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YR2: Neuroscience and Mental Health > Structure and Function of the Eye > Flashcards

Structure and Function of the Eye Flashcards

1
Q

What is the average anterior-posterior diameter of the orbit?

A

24 mm

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2
Q

What are the three layers of the eye? Describe their propertiesand function.

A

Sclera: Hard + opaque, Maintains shape
Choroid: Pigmented + vascular, Provides circulation, Shields out unwanted scattered light
Retina: Neurosensory, Converts light into neurological impulses

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3
Q

What are the 2 segments of the eye separated by?

A

Lens

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4
Q

Which humours are found in the 2 segments of the eye?

A 
Anterior = aqueous humour  
Posterior = vitreous humour
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5
Q

Describe the production and drainage of aqueous humour.

What is the role of aqueous humour?

A

Produced by ciliary body
Drained via trabecular meshwork into canals of Schlemm
Provides nutrients to cornea + other tissues in anterior chamber

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6
Q

Describe vitreous humour.

What is the function of vitreous humour?

A

99% water trapped inside a jelly matrix

Mechanical support for the eye

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7
Q

Describe how the vitreous humour changes with age.

A

Loses its jelly consistency, liquefies + can become detached from the retina
Vitreous detachment in seen as floaters

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8
Q

What are the potentially disastrous consequences of vitreous humour detachment?

A

Detaching from the retina could cause a small tear in the peripheral retina
Allowing liquid vitreous to seep into the sub-retinal space + lead to retinal detachment
If untreated, it can lead to blindness

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9
Q

What are the 2 layers of the iris?

A

Anterior – stromal layer containing muscle fibres

Posterior – epithelium

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10
Q

What is the collective term for the choroid, iris and ciliary body? What is its function? Where is it located?

A

Uvea
Vascular coat of the eye
Lies between sclera + retina

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11
Q

What is the normal range for intraocular pressure?

A

12-21 mm Hg

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12
Q

What is glaucoma?

What changes can be seen in the retina in glaucoma?

A

Condition of sustained raised intraocular pressure
Retinal ganglion cell death
Enlarged optic disc cupping

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13
Q

What are the consequences of untreated glaucoma?

A

Progressive loss of peripheral vision

Blindness

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14
Q

What is the most common type of glaucoma and what is it caused by?

A

Primary open angle glaucoma

Caused by a functional blockage of the trabecular meshwork

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15
Q

State another relatively common type of glaucoma. What is it caused by?

A

Closed angle glaucoma
(acute or chronic)
Caused by the forward displacement of the iris-lens complex –narrowing the trabecular meshwork

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16
Q

In what type of patients does closed angle glaucoma tend to occur and what is the treatment?

A 
Small eyes (hypermetropic) 
Treatment: peripheral laser iridotomy
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17
Q

Describe the structure of the lens.

A

Outer acellular capsule

Regular inner elongated fibres, which give the lens its transparency (may lose transparency with age- cataract)

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18
Q

Which 2 structures provide the majority of the refractive power of the eye?

A 
Cornea = 2/3 
Lens = 1/3
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19
Q

What layer of the eye is the cornea continuous with?

A

Sclera

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20
Q

Other than its role in refracting light, what else is the cornea necessary for?

A

Physical barrier: protects eye from opportunistic infection

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21
Q

What happens if you hydrate the cornea?

A

It goes white

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22
Q

What are the layers of the cornea?

A 
Epithelium 
Bowmans membrane
Stroma 
(Dua's layer)
Descemet's membrane
Endothelium
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23
Q

What is the role of the endothelial layer of the cornea?

A

Pumps out fluid from the stroma + prevents corneal oedema

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24
Q

What are the 4 main roles of tear film?

A

Maintains smooth cornea-air surface
Oxygen supply to cornea
Removes surface debris
Bactericide

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25
Q

Where are the 3 layers of the tear film produced?

A

Superficial oily layer: Meibomian glands
Aqueous tear film: Tear gland
Mucinous layer: goblet cells of conjunctiva

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26
Q

What are the roles of each of the 3 layers of the tear film?

A

Superficial Oily Layer: Reduces tear film evaporation
Aqueous Tear Film: Oxygen + nutrients + Bactericide
Mucinous Layer: Ensures that tear film sticks to the eye

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27
Q

Where is the lacrimal gland located?

A

Superio-laterally to the orbit

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28
Q

What are the 3 types of tears?

A

Basal Tears: produced constantly in absence of irritation
Reflex Tears: increased tear production in response to irritation
Emotional Tears: crying

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29
Q

Describe the innervation of the cornea.

A

Cornea is very sensitive

Innervated by the ophthalmic branch of the trigeminal nerve (CN V)

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30
Q

Describe the drainage of tears.

A

Drain into 2 puncta via 2 tiny holes in the upper + lower medial lid margins
Then drain into superior + inferior canaliculi –> common canaliculus –> tear sac
Tear sac drains through nasolacrimal duct, which opens up in the inferior meatus

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31
Q

What 2 things regulate how much light reaches the retina?

A

Pupil

Pigmented Uvea

32
Q

What is the term given to perfect focusing ability?

A

Emmetropia

33
Q

What is the technical term for long-sightedness?

A

Hyperopia

34
Q

What causes long-sightedness and how can it be corrected?

A

Parallel rays converge at a focal point posterior to retina
Excessively short eyeballs
Flat corneal surface (insufficient refractive power)
Convex lenses

35
Q

What is the technical term for short-sightedness?

A

Myopia

36
Q

What causes short-sightedness and how can it be corrected?

A

Parallel rays converge at a focal point anterior to retina
Excessively long eyeball
Highly curved cornea (excessive refractive power)
Concave lenses

37
Q

What is astigmatism?

A

Parallel rays come to focus in 2 focal lines rather than a single focal point
Cornea is oval rather than round
Refractive power varies in different planes (in some planes hypermetropic, in others myopic)

38
Q

Which nerve is responsible for accommodation?

A

Oculomotor Nerve (CN III)

39
Q

What is the near response triad?

A

Pupillary Miosis (constriction of sphincter pupillae): increases depth of field
Convergence: medial recti of both eyes contract to align both eyes towards a near object
Accommodation: ciliary muscles contract to thicken lens + increase its refractive power

40
Q

What is the term given to naturally occurring loss of accommodation with age? How is it treated?

A

Presbyopia

Convex lenses in near vision

41
Q

Describe the process of accommodation

A

Contraction of circular ciliary muscle
Causes relaxation of zonules
Absence of Zonular tension allows lens to return to natural convex shape due to its innate elasticity

42
Q

Describe the difference in perfusion between the outer and inner parts of the retina.

A

Inner 2/3 of the retina = retinal arteries

Outer 1/3 of the retina = choroidal vasculature

43
Q

What part of the retina is responsible for central vision? What does this encompass? How is it assessed?

A

Fovea (highest concentration of cones)
Detail day vision, colour vision
Reading, facial recognition
Assessed by visual acuity assessment

44
Q

What is peripheral vision responsible for? How is it assessed?

A

Shape, movement, night vision
Navigation vision
Assessed by visual field assessment

45
Q

Describe the structure of the retina.

A

Just inside the choroid = retinal pigment epithelium
Outer Layer: photoreceptors (rods + cones)
Middle Layer: bipolar cells
Inner Layer: retinal ganglion cells

46
Q

What is the function of each layer of the the retina?

A

Photoreceptors: Detect light
Bipolar cells: Local signal processing to improve contrast sensitivity
Ganglion cells: Transmission from eye to brain

47
Q

Describe how the fovea appears on a cross-section of the macula.

A

Appears as a foveal pit due to the absence of overlying retinal ganglion cells

48
Q

State the 2 classes of photo-receptor and their properties.

A

Rods
Longer outer segment with photo-sensitive pigments
100X MORE sensitive to light than cones
SLOW response to light
Responsible for night vision (scotopic)
120 million rods
Cones
LESS sensitive to light
FASTER response to light
Responsible for daylight, fine + colour vision (photopic)
6 million cones

49
Q

Describe the recycling of photopigments.

A

Synthesised in inner photo-receptor segment + transported to the outer segment discs
Distal discs with deactivated photo-pigments are shredded from the tips + phagocytosed by retinal pigment epithelial cells
Deactivated photo-pigments are regenerated inside the retinal pigment epithelial cells + are then transported back to the photo-receptors

50
Q

What are other terms for night vision + day-time vision?

A

Night: Scotopic (rod) vision
Day: Photopic (cone) vision

51
Q

Describe the distribution of rods and cones across the retina.

A

Rods: highest density just outside macula
Decrease in density the further you move away from the macula
NO rods in the macula
Cones are ONLY found in the macula
Highest density of cones is in the fovea

52
Q

What does a hill of vision represent?

A

Sensitivity of vision over a visual field

53
Q

Where is the physiological blind spot located?

A

20 degrees temporal to central vision

54
Q

What are the 3 types of cone photopigment and which colours do they respond maximally to?

A

S-cone: short wavelength – BLUE
M-cone: medium wavelength – GREEN
L-cone: long wavelength – RED

55
Q

What is the most common colour vision deficiency and what is it caused by?

A

Deuteranomaly

Caused by the shifting of the M-cone towards the L-cone

56
Q

What is ametropia?

A

Mismatch between axial length + refractive power

Parallel light waves don’t fall on the retina (no accommodation)

57
Q

What test is used to diagnose colour blindness?

A

Ishihara Test

58
Q

Describe how light sensitivity changes in dark adaptation.

A 
Light sensitivity increases in dark adaptation
Biphasic process (cones adapt in 7 mins, rods adapt in 30 mins)
59
Q

How does retinal light change in light adaptation and what is responsible for this effect?

A

Light sensitivity decrease
Suppression caused by photopigment bleaching + neuro-adaptation inhibiting rod + cone function
Constriction of pupil

60
Q

What is the name of the part of the eye that is black, coloured or white?

A

Black: Pupil
Coloured: Iris
White: Sclera

61
Q

What are the corners of the eye called?

A

Lateral canthus

Medial canthus

62
Q

What is the border between the cornea + sclera called?

A

Limbus

63
Q

Describe the structure of the conjunctiva

A

Thin, transparent tissue covering surface of eye
Begins at outer edge of cornea, covers visible part of eye + lines inside of eyelids
Nourished by tiny blood vessels

64
Q

Describe the water content in the Sclera + Cornea

A

Sclera: High water content
Cornea: Low water content

65
Q

What is the choroid composed of?

A

Layers of blood vessels that nourish the back of the eye

66
Q

What enables the eye to perform accommodation?

A

Elasticity of the lens

67
Q

What is the lens suspended by?

A

Lens Zonules: fibrous ring consisting of passive connective tissue

68
Q

What is the function of the retina?

A

Capture light rays that enter the eye

These light impulses are sent to the brain for processing via the optic nerve

69
Q

What is the visible part of the optic nerve called?

A

Optic disc

70
Q

What is the macula? Where is it located? What is at its centre?

A

Small, highly sensitive part in centre of retina responsible for detailed central vision
Fovea is the centre

71
Q

How do you distinguish between veins and arteries in the eye?

A

Veins are thicker + darker

Arteries are thinner + lighter

72
Q

What is the blind spot? What is seen here?

A

Where the optic nerve meets the retina, there are no light sensitive cells
Brain fills blindspot with whatever surrounds it

73
Q

Describe the concentration of rods and cones on the fovea

A

Highest conc. of cones

Low conc. of rods

74
Q

What happens when light passes from one medium into another?

A

Refraction- velocity + direction change

75
Q

What are the 2 basic types of lenses?

A

Convex: Converging, takes light rays + brings them to a point
Concave: Diverging, takes ligt rays + spreads them out

76
Q

What is Amblyopia?

A

Uncorrected hyperopia

“Lazy eye”

77
Q

How is astigmatism treated?

A

Cylinder lenses with/without spherical lenses

Surgery

YR2: Neuroscience and Mental Health (20 decks)

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