Structure and Function of the Eye (A)

Question 1

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

Answer 1

24 mm

Question 2

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

Answer 2

Sclera  Hard and opaque  Maintains the shape of the eye Choroid  Pigmented and vascular  Provides circulation to the eye  Shields out unwanted scattered light Retina  Neurosensory  Converts light into neurological impulses

Question 3

What are the two segments of the eye separated by?

Answer 3

Lens separates anterior and posterior segments

Question 4

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

Answer 4

Anterior = aqueous humour Posterior = vitreous humour

Question 5

What name is given to the fibrous strands that suspend the lens from the ciliary bodies?

Answer 5

Zonules

Question 6

Describe the production and drainage of aqueous humour.

Answer 6

Aqueous humour is produced by the ciliary body behind the iris. The fluid moves anteriorly around the iris and is drained in front of the iris via 2 pathways: Either the trabecular meshwork into the canals of Schlemm (80-90%, active process) Or uveal scleral outflow (20%, passive)

Question 7

What is the role of aqueous humour?

Answer 7

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

Question 8

Describe the composition of vitreous humour.

Answer 8

99% of vitreous humour is water, trapped in a jelly like matrix

Question 9

What is the function of vitreous humour?

Answer 9

Mechanical support for the eye

Question 10

Describe how the vitreous humour changes with age.

Answer 10

It loses its jelly consistency, liquefies and can become detached from the retina (can shrink basically). Vitreous detachment in seen as floaters in the eyes and is a common problem as people age

Question 11

What are the potentially disastrous consequences of vitreous humour detachment?

Answer 11

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

Question 12

What is the uvea

Answer 12

collective term for the choroid, iris and ciliary body

Question 13

What is the normal range for intraocular pressure?

Answer 13

12-21 mm Hg

Question 14

What is glaucoma?

Answer 14

Optic neuropathy with characteristic structural damage to the optic nerve, associated with progressive RETINAL GANGLION CELL DEATH, loss of nerve fibres and visual field loss

Question 15

What changes can be seen in the retina in glaucoma?

Answer 15

Retinal ganglion cell death Enlarged optic disc cupping (optic cup is the yellowy part of the optic disc)

Question 16

What are the consequences of untreated glaucoma?

Answer 16

Progressive loss of peripheral vision Blindness

Question 17

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

Answer 17

Primary open angle glaucoma Caused by trabecular network dysfunction.

Question 18

Outline the classification of glaucoma

Answer 18

glaucoma can be open angle or closed angle. If the glaucoma is an intrinsic problem then its primary if caused by something else then its secondary (eg eye injury in a fight)

Question 19

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

Answer 19

Small eyes (hypermetropic/long sighted. Light focused behind retina) This is because the structures in the eyes are more crowded and so more likely to block the drainage of aqueous humour. Treatment: peripheral laser iridotomy -otomy means cutting into. Cutting into the iris to create a hole. This allow aqueous humour to flow through the new hole and pushes the iris back so the angle is opened again

Question 20

Describe the structure of the lens.

Answer 20

It has an outer acellular capsule There are regular inner elongated fibres, which give the lens its transparency NOTE: may lose transparency with age

Question 21

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

Answer 21

Cornea = 2/3 Lens = 1/3

Question 22

What layer of the eye is the cornea continuous with?

Answer 22

Sclera

Question 23

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

Answer 23

Physical barrier – protects the eye from opportunistic infection

Question 24

What are the consequences of prolonged contact lens wear?

Answer 24

Reduce the oxygen supply to the cornea

Question 25

What are the 5 layers of the cornea?

Answer 25

1.Epithelium 2.Bowman’s membrane (basement membrane for epithelium) 3. Stroma 4. Descemet’s Membrane (basement membrane of endothelium) 5. Endothelium

Question 26

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

Answer 26

It pumps out fluid from the stroma and prevents stromal oedema

Question 27

What is the role of tear film?

Answer 27

Nutrition of and oxygen supply to the cornea Gliding layer for the eyelids (lubrication) Protection against foreign bodies (dust, pollen, etc.) Smoothing of the optical surface of the eye for clear vision

Question 28

What are the three layers of the tear film?

Answer 28

Superficial oily layer Aqueous tear film Mucinous layer

Question 29

What produces the superficial oily layer?

Answer 29

Meibomian glands

Question 30

What are the roles of each of these three layers?

Answer 30

1.Superficial Oily Layer  Reduces tear film evaporation 2.Aqueous Tear Film  Oxygen and nutrients  Bactericide 3.Mucinous Layer  Ensures that tear film sticks to the eye  Conjunctiva is a transparent layer above the cornea that is very vascular  The conjunctiva has goblet cells that produce mucin which forms part of the tear film

Question 31

what is a closed angle glaucoma

Answer 31

Vicious cycle of increased pressure which pushes the iris/lens forwards, blocking the route of drainage of aqueous humour (trabecular meshwork etc)

Question 32

Which fluid is used in the measurement of intraocular pressure

Answer 32

aqueous humour vitreous humour is fixed so does not really affect pressure that much whereas aqueous humour is affected by the rate of drainage and production so needs to be monitored

Question 33

3 types of tears

Answer 33

Basal tears - constantly produced and make the tear film that is always there reflex tears- irritation causes reflex crying tears

Question 34

outline the reflex pathway of the reflex tears

Answer 34

afferent- V1 of trigeminal (opthalmic) Efferent- parasympathetic nerves neurotransmitter - ACh

Question 35

Outline the pathway of tear production and tear drainage

Answer 35

–Tear produced by the Lacrimal Gland – Tear drains through the two puncta (opening of lacrimal duct located medially) – Tear flows through the superior and the inferior canaliculi (aka lacrimal duct) – Tear gathers in the lacrimal Sac – Tear exits the lacrimal sac into the nasolacrimal duct then into the nasal cavity below the inferior nasal concha

Question 36

Does the conjunctiva cover the cornea?

Answer 36

NO it does not cover the cornea. It only covers the visible part of the sclera and also lines the inside of the eye lids (search up a pic)

Question 37

Sclera water content high or low?

Answer 37

High

Question 38

Cornea water content high or low

Answer 38

low

Question 39

Are there blood vessels in cornea

Answer 39

no

Question 40

Outline the 3 functions of lens

Answer 40

Transparency due to regular structure Refractive power (1/3) Accomodation (its quite elastic)

Question 41

Anterior vs posterior chamber Anterior segment vs posterior segment

Answer 41

Anterior and posterior chambers are part of the anterior segment: Anterior chamber: between cornea and iris Posterior chamber: between iris and lens Anterior segment= everything in front of lens and suspensory ligaments (all aqueous humour) Posterior segment (vitreous chamber)= everything behind lens and suspensory ligaments (all vitreous humour) look at pic in word file