Structure and function of the eye

Question 1

What does the eye sit within?

Answer 1

The orbit

Question 2

What are the three layers of the coat of the eye?

Answer 2

Sclera, choroid and retina

Question 3

What is the sclera like and what does this help?

Answer 3

Hard and opaque- protects the eye and maintains its shape

Question 4

What is the choroid like and what does it do?

Answer 4

It is pigmented and vascular and provides circulation to the eye and retina

Question 5

What is the retina like and what does it do?

Answer 5

Neurosensory tissue- converts light into nerve impulses which are transmitted to the brain via the optic nerve

Question 6

What are the anterior and posterior segments of the eye separated by?

Answer 6

Lens

Question 7

What sort of humour is in the anterior and posterior segments?

Answer 7

Anterior- aqueous

Posterior- vitreous

Question 8

What are zonules?

Answer 8

Fibrous strands that holds the lens in place in line with the pupil- they are connected to ciliary muscles

Question 9

What does the ciliary body produce?

Answer 9

Aqueous humour

Question 10

Where does aqueous humour go after production?

Answer 10

Passes into the anterior chamber and then drains out through the angle via trabecular meshwork

Question 11

What is this drainage important for?

Answer 11

Maintaining intraocular pressure

Question 12

What is the aqueous fluid important for

Answer 12

Supply nutrients to the cornea and other tissues in the anterior chamber

Question 13

What is unique about the middle part of the eye?

Answer 13

No blood vessels as you need a clear window for light to pass through

Question 14

What is the posterior segment located between?

Answer 14

Lens and retina

Question 15

The vitreous humour is made up of 99% water trapped inside a jelly matrix, what is the jelly matrix for?

Answer 15

Mechanical support to the eye

Question 16

What is happening when you see floaters?

Answer 16

The vitreous humour is detaching, as we get older, the vitreous humour loses its jelly constituency, liquefies and detaches from the retina

Question 17

What can go wrong with vitreous humour detachment?

Answer 17

It can lead to a small tear in the peripheral retina, the liquid vitreous could pass into the sub retinal space and lead to detachment which requires prompt treatment or can lead to blindness

Question 18

What is the name of the ring shaped tissue surrounding the lens

Answer 18

Ciliary body

Question 19

What are the two layers of the iris and what are they composed of?

Answer 19

Anterior- Stromal layer containing muscle fibres

Posterior- Epithelia

Question 20

What is the uvea made up of?

Answer 20

Choroid, ciliary body and iris

Question 21

What is the normal intraocular pressure

Answer 21

11-12 mmHg

Question 22

What is glaucoma?

Answer 22

Condition of sustained intraocular pressure

Question 23

What does glaucoma result in?

Answer 23

Accumulative damage to the optic tissue

Retinal ganglion cell death and enlarged optic disc cupping

Question 24

What is the commonest form of glaucoma?

Answer 24

Primary open angle glaucoma

Question 25

What is primary open angle glaucoma caused by?

Answer 25

Functional blockage of trabecular meshwork

Question 26

What is closed angle glaucoma caused by?

Answer 26

Forward displacement of the iris/lens complex narrowing the trabecular meshwork

Question 27

What sort of patients does closed angle glaucoma occur commonly in?

Answer 27

Small eyed patients (hypermetropic)

Question 28

What is the lens made up of and what function does this have?

Answer 28

Regular inner elongated cell fibres- transparency

Question 29

What fraction of the eye's refractive power is the lens responsible for?

Answer 29

1/3

Question 30

What is accommodation?

Answer 30

The lens can change shape so it can alter its refractive power and ability to focus can change so it allows you to focus on near or distant objects

Question 31

What is a cataracts?

Answer 31

When the lens loses its transparency

Question 32

Where is the cornea in the eye?

Answer 32

Front most part of the anterior segment

Question 33

What is there cornea continuous with?

Answer 33

Sclera

Question 34

What fraction of the eyes refractive power is the cornea responsible for?

Answer 34

2/3

Question 35

What is the function of the front surface of the cornea

Answer 35

Physical barrier

Question 36

What are the three main layers of the cornea?

Answer 36

Epithelium, stroma and endothelium

Question 37

What is the stroma responsible for?

Answer 37

Transparency

Question 38

What does the endothelium do?

Answer 38

Pumps fluid out of the stroma and prevents stromal oedema

Question 39

What is the tear film?

Answer 39

Thin layer of fluid that covers the cornea

Question 40

What is the tear film important for?

Answer 40

Maintaining clear vision and removing surface debris during blinking Source of oxygen and nutrients to anterior segment Bactericide

Question 41

What are the three layers of the tear film?

Answer 41

Superficial oily layer Aqueous tear layer Mucinous layer

Question 42

What does the superficial oily layer do?

Answer 42

Reduces tear film evaporation

Question 43

What is the superficial oily layer secreted by?

Answer 43

Melbomian glands along the lid margin

Question 44

What does the aqueous tear film do?

Answer 44

Delivers oxygen and nutrients to surrounding tissues and contains bactericide

Question 45

What does the mucinous layer do?

Answer 45

Maintains surface wetting | Ensures that the tear film sticks to the eye

Question 46

How do mucin molecules act?

Answer 46

Binding water molecules to the hydrophobic corneal epithelial cell surface

Question 47

What is the conjunctiva?

Answer 47

Transparent layer on top of the surface of the cornea that is very vascular- it has goblet cells that produce mucin

Question 48

Where is the lacrimal gland situated?

Answer 48

Within the orbit, latero-superior to the globe

Question 49

What are the three types of tear that the lacrimal gland produces?

Answer 49

Basal tears- produced at constant level Reflex- In response to irritation Emotional- crying

Question 50

What is the tear reflex pathway?

Answer 50

Irritation is detected by the incredibly sensitive cornea which is innervated by the sensory fibres from the ophthalmic branch of the trigeminal nerve and the efferent pathway is mediated by a parasympathetic nerve that innervates the lacrimal gland

Question 51

What regulates light entry into the eye?

Answer 51

Pupil and pigmented uvea

Question 52

What maintains the shape of the eye?

Answer 52

Scleral coat

Question 53

What is emmetropia

Answer 53

Perfect focusing, parallel rays converge directly on the fovea forming a clear image

Question 54

What is hypermetropia more commonly known as?

Answer 54

Long sighted

Question 55

Where do the light rays focus in hypermetropia?

Answer 55

Behind the retina

Question 56

What is myopia?

Answer 56

Short sighted

Question 57

Where do the light rays focus in myopia and why?

Answer 57

In front of the retina- cornea and lens have excess refractive power

Question 58

What sort of lens do people with myopia require to see objects far away?

Answer 58

Concave

Question 59

What is the cornea like in astigmatism?

Answer 59

The cornea is oval shaped instead of spherical

Question 60

Describe the mechanism of accommodation

Answer 60

The circular ciliary muscles within the ciliary body contract which leads to relaxation of the zonules so the lens returns to its natural convex shape and increases the refractive power of the lens

Question 61

Which nerve is accommodation mediated by?

Answer 61

Efferent oculomotor nerve

Question 62

What are the three pathways of the near response triad for near vision?

Answer 62

Pupillary miosis (constriction)- increases depth of field Convergence Accommodation

Question 63

What is presbyopia?

Answer 63

Naturally occurring loss of accommodation with age

Question 64

What happens at the optic disc?

Answer 64

Retinal ganglion cells leave the eye via the optic nerve

Question 65

What is important about the macula?

Answer 65

It has the highest concentration of photoreceptors so is vital for fine vision

Question 66

What are the four branches of vessel arcades that radiate from the optic disc?

Answer 66

Superior temporal Inferior temporal Superior nasal Inferior nasal

Question 67

When looking at an eye, how can you tell the difference between an artery and vein?

Answer 67

Veins are darker and thicker

Question 68

Where do the retinal arteries and veins provide circulation to?

Answer 68

Inner 2/3 of retina

Question 69

What provides circulation to outer 1/3?

Answer 69

Choroidal vasculature

Question 70

What sort of vision is the fovea responsible for and why?

Answer 70

Central- Detailed day/colour vision - it is the area with the highest concentration of cones

Question 71

How do you assess fovea function?

Answer 71

Visual acuity test

Question 72

What is peripheral vision used for?

Answer 72

Shapes, movement and night vision

Question 73

How is peripheral vision assessed?

Answer 73

Visual field assessment

Question 74

What are the two layers of the retina?

Answer 74

Outer layer- Retinal pigment epithelium | Inner layer- Neuroretina (made up of photoreceptors and neurones)

Question 75

What is the function of the retinal pigment epithelium?

Answer 75

Transports nutrients from the choroid to the photoreceptor cells and removes metabolic waste from the retina

Question 76

What are the three divisions of the neuroretina?

Answer 76

Outer layer- photoreceptors Middle layer- bipolar cells (axons project in both directions) Inner layer- retinal ganglion cells

Question 77

What is the fovea anatomically characterised by?

Answer 77

Foveal pit- it is there due to the lack of overlying ganglion cell layer

Question 78

What is the main structural difference between cones and rods?

Answer 78

Rods have longer outer segments

Question 79

How many cones and how many rods are there roughly?

Answer 79

120 million rods | 6 million cones

Question 80

What is the rod photopigment?

Answer 80

Rhodopsin

Question 81

What is another term for night vision?

Answer 81

Scotopic vision

Question 82

Where is the highest density of rod receptors?

Answer 82

Just outside the macula

Question 83

Where is there no rod receptors?

Answer 83

Macula

Question 84

On the frequency spectrum, how many peaks does the rod photopigment(s) have?

Answer 84

One peak- 498nm (blue/green)

Question 85

How many peaks does the cone photopigments(s) have

Answer 85

Three peaks S-cone - 420-440nm (blue) M-cone - 534-545nm (green) L-cone - 564-580nm (red)

Question 86

What is the commonest form of colour blindness?

Answer 86

Deuteranomaly (red-green colour blindness)

Question 87

What is deuteranomaly caused by?

Answer 87

Shifting of M cone peak towards L cone peak

Question 88

What is an anomalous trichromatism?

Answer 88

When a vision deficit is caused by a shifted frequency peak

Question 89

What is monochromatism?

Answer 89

Complete absence of colour vision

Question 90

What is a common test used to test for colour blindness?

Answer 90

Ishihara

Question 91

What happens to rod receptors in daylight?

Answer 91

They are suppressed to reduce sensitivity to light