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Y2 - NMH > Structure and Function of the Eye > Flashcards

Structure and Function of the Eye Flashcards

1
Q

Label this diagram of the orbit bone structure

A
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2
Q

Label this diagram of the eye

A
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3
Q

3 types of tears?

A
  • Basal tears
  • Reflex tears - in response to irritation
  • Crying tears
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4
Q

Outline the afferent then efferent pathway in reflex tear production

A
  • Afferent - irritant detected at the cornea - afferent pathway along the opthalmic branch of the trigeminal nerve
  • There is then efferent fibres which are parasympathetic fibres secreting acetylcholine causing reflex tear production
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5
Q

Label this diagram for the production and drainage of tears

A
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6
Q

Describe the pathway (anatomically not neurally) of tear production and drainage

A
  • Lacrimal gland produces tears
  • Then drains into the puncta on the medial lid margins on upper and lower eyelids
  • Then drains through the superior and inferior canaliculi
  • Then into the tear sac
  • Then into the tear duct
  • Then into the nasal cavity
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7
Q

What are the functions of the tear film?

A
  • Maintains smooth cornea-air surface
  • Provides oxygen supply to cornea
  • Debris removal
  • Bactericide
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8
Q

What are the 3 layers of tear film - give the functions of these different layers for all and where they are secreted from where applicable?

A
  1. Superficial oily layer
  • Protects tear film from rapid evaporation
  • Secreted from Meiobomian glands along lid margins
  1. Aqueous tear film
  • Delivers oxygen and nutrients to the surrounding tissue
  • Bactericide
  • Lubricant
  • Produced from lacrimal gland
  1. Mucinous layer
  • Binds water molecules to the hydrophobic corneal epithelial cells
  • Basically ensures tear film ‘sticks’ to the cornea
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9
Q

What are the 3 layers of the coat of the eye (in order from outer to inner) and what are their functions?

A
  1. Sclera - hard and opaque fibrous layer that protects the eye and maintains its shape
  2. Choroid - provide circulation to the eye and shield out unwanted scattered light
  3. Retina - neurosensory tissue that converts light into neurological influences to be transmitted to the optic nerve
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10
Q

The sclera is continuous with the …..

A

The sclera is continuous with the cornea

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11
Q

Compare the water content of the sclera and the cornea

A
  • Sclera - high water content
  • Cornea - low water content
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12
Q

3 functions of the cornea?

A
  1. Refracting surface - provides 2/3 rds of the eye’s focusing power - convex shape
  2. Physical barrier
  3. Infection barrier
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13
Q

What are the 5 layers of the cornea?

A
  1. Epithelium
  2. Bowman’s membrane
  3. Stroma
  4. Descemet’s membrane
  5. Endothelium
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14
Q

What is the function of the endothelial cornea?

A
  • To pump out excess fluid from the cornea - thereby preventing corneal oedema and haziness
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15
Q

What is the uvea and what are the 3 parts of it?

A
  • Vascular coat of the eyeball
  • 3 parts:
  1. Iris
  2. Ciliary body
  3. Choroid
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16
Q

Label this eye

A
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17
Q

What happens if you hydrate the cornea?

A

It becomes opaque to the point it appears white

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18
Q

Describe the structure of the lens

A
  • Outer acellular capsule
  • Inner regular arrangement of elongated cell fibres
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19
Q

What is the function of the lens?

A
  • Provides 1/3 rd of the refractive power of the eye
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20
Q

1) What happens in cataract?
2) What are the different types of cataract?

A

1)

  • Opaque lens

2)

  • Nuclear
  • Cortical
  • Posterior capsular
  • Anterior capsular
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21
Q

1) What are lens zonules including what they consist of?
2) What is the function of these lens zonules?

A

1)

  • Fibrous ring that suspends the lens
  • Passive connective tissue

2)

  • Suspends the lens by attaching to the ciliary body
  • Tension across the lens zonules keeps the lens taut
  • Upon release of the tension in the lens, the innate elasticity of the lens makes it return to its natural more convex shape
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22
Q

Why do you often get shorsightedness with age?

A
  • The lens zonules loses its elastic properties so when the ciliary muscles constricts, the lens remains wide and thin
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23
Q

What is the visible portion of the optic nerve called?

A

The optic disc

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24
Q

1) Where is the macula located?
2) What is the function of the macula and what does it contain?

A

1)

  • Centre of the retina
  • Temporal (lateral) to the optic nerve

2)

  • Highly sensitive part of the retina - aids high detail and central vision tasks such as reading
  • Contains the fovea
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25
Q

Where are the posterior and anterior segments and what separates them?

A
  • Ocular structures anterior to the lens
  • Ocular structures posterior to the lens
  • Lens separates them
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26
Q

What are the 2 anatomical chambers within the eye?

A
  • Anterior chamber
  • Posterior chamber
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27
Q

1) Where is the anterior chamber?
2) What is the function of the anterior chamber?

A

1)

  • Between the cornea and lens

2)

  • Contains aqueous fluid
  • Supplies nutrients
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28
Q

What are the 2 layers of the iris, and what is one of them composed of?

A
  1. Thin posterior pigmented epithelial layer
  2. Thick anterior layer - stromal tissue and smooth muscle
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29
Q

Describe the path along which aqueous humour flows from where its produced, where it fills, then the drainage pathway

A
  • Produced by the ciliary body
  • Fills the anterior chamber
  • Drained by the trabecular meshork futher anteriorly in front of the iris, and also drained by the canals of Schlemm → ultimately into venous system
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30
Q

Where is the trabecular meshwork located?

A

At the junction between the ciliary body and the cornea

31
Q

Where is the canal of Schlemm located?

A

In the cornea

32
Q

What is the first line of treatment in treatment of high intra-ocular pressure?

A

Prostaglandin analogues

33
Q

Describe the pathophysiology of primary open angle glaucoma

A
  • Trabecular Meshwork Dysfunction
  • Therefore impaired aqueous humour drainage
  • This causes increase in intraocular pressure
  • This increased IOP causes damage to the retinal cell ganglion / optic nerve
  • This causes the symptoms of visual field loss
34
Q

Describe the pathophysiology of closed angle glaucoma

A
  • Increased pressure pushes the iris / lens complex forward, blocking the trabecular meshwork
  • Thus preventing the drainage of aqueous humour
  • Thus increasing the intraocular pressure even further
  • This causes damage to the retinal ganglion cells / optic nerve
  • This causes the symptoms of visual field loss
35
Q

What are the risk factors for closed angle glaucoma?

A
  • Hypermetropia (long-sightedness) - short eyes
  • Narrow angle at trabecular meshwork
36
Q

How is closed angle glaucoma treated?

A
  • Peripheral laser irodotomy to create a drainage hole in the iris for aqueous humour
37
Q

What can you see in the fundoscopy of the eye in glaucoma and explain what causes this finding?

A
  • Enlarged optic disc cupping
  • Due to loss of ganglion nerve fibres causing hollowing out of the optic nerve head
38
Q

What is the optic nerve blind spot and what is the corresponding anatomical landmark for it?

A
  • Where the optic nerve meets the retina, there are no light-sensitive cells - this is the physiological blind spot
  • The corresponding anatomical blind spot is the optic disc
39
Q

Does the fovea contain a high or low amount of cones and rod cells?

A
  • Highest conc of cones
  • Low conc rods
40
Q

There is a 1:1 ratio between ….. and ….. ….. in the fovea

A

There is a 1:1 ratio between photoreceptors and ganglion cells in the fovea

41
Q

1) What types of vision is central (macular) vision useful in , and how does the macula enable this functionally?
2) How to assess central vision?

A

1)

  • PHOTOPIC VISION
  • Detailed vision high visual acuity - due to small receptive field - 1:1 photoreceptor : ganglion cell in fovea / macula
  • Colour vision - due to high concentration of cone cells (detect colour) in fovea / macula

2)

  • Visual acuity assessment - poor visual acuity in loss of foveal vision
42
Q

Label this diagram of cells in the eye from the sclera to the optic nerve

I blocked out 2 intermediate type cells but just ignore these don’t need to learn them

A
43
Q

Describe the retinal structure - layers of the retina and the cells involved

A
  • Outer layer - retinal pigment epithelium, photoreceptors (cones and rods) - first order neurones
  • Middle layer - bipolar cells, intermediate neurones - second order neurones
  • Inner layer - retinal ganglion cells - third order neurones
44
Q

What is the function of the retinal pigment epithelium?

A
  • Transport nutrients from the choroid to the photoreceptors (rods and cones)
  • Remove metabolic waste from the uvea
45
Q

What cells constitute the neuroretina?

A
  • Photoreceptors - rods and cones
  • Intermediate neurones including bipolar neurones
  • Inner layer of retinal ganglion cells
  • Through to optic nerve fibres
46
Q

Give some functions of second order neurones - bipolar neurones

A
  • Improve contrast sensitivity
  • Regulate sensitivity
47
Q

What is the macula lutea?

A

Pigmented (yellow) region at the centre of the retina at the macula

48
Q

Why is there a foveal pit in the centre of the macula?

A
  • Due to absence of overlying ganglion layer
49
Q

How can you assess the health of the fovea, or of the retina in general using imaging?

A
  • Optical coherence tomography scan - to see the thickness of the various retinal layers
50
Q

Compare the rod and cone photoreceptor properties - in terms of light sensitivity and visual acuity, as well as what type of vision they are useful for

A

Rods

  • Much more light-sensitive - due to large receptive fields downstream
  • Low visual acuity - due to large receptive fields downstream
  • Scotopic vision - peripheral vision, night vision

Cones

  • Less sensitive to light - due to small receptive fields downstream
  • High visual fields - due to small receptive fields downstream
  • Photopic vision - day light fine vision, colour vision
51
Q

What is scotopic vision, and what cells enable it?

A
  • Peripheral vision
  • Night vision
  • Rod cells enable it
52
Q

What is photopic vision and what cells enable it?

A
  • Detailed day light vision
  • Colour vision
  • Cone cells enable it
53
Q

Describe how cone cells enable colour vision by the frequency spectrum - the 3 types of cone cells

A
  • 3 type of cone cells with different peak wavelength sensitivities:
  1. S-cone cells: small wavelength photosensitive pigment - blue detection
  2. M-cone cells: medium wavelength photosensitive pigment - green detection
  3. L-cone cells: large wavelength photosensitive pigment - red detection
  • To experience yellow light, both M- and L-cone cells are stimulated mixture of red and green
54
Q

What is the name of the most common form of colour blindness and what occurs in it?

A
  • Deuteranomaly
  • M-cone sensitivity peak shifts to that of L-cone sensitivity curves
  • Thus red-green confusion
55
Q

1) What does anomalous trichromatism mean?
2) What is the most common form of anomalous trichromatism?

A

1)

  • Shift in the photo-pigment sensitivity

2)

  • Deuteranomaly
56
Q

Dichromatism is a form of anomalous trichromatism, what happens in dichromatism?

A
  • 2 cone photoreceptors types are present only (2 types of photosensitive cones - different photosensitive pigments)
57
Q

Monochromatism is a form of anomalous trichromatism, what happens in monochromatism?

A

Complete absence of colour vision

58
Q

What test is there for red-green colour blindness?

A
  • Ishihara test
  • That numbers in the circle thing
59
Q

Describe light-dark adaptation of rods and cones

A

Dark adaptation

  • Biphasic process
  • Retina increases its light sensitivity
  • Retina switches from photopic to scotopic vision
  • Regeneration of rhodopsin in rods

Light adaptation

  • Bleaching of pigments mediates the process
  • Inhibition of both rod / cone function
  • Pupillary constriction
60
Q

Describe the path that light photons have to pass through to reach the retina eventually - in terms of the different mediums it has to pass, and it refracts at each time

A
  1. Tear film
  2. Cornea
  3. Aqueous humour
  4. Lens
  5. Vitreous humour
  6. Retina
61
Q

How to calculate the refractive index of a particular medium?

A
  • n = Speed of light in a vacuum / speed of light in the medium
62
Q

The ….. a convex lens is, the closer the focal point is to the lens

A

The thicker a convex lens is, the closer the focal point is to the lens

63
Q

1) Define emmetropia and ametropia, and what happens to cause both of them?
2) What are the 4 types of ametropia?

A

1)

Emmetropia - refractive power = 0

  • Appropriate correlation between axial length and refractive power
  • Such that parallel light rays fall on the retina (no accomodation)
  • And no visual correction is necessary

Ametropia - refractive error

  • Mismatch between axial length and refractive power
  • Such that parallel light rays do not fall on the retina (no accomodation)
  • And visual correction is necessary

2)

  1. Myopia (nearsightedness)
  2. Hyperopia (farsightedness)
  3. Astigmatism
  4. Presbyopia
64
Q

1) What essentialy happens in hyperopia?
2) What are the 2 types (causes) of hyperopia?

A

1)

  • Parallel rays converge at a focal point posterior to the retina

2)

  • Axial hyperopia - globe too short
  • Refractive hyperopia - insufficient refractive power of lens
65
Q

1) What essentialy happens in myopia?
2) What are the 2 types (causes) of myopia?

A

1)

  • Parallel rays converge at a focal point anterior to the retina
  • Near-sightedness

2)

  1. Axial myopia - due to globe being too long
  2. Refractive myopia - excess refractive power of lens
66
Q

What is amblyopia?

A
  • Uncorrected hyperopia where >5D
  • This causes the brain to essentially ignore the sensory input from this eye - lazy eye
67
Q

How do corrective lenses correct vision in myopia and in hyperopia?

A
  • Myopia - concave lenses cause divergence of light rays to correct the focal point which is initially anterior to the retina in myopia such that it hits the retina
  • Hyperopia - convex lenses cause convergens of light rays to correct the focal point which is initially posterior to the retina in myopia such that it hits the retina - increases the refractive power
68
Q

What is the pathophysiolgy of astigmatism?

A
  • Refractive media is elliptical not spherical
  • So light coming into the eye hits the lens, and is refracted in different ways (light refracts differently along one meridian than along meridian perpendicular), so there are two focal planes. You have a focal area between these two focal points
69
Q

How is astigmatism corrected using corrective lenses?

A
  • Using cylinder lenses
  • Light travels through the vertical part of the cylinder and is not bent. Light passing perpendicular to the cylinder is bent
70
Q

Apart from corrective lenses how else to treat astigmatism?

A
  • Rigid contact lenses
  • Surgery
71
Q

1) What is presybyopia and describe the pathophysiology?
2) How to treat presbyopia?

A

1)

  • Loss of accomodation mechanism to adjust to near-sighted vision
  • Loss of lens elasticity
  • In accomodation, the ciliary muscles contract to loosen the lens zonules so theres less tension in the zonules thus the lens due to its elasticity returns to its natural convex shape, thus causing an increase in refractive power and allowing near vision. When there’s a loss of lens elasticity, it can’t return to its convex shape so doesn’t allow the near vision accomodation

2)

  • Just like in hyperopia
  • Use convex lenses to increase refractive power
72
Q

What is the near response triad, and outline the mechanism / process?

A
  • Accomodation process for near vision
  1. Pupillary Miosis (Sphincter Pupillae cause pupils to shrink) to increase depth of field
  2. Convergence (medial recti from both eyes) to align both eyes towards a near object
  3. Accommodation (Circular Ciliary Muscle causes lens to shrink) to increase the refractive power of lens for near vision. Ciliary muscle contracts to loosen the lens zonules so less tension, so lens due to its natural elasticity becomes convex, so gets higher refactive power to allow near vision. Mediated by the oculomotor nerve
73
Q

1) What is intra-ocular lens as correctional treatment?
2) Give 2 times its useful

A

1)

  • Remove any existing lens, or no need if there already is none
  • Then insert a new lens

2)

  1. Replacement of catarct crystalline lens
  2. Aphakia correction (absence of lens for whatever reason)

Y2 - NMH (12 decks)

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