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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
Where are the 3 layers of the tear film produced?
Superficial oily layer: Meibomian glands Aqueous tear film: Tear gland Mucinous layer: goblet cells of conjunctiva
26
What are the roles of each of the 3 layers of the tear film?
Superficial Oily Layer: Reduces tear film evaporation Aqueous Tear Film: Oxygen + nutrients + Bactericide Mucinous Layer: Ensures that tear film sticks to the eye
27
Where is the lacrimal gland located?
Superio-laterally to the orbit
28
What are the 3 types of tears?
Basal Tears: produced constantly in absence of irritation Reflex Tears: increased tear production in response to irritation Emotional Tears: crying
29
Describe the innervation of the cornea.
Cornea is very sensitive | Innervated by the ophthalmic branch of the trigeminal nerve (CN V)
30
Describe the drainage of tears.
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
31
What 2 things regulate how much light reaches the retina?
Pupil | Pigmented Uvea
32
What is the term given to perfect focusing ability?
Emmetropia
33
What is the technical term for long-sightedness?
Hyperopia
34
What causes long-sightedness and how can it be corrected?
Parallel rays converge at a focal point posterior to retina Excessively short eyeballs Flat corneal surface (insufficient refractive power) Convex lenses
35
What is the technical term for short-sightedness?
Myopia
36
What causes short-sightedness and how can it be corrected?
Parallel rays converge at a focal point anterior to retina Excessively long eyeball Highly curved cornea (excessive refractive power) Concave lenses
37
What is astigmatism?
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
Which nerve is responsible for accommodation?
Oculomotor Nerve (CN III)
39
What is the near response triad?
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
What is the term given to naturally occurring loss of accommodation with age? How is it treated?
Presbyopia | Convex lenses in near vision
41
Describe the process of accommodation
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
Describe the difference in perfusion between the outer and inner parts of the retina.
Inner 2/3 of the retina = retinal arteries | Outer 1/3 of the retina = choroidal vasculature
43
What part of the retina is responsible for central vision? What does this encompass? How is it assessed?
Fovea (highest concentration of cones) Detail day vision, colour vision Reading, facial recognition Assessed by visual acuity assessment
44
What is peripheral vision responsible for? How is it assessed?
Shape, movement, night vision Navigation vision Assessed by visual field assessment
45
Describe the structure of the retina.
Just inside the choroid = retinal pigment epithelium Outer Layer: photoreceptors (rods + cones) Middle Layer: bipolar cells Inner Layer: retinal ganglion cells
46
What is the function of each layer of the the retina?
Photoreceptors: Detect light Bipolar cells: Local signal processing to improve contrast sensitivity Ganglion cells: Transmission from eye to brain
47
Describe how the fovea appears on a cross-section of the macula.
Appears as a foveal pit due to the absence of overlying retinal ganglion cells
48
State the 2 classes of photo-receptor and their properties.
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
Describe the recycling of photopigments.
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
What are other terms for night vision + day-time vision?
Night: Scotopic (rod) vision Day: Photopic (cone) vision
51
Describe the distribution of rods and cones across the retina.
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
What does a hill of vision represent?
Sensitivity of vision over a visual field
53
Where is the physiological blind spot located?
20 degrees temporal to central vision
54
What are the 3 types of cone photopigment and which colours do they respond maximally to?
S-cone: short wavelength – BLUE M-cone: medium wavelength – GREEN L-cone: long wavelength – RED
55
What is the most common colour vision deficiency and what is it caused by?
Deuteranomaly | Caused by the shifting of the M-cone towards the L-cone
56
What is ametropia?
Mismatch between axial length + refractive power | Parallel light waves don't fall on the retina (no accommodation)
57
What test is used to diagnose colour blindness?
Ishihara Test
58
Describe how light sensitivity changes in dark adaptation.
``` Light sensitivity increases in dark adaptation Biphasic process (cones adapt in 7 mins, rods adapt in 30 mins) ```
59
How does retinal light change in light adaptation and what is responsible for this effect?
Light sensitivity decrease Suppression caused by photopigment bleaching + neuro-adaptation inhibiting rod + cone function Constriction of pupil
60
What is the name of the part of the eye that is black, coloured or white?
Black: Pupil Coloured: Iris White: Sclera
61
What are the corners of the eye called?
Lateral canthus | Medial canthus
62
What is the border between the cornea + sclera called?
Limbus
63
Describe the structure of the conjunctiva
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
Describe the water content in the Sclera + Cornea
Sclera: High water content Cornea: Low water content
65
What is the choroid composed of?
Layers of blood vessels that nourish the back of the eye
66
What enables the eye to perform accommodation?
Elasticity of the lens
67
What is the lens suspended by?
Lens Zonules: fibrous ring consisting of passive connective tissue
68
What is the function of the retina?
Capture light rays that enter the eye | These light impulses are sent to the brain for processing via the optic nerve
69
What is the visible part of the optic nerve called?
Optic disc
70
What is the macula? Where is it located? What is at its centre?
Small, highly sensitive part in centre of retina responsible for detailed central vision Fovea is the centre
71
How do you distinguish between veins and arteries in the eye?
Veins are thicker + darker | Arteries are thinner + lighter
72
What is the blind spot? What is seen here?
Where the optic nerve meets the retina, there are no light sensitive cells Brain fills blindspot with whatever surrounds it
73
Describe the concentration of rods and cones on the fovea
Highest conc. of cones | Low conc. of rods
74
What happens when light passes from one medium into another?
Refraction- velocity + direction change
75
What are the 2 basic types of lenses?
Convex: Converging, takes light rays + brings them to a point Concave: Diverging, takes ligt rays + spreads them out
76
What is Amblyopia?
Uncorrected hyperopia | "Lazy eye"
77
How is astigmatism treated?
Cylinder lenses with/without spherical lenses | Surgery

YR2: Neuroscience and Mental Health (20 decks)

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