
94
resting membrane potential of photoreceptors
around 20 mV
95
what is rhodopsin
visual pigment molecule
96
what is visual acuity
the ability to distinguish 2 nearby points
97
name 2 factors that affect visual acuity
photoreceptor spacing and refractive power
98
role of cone receptors
colour receptors
99
role of rod receptors
night vision and seeing in black and white

ophthalmology (10 decks)

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