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BRS YEAR 2 > Visual System > Flashcards

Visual System Flashcards

1
Q

Name for the white of the eye

A

Sclera
Has high water content

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2
Q

name for the corner of the eye where eyelids meet?

A

lateral/medial canthus

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3
Q

name for the pink bit in the medial corner?

A

Caruncle

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4
Q

three layers of the eye in order?

A

sclera (hard and opaque) → choroid (pigmented and vascular) → retina (neurosensory tissue)

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5
Q

name for eyeball vascular coat?

A

Uvea

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6
Q

What is the uvea made of

A

choroid, ciliary body, iris (all interconnected)

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7
Q

where is the retina?

A

Inner part of eye

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8
Q

Retina function

A

capturing light rays and turning information into optic nerve signalling

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9
Q

visible portion of the optic nerve is called what?

A

Optic disc

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10
Q

what is the macula responsible for?

A

spot in centre of retina lateral to optic disc responsible for detailed central vision.

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11
Q

name for the spot in the centre of the macula?

A

Fovea
Allows appreciation of fine detail and perform tasks that require central vision such as reading

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12
Q

What does the fovea have the highest concentration of

A

Cone photoreceptors

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13
Q

central vision function vs peripheral vision function?

A

central: detailed day vision, colour, reading, facial recognition.

lacking = poor visual acuity

peripheral: shape, movement, night vision

lacking = poor visual field (can need visual aids even if perfect acuity)

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14
Q
  • layers of the retina → what do they contain?
A

outer layer: photoreceptors (rods and cones) = 1st order neurons

middle layer: bipolar cells (local signal processing) = 2nd order neurons

inner layer: retinal ganglion cells (transmit info to brain) = 3rd order neuron

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15
Q

differences between rods and cones?

A

rods more sensitive to light, slow response, more abundant, do night vision (scotopic) 120 million rods

cones less sensitive with faster response, do day light fine vision and colour vision (photopic) 6 million rods

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16
Q

what happens to light when passing from one medium into another?

A

Velocity changes (refraction)

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17
Q

Two types of lens and their function

A

convex converges light rays to a point

concave spreads light rays outwards

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18
Q

emmetropia vs ametropia?

A

emmetropia = adequate correlation bw axial length and refractive power (parallel light rays fall on retina)

ametropia = mismatch bw axial length and refractive power (parallel light rays don’t fall on retina)

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19
Q

Difference types of ametropia

A

Myopia
Hyperopia
Presbyopia

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20
Q

Myopia

A

parallel rays converge at a point anterior to retina

can be axial → more common or refractive (excessive long globe or excessive refractive power)

Blurred distance vision,squinting and headache

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21
Q

Hyperopia

A

parallel rays would converge at a point posterior to retina

excessive short globe (axial, more common) or insufficient refractive power

visual acuity blurred at near, can be more noticeable at times or when tired

eye pain, headache in frontal region, burning in eyes } = asthenopic symptoms

22
Q

Near response triad

A

pupillary miosis (contraction, sphincter pupillae) to increase depth of field,convergence (medial recti) to align both eyes towards a near object, accommodation (circular ciliary muscle) → increase lens refractive power and increases lens thickness

  • naturally occuring loss of accommodation in old age
23
Q

what is presbyopia?

A

Naturally occurring loss of accommodation in old age

24
Q

What is presbyopia corrected by

A

reading glasses that increase refractive power
(Convex lenses)

25
Q

retinal ganglion of the optic nerve reach which landmark next?

A

Optic chiasm
Approx 53% of fibres decussate to contralateral optic tract

26
Q

Which fibres decussate at the optic chiasm

A

those originating from nasal retina (left hand side of left visual field, right hand side of right visual field = temporal visual field)

  • one eye only
27
Q

lesions anterior to optic chiasm affect what?

A

One eye only

28
Q

lesions on optic chiasm cause what?

A

bitemporal hemianopia (temporal visual field fibres from the nasal retina are the ones crossing over)

29
Q

lesions posterior to optic chiasm cause what?

A

homonymous hemianopia (left half of both eyes gone or right half of both eyes)

30
Q

how does homonymous hemianopia with macular sparing occur?

A

homonymous hemianopia often due to stroke
Central vision preserved as visual cortex area representing macula receives dual blood supply from posterior cerebral arteries of both sides (middle cerebral artery and posterior cerebral artery so adequate perfusion remains if one affected)

Damage to the primary visual cortex

31
Q

why is pupil constriction part of the near response triad?

A

Increases depth of field
Decreases glare

32
Q

What nerves constrict and dilate pupils

A

Constriction by the parasympathetic nerve in CN III
Dilation due to sympathetic nerve

33
Q

pupillary reflex pathway afferent fibres come from where?

A

Light enters eye and strikes retina (retinal ganglion cells participate)
Axons c8nverge it form optic nerve
Decussation of fibres at optic chiasm
Pupil specific ganglion cells exit at posterior third of optic tract before entering lateral geniculate nucleus
Synapse at pretectal nucleus (brainstem)
Synapse on edinger westphal nuclei on both sides of the brain

34
Q

afferent pathway synapses where?

A

Edinger-Westphal nuclei on both sides

35
Q

efferent pathway synapses where?

A

Ciliary ganglion

Edinger Westphalia nucleus receives input from pretectal nucleus
Preganglionic parasympathetic fibres travel along oculomotor nerve where they reach cilliary ganglion and synapse
Postganglionic fibres leave and travel via shirt ciliary nerves reaching sphincter pupilae

36
Q

direct vs consensual light reflex?

A

constriction of light-stimulated eye vs constriction of other eye

37
Q

neurological basis of light reflexes

A

afferent pathway of either single eye stimulates efferent pathway of both eyes

38
Q

right afferent defect creates what pupil response to light?

A

right fails to constrict, no consensual reflex by left

right consensual reflex present when left is lit

39
Q

right efferent defect creates what pupil response to light?

A

right fails to constrict, consensual reflex by left present

no right consensual reflex when left is lit

40
Q

what is the swinging torch test used to determine?

A

partial or relative damage to an afferent pathway

41
Q

What happens in swinging torch

A

both pupils constrict when light swings to undamaged side, both paradoxically dilate when swung to damaged side

42
Q

six extraocular muscles are called what?

A

lateral rectus, medial rectus, inferior rectus, superior rectus, superior oblique, inferior oblique

43
Q

What does superior oblique and inferior oblique do

A

SO-down and out (attached high to temporal side)
IO-up and out (attached on nasal side)

44
Q

innervation of the muscles?

A

superior rectus, inferior rectus, medial rectus, inferior oblique, levator palpebrae superioris (lifts eyelid), pupil constriction = III oculomotor

superior oblique = IV trochlesr

lateral rectus = VI (abducens nerve abducts eye)

45
Q

What is the antero posterior diameter of the eye in adults

A

24mm

46
Q

Visual pathway retina neurones

A

First order neurones-rod and cone retinal photoreceptors
Second order neurones-retinal bipolar cells where 53% of fibres cross at the midline
Third order neurones-retinal ganglion cells-optic tract synapse where lateral geninucleate tract terminates. Then they extend their axons to the primary visual cortex via optic radiations (4th order neurons)

47
Q

Optic chiasm

A

53% of ganglion fibres cross at the optic chiasm
Crossed fibres originating from the nasal retina responsible to temporal visual fields
Uncrossed fibres originating from temporal retina are responsible for nasal visual fields Uncrossed

48
Q

Why does Bitemporal hemianopia occur

A

Caused by enlargement of pituitary gland tumour

49
Q

In dark pupil dilation

A

Increased light sensitivity by allowing more light into the eye
Mediated by sympathetic nerve

50
Q

Relative afferent pupillary defect

A

Partial response still present when damaged eye stimulated

51
Q

Superior and inferior rectus

A

Superior attached to eye at 12 o clock and moves eye up
Inferior attached at 6 o clock and moves eye down

BRS YEAR 2 (43 decks)

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