Structure & Function of Eye - Part 1

Question 1

Three types of tears

Answer 1

Basal tears
Emotional tears
Reflex tears

Question 2

What is the afferent pathway for reflex tear production?

Answer 2

Opthalmic branch of trigeminal nerve (V1)

Question 3

What is the efferent pathway for reflex tear production?

Answer 3

PNS

Question 4

What are the three layers of basal tears?

Answer 4

Superficial lipid layer 
Aqueous layer (tear film)
Mucin layer (continuous with cornea)

Question 5

What produces the superficial layer of tears and what is this layer’s function?

Answer 5

Meibomian glands produce oily layer, which prevents evaporation of tears

Question 6

What produces the tear film?

Answer 6

Tear glands

Question 7

List four functions of the tear film

Answer 7

Bactericide
Debris removal
Oxygen supply to cornea
Maintenance of smooth cornea-air surface

Question 8

Which structure covers the cornea?

Answer 8

Conjunctiva

Question 9

Describe how the conjunctiva is distributed

Answer 9

Begins at outer edge of cornea
Covers eye
Lines inside of eyelid

Question 10

Describe the properties of conjunctiva

Answer 10

Transparent tissue

Nourished by nearly invisible blood vessels

Question 11

Describe the outermost structure of the posterior segment of the eye

Answer 11

Sclera

• opaque
• maintains eye shape
• tough
• high water content

Question 12

Describe the properties and function of the choroid

Answer 12

Vascular
Pigmented
Provides circulation
Shields unwanted scattered light

Question 13

Describe the properties and function of the retina

Answer 13

Neurosensory

Translates light into neural impulses

Question 14

Describe the flow of tears

Answer 14

Produced by lacrimal gland 
Covers eye 
Drains into punctum 
Travels via superior and inferior canaliculi into:
Tear sac
Tear duct 
Nose

Question 15

What is continuous with the sclera?

Answer 15

Cornea

Question 16

Describe the properties of the cornea

Answer 16

Transparent 
Convex
Does 2/3 of refraction (higher refractory index than air)
Physical barrier 
Infection barrier

Question 17

State the five layers of the cornea

Answer 17

Epithelium 
Bowman's membrane 
Stroma 
Descemet's membrane 
Endothelium 

(Every blue sky deserves notice)

Question 18

Which layer of the cornea provides nutrients to the other layers and how?

Answer 18

Stroma - nerve endings provide nutrients as there is no blood supply in the cornea

Question 19

Describe the function of the endothelium in the cornea

Answer 19

It pumps fluid out of cornea, preventing cerebral oedema

Question 20

What may result from endothelial cell dysfunction?

Answer 20

Corneal oedema

Corneal cloudiness

Question 21

Describe some properties of the endothelium

Answer 21

1 cell thick

No regeneration power

Question 22

What is the uvea and what three things is it composed of?

Answer 22

Vascular coat of eye between sclera and retina, composed of:

Iris
Ciliary body
Choroid

Question 23

Which part of the eye has a similar function to controlling the aperture on a camera? Describe the function of this structure.

Answer 23

IRIS - controls light levels

Question 24

What two muscles make up the iris and what are their functions?

Answer 24

Sphincter pupilae (Circular muscle): Constricts pupil

Dilator pupilae (raDIAL muscle) - DILAtes pupil

Question 25

Describe the structure of the lens including its outer and inner layers

Answer 25

Outer acellular layer Inner layer of elongated cell fibres Biconvex

Question 26

What is the lens made of which gives it its transparency?

Answer 26

Transparent collagen

Question 27

What is the significance of having elongated cell fibres?

Answer 27

Enables elasticity for accommodation

Question 28

Which action fattens the lens?

Answer 28

Contraction of ciliary muscles PUSHES the lens zonules, making the lens fatter

Question 29

Which action flattens the lens?

Answer 29

Relaxation of ciliary muscles PULLS the lens zonules, making the lens flatter

Question 30

What refractory power does the lens have?

Answer 30

1/3 | the other 2/3 is provided by the cornea

Question 31

What is the optic disc?

Answer 31

The visual portion of the optic nerve

Question 32

Where does the optic nerve connect to?

Answer 32

Near the macula

Question 33

What is the macula?

Answer 33

The middle of the retina, responsible for detailed central vision

Question 34

What is the fovea

Answer 34

The central part of the macula which enables detailed vision

Question 35

Describe the difference in fluid composition in the two segments of the eye

Answer 35

Anterior segment - aqueous humour | Posterior segment - vitreous humour

Question 36

What forms the axis by which the segments are divided in the eye?

Answer 36

Lens Anterior segment is anterior to the lens (between cornea and lens) Posterior segment is behind lens

Question 37

What are the two outflows of aqueous humour? Which of these is passive?

Answer 37

Trabecular meshwork-canal of Schlemm (90%) | Uvea-scleral flow (10%) - passive

Question 38

Describe the flow of aqueous humour

Answer 38

``` Produced by ciliary body Flows anteriorly into anterior chamber Supplies nutrients Drains via trabecular meshwork Into canal of Schlemm ```

Question 39

What is the consequence of having a raised IOP in glaucoma?

Answer 39

Death of retinal ganglion cells; visual field loss; blindness

Question 40

What can be seen in the retina of someone with glaucoma?

Answer 40

Enlarged optic disc 'cupping' as a result of damage to the optic nerve

Question 41

State the two types of glaucoma. Which of these is more common?

Answer 41

``` Open angle (most common) Closed angle ```

Question 42

What causes open angle glaucoma?

Answer 42

Trabecular meshwork dysfunction

Question 43

What causes closed angle glaucoma?

Answer 43

Increased IOP pushes lens and iris forwards, blocking the trabecular meshwork

Question 44

How might closed angle glaucoma present?

Answer 44

Sudden painful red eye with acute drop in vision (normally their mind fills in the image even if they can't see)

Question 45

What are the risk factors of CAG?

Answer 45

Hypermetropia (small eye) | Pre-existing narrow angle at TM

Question 46

How is closed angle glaucoma treated?

Answer 46

Peripheral laser iridotomy (drainage hole in iris)