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1B Neurology & Neuroscience > Anatomy Eye, retina and colour vision > Flashcards

Anatomy Eye, retina and colour vision Flashcards

(65 cards)

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1
Q

what is the external anatomy of the eye?

A
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2
Q

what are the different types of tears?

A

basal

reflex

emotional

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3
Q

how are basal teats produced?

A

by lacrimal system at a constant level- even in absence of irritation or stimulation

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4
Q

when are reflex tears produced?

A

increased tear production in response to ocular irritation

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5
Q

what is the lacrimal reflex pathway made up of?

A
  • afferent pathway, CNS, efferent pathway and lacrimal gland
    • Afferent- cornea, innervation = sensory nerve fibres via cranial nerve V1- ophthalmic trigeminal
      • Trigeminal nerve relays signals to CNS
    • Efferent- parasympathetic
    • Neurotransmitter- acetylcholine
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6
Q

what are tears produced by?

A

lacrimal gland

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7
Q

where is the lacrimal gland located?

A

within orbit

latero-superior to globe

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8
Q

where do tears drain?

A

2 puncta, opening on upper and lower medial lid margins

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9
Q

where do puncta drain to?

A
  • Puncta form opening of superior and inferior canaliculi within lower and upper eyelids
  • Both canaliculi converge as single common canaliculus and drain tear into tear sac
  • Tear drained out of tear sac into nasal cavity through tear duct
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10
Q

what is the cornea covered with?

A

tear film- thin layer fluid

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11
Q

what is the function of the tear film?

A
  • Maintains smooth cornea-to-air surface
  • Important for maintaining clear vision and removing surface debris during blinking
  • bactericide
  • Source of oxygen and nutrient supply to anterior segment
    • Cornea has no blood vessels
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12
Q

what are the layers of the tear film?

A

superficial lipid layer

aqueous tear film

mucinous layer

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13
Q

what is the superficial lipid layer?

A
  • Responsible protecting tear film from rapid evaporation
  • Secreted by Meibomian glands situated along eyelid margins
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14
Q

what is the aqueous tear film?

A
  • Main bullk of tear film
  • Delivers oxygen and nutriet to surrounding tissue
  • Contains factors against potentially harmful bacteria
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15
Q

what is the mucinous layer?

A
  • Ensures tear film sticks to eye surface
  • Renders surface eye ‘wettable’
  • Mucin molecules act by binding water molecules to hydrophobic corneal epithelial cell surface
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16
Q

what is the conjunctiva?

A

thin, transparent tissue that covers outer surface of eye

  • Begins at outer edge of cornea, covers visible part of eye and lines inside of eyelids
  • Nourished by tiny blood vessels that are nearly invisible to naked eye
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17
Q

what happens in conjunctivitis to the visible conjunctiva?

A

infection of the conjunctiva

blood vessels become visible to naked eye

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18
Q

what is the anterio-posterior diameter of eye in adults?

A

24mm

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19
Q

where does the eye sit?

A

anatomical space of the oribit

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20
Q

what is the eye enclosed by?

A

bone walls

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21
Q

what is the posterior coat of the eye

A

sclera

choriod

retina

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22
Q

what is the anatomy of the eye in lateral view?

A
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23
Q

what is the sclera responsible for?

A
  1. Sclera- hard and opaque
    1. Protection
    2. Shape maintenance of eye
    3. High water content
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24
Q

what is the choroid responsible for?

A
  1. Choroid- pigmented and vascular
    1. Providing circulation to eye
    2. Shielding out unwanted scattered light
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25
what is the retina responsible for?
1. Retina- neurosensory tissue 1. Converting light into neurological impulses 2. Transmitted to brain via optic nerve
26
what is the cornea?
* Transparent, dome shaped window covering front of eye * Low water content * Refracting surface providing 2/3 eye focusing power * Clear window to look through
27
what are the layers of the cornea?
1. Epithelium 2. Bowman’s membrane 3. Stroma- contributes towards transparency 4. Descement’s membrane 5. Endothelium-pumps fluid out corneal and prevents corneal oedema
28
what is the uvea?
* Vascular coat of eyeball and lies between sclera and retina * 3 parts 1. Iris 2. Ciliary body 3. Choroid
29
what can disease of uvea cause?
connected intimately disease of one part affects other portions but not always to same degree
30
where is the choroid?
between retina and sclera
31
what does the choroid do?
composed of layers of blood vessels that nourish back of eye
32
what does the iris do?
controls light levels inside eye rebound opening in center-pupil embedded with tiny muscles that dilate and constrict pupil size
33
what is the structure of the lens?
* Outer acellular capsule * core of Regular inner elongated cell fibres- transparency
34
what can happen to the lens with age?
loss of transparency- cararacts
35
what are the functions of the lens?
* Transparency * Regular structure * Refractive power * 1/3 eye focusing power- higher refractive index than aqueous fluid and vitreous * Accommodation * Elasticity
36
what is the retina?
* Thin layer of tissue * Lines inner part of eye * Capture light rays that enter eye * Light impulses sent to brain for processing via optic nerve
37
what does the optic nerve do?
transport electrical impulses from retina to brain connects near back of eye near macula visible portion= optic disc
38
what is the blind spot caused by?
where optic disc meets retina= no light cells= blind spot= optic disc
39
where is the macula?
located in centre of retina. temporal to optic nerve
40
what is the macula responsible for?
* Small and highly sensitive * Responsible for detailed coloured vision * Macula allows detail and to perform tasks that require central vision such as reading
41
what is the centre of the macula?
fovea
42
what is the make up of the fovea?
* Highest concentration of cones, low concentration rods * Only fovea has concentration of cones to perceive in detail
43
what is central vision? (macula vision)
* Detail day vision * Colour vision- highest conc cone photoreceptors on fovea * Reading, facial recognitions * Assessed by visual acuity assessment * Loss foveal vision- poor visual acuity
44
what is peripheral vision?
* Shape, movement, night vision * Navigation vision * Assessed by visual field assessment
45
what is the effects of extensive loss visual field?
* = unable navigate in an environment – may need white stick even with perfect acuity
46
what is the structure of the retina?
outlayer- retinal pigment epithelium middle layer- bipolar cells (2nd order neuron) inner layer- neuroretina
47
what is the retinal pigment epithelium?
* Situated in front choroid * Photoreceptors (1st order neuron) * Detection light * Transport nutrient from choroid to photoreceptors and remove metabolic waste from retina
48
what do the bipolar cells do?
Local signal processing to improve contrast sensitivity, regulate sensitivity
49
what does neuroretina do?
* Retinal ganglial cells (3rd order neuron) * Transmission signal from eye to brain
50
what is neuroretina made up of?
photo-receptors and neurons
51
what are the classes of photoreceptors?
rods cones (overall more rods than cones)
52
what are the features of rods?
* Longer outer segment with more photosensitive pigment * More sensitive to light than cones * Main photoreceptors in night vision (scotopic vision) * Slow response to light
53
what are the features of cones?
* Less sensitive to light * Shorter outer segment * Day fine vision and colour vision * Faster response
54
where are photoreceptors synthesised?
* in inner segment and transported to outer segment
55
what is the outer segment made up of?
Stacks of discs
56
what happens to distal discs?
distal discs with deactivated photo-pigments are shedded from tips phagocytosed by retinal epithelial cells
57
what happens to deacitvated photopigments in retinal epithelial cells?
regenerated and transported to photo-receptors
58
what is the distribution of photoreceptors?
* Central eye- highest cone cells (only cone cells in macula for photopic (day vision) * Peripheral= highest rod- highest density outside macula and tail off towards periphery (20-40deg away from fovea) * No photoreceptors in blind spot * Rod cells absent in macula
59
what is the frequency spectrum of rod cells?
only has single peak light sensitivity so not sensitive to any particular colour
60
what is the frequency spectrum of cone cells?
* S-cones- short wavelength sensitivity= blue * M-cones- medium wavelength sensitivity = green * L-cones- long wavelength sensitivity= red * Yellow light has wavelength between M cones and L cones * Stimulates both equally
61
what is the commonest vision deficiency in frequency spectrum?
Deuteranomoly shifting M-cone sensitivity peak towards that of L-cone curve red- green confusion
62
what are the different colour vision deficiencies?
* Deuteranomaly= daltonism and most frequent form colour blindness * Not completely colour blind but don’t perceive colour red due to anomalous trichromatism * Full colour blindness only in very small % population= ACHROMATOPSIA= monochromatism
63
what can achromatopsia be caused by?
* Can be caused by blue cone monochromatism with only presence blue L-cones * Normal day light visual acuity * Can be cause by rod monochromatism * Total absence of all cone photoreceptors * No functional day vision
64
what is the test for colour blindness?
Ishaihara test
65

1B Neurology & Neuroscience (14 decks)

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