6.2 Histology of the eye

Question 1

What are the 3 layers of the eye?

Answer 1

Corneoscleral
Uveal
Retinal

Question 2

What is the conjunctiva

Answer 2

mucous membrane which covers the exposed part of the eye (sclera and inner surface of the eyelids)

Question 3

What is the function of the conjunctiva

Answer 3

Mucinous secretions add to the protective layer covering the eye
Allow eyelids to move freely over the eye

Question 4

What is the histology of the conjunctiva?

Answer 4

non keratinzing stratified squamous epithelium with goblet cells and scattered melanocytes

Question 5

What is the common presentation of conjunctiva pathology?

Answer 5

Inflammation bilaterally with a red appearance and hyperaemic vesses

Question 6

What divides the eye into chambers?

Answer 6

The lens and iris

Question 7

What do teh anterior and posterior chamber contain?

Answer 7

Aqueous humour

Question 8

How does the aqueous humour circulate?

Answer 8

Produced by the ciliary processes, secreted into the posterior chamber by the ciliary body, circulates through the pupil and drains into the canal of schlemm into the anterior chamber

Question 9

What is the function of the cornea?

Answer 9

Allow entry of light and the principle mechanism for focusing images on the retina

Question 10

What is the junction of the cornea and sclera?

Answer 10

Limbus

Question 11

What are the 5 layers of the cornea?

Answer 11

Epithelium 
Bowmans membrane
Stroma 
Descemet's membrane 
Endothelium

Question 12

What kind of epithelium is the cornea?

Answer 12

stratified squamous

Question 13

Where does the cornea get its nutrients from?

Answer 13

The aqueous humour and environmental oxygen

Question 14

What is ulcerative keratitis?

Answer 14

Inflammation of the cornea from a break in the epithelium

Question 15

Does the cornea have blood vessels?

Answer 15

No

Question 16

What is keratoconus and what causes it?

Answer 16

Bulging of the eyeball due to weak mesenchymal collagen

Question 17

What is the role of the sclera?

Answer 17

Insertion of the extraocular eye muscles, protection and support

Question 18

What is the histology of the sclera?

Answer 18

Dense fibrous avascular tissue which is continuous with the dura surrounding the optic nerve

Question 19

What conditions have a thinning of the sclera?

Answer 19

connective tissue disorders such as marfans, Ehlers danlos and osteogenesis imperfecta

Question 20

What will you see histologically in thinning of the sclera?

Answer 20

Underlying choroidal pigment shows through which will result in a blue colour (normal in newborns)

Question 21

What is the role of the iris?

Answer 21

Regulates the amount of light coming in (aperture control), esures light enters through the pupil

Question 22

What innervates the iris?

Answer 22

ANS

Question 23

What is the iris made of and what are teh surfaces composed of?

Answer 23

Pigmented stromal cells
Anterior: irregular with fibroblasts and melanocytes
Posterior: Smooth pigmented epithelium

Question 24

What determines eye colour

Answer 24

The amount of pigment in the stroma

Question 25

What are the iris muscles?

Answer 25

Dilator pupillae and Constrictor pupillae

Question 26

What orientation are the dilator and constrctor pupillae, what are the made of and what is their innervation?

Answer 26

Dilator: radially oriented made of myoepithelial cells extending from the ciliary body SYMPATHETIC Constrictor: Circumferentially oriented, smooth muscle PARA

Question 27

What is a coloboma?

Answer 27

defect in one of teh structures of the eye

Question 28

What is CHARGE syndrome?

Answer 28

``` Coloboma Heart defects, Atresia of the choanae, Retarded growth and development Genital hyperplasia Ear abnormalaties ```

Question 29

What is aniridia and what causes it?

Answer 29

Absence if the iris - congenital or due to penetrating eye injury

Question 30

What is WAGR syndrome?

Answer 30

Wilms tumour Aniridia Genitourinary abnormalities Retardation

Question 31

What is Mydriasis and what causes it?

Answer 31

Dilation of the pupil - darkness, autonomic neuropathy, trauma, drugs, raised ICP

Question 32

What is the ciliary body?

Answer 32

A continuous thickened ring on the inner surface of the anterior sclera that is a continuation of the choroid

Question 33

What is the function of the ciliary body?

Answer 33

Contains ciliary muscle Permits fine focusing of images on the retina Attaches lens via the zonules Secrete aqueous humour

Question 34

What is the ciliary muscle and what does it do?

Answer 34

smooth muscle which inserts onto the sclera and ciliary body controls the shape of the lens

Question 35

What is the role of the ciliary process?

Answer 35

Anchor the lens into place and form aqueous humour

Question 36

What are the two layers of epithelium of the ciliary processes?

Answer 36

Outer: non pigmented, actively transports aqueous humour Inner: continuous with retina pigmented epithelium

Question 37

What are the zonules?

Answer 37

Fibrillin that attaches the lens to the ciliary process

Question 38

What are the layers of the lens?

Answer 38

Capsule Subcapsular epithelium Lens fibres

Question 39

What is the function of the lens?

Answer 39

Permits focussing on near and far objects | Accommodation in conjunction with ciliary muscles

Question 40

what happens when you focus on a near object?

Answer 40

Ciliary muscles contract causing forwards displacement of the choroid and ciliary body reliving tension on the zonules - lens will round up keeping object in focus

Question 41

What is a cataract and what does it cause?

Answer 41

Opacity of the lens causing light to be scattered and only a small amount transmitted

Question 42

What is glaucoma?

Answer 42

Raised intra-ocular pressure due to obstruction of the flow of aqueous humour

Question 43

What causes open angle glaucoma?

Answer 43

Obstruction of the drainage structures in the angle of the anterior chamber

Question 44

What causes closed angle glaucoma?

Answer 44

Narrow anterior chamber which leads to the peripheral part of the iris compressing the trabecular meshwork

Question 45

What is the function of the choroid?

Answer 45

Supplies nutrients and oxygen to all layers of the eye and absorbs light to prevent light scattering within the eye

Question 46

Where does the choroid lie?

Answer 46

Between the retina and the sclera

Question 47

Where is the vitreous and what is its function

Answer 47

Posterior compartment | Transmits light, supports the lens, holds the retina in place, contributes to intraocular pressure

Question 48

What is the function of the retina?

Answer 48

photoreception conversion of photons into action potential Visual processing

Question 49

What are the 3 types of cells in the retina?

Answer 49

Neurons (ganglion, bipolar, horizontal, amacrine, photoreceptors) Pigmented epithelial cells Neuronal support cells (Muller cells)

Question 50

How many and what are the layers of the retina?

Answer 50

``` 10 Internal limiting membrane Nerve fibre Ganglion cell Inner plexiform Inner nuclear (Muller cells) Outer plexiform Outer nuclear External limiting membrane Photoreceptors Retinal pigmented epithelium ```

Question 51

Where are rods concentrated

Answer 51

outer edge of the retina

Question 52

What is the inner and outer segments of rods made of?

Answer 52

Inner: golgi and mitochondria Outer: flattened membranous discs with rhodopsin

Question 53

What happens with rod loss?

Answer 53

Night blindness and loss of peripheral vision

Question 54

What are cones sensitive to?

Answer 54

blue red and green light

Question 55

What kind of epithelium is the retinal pigmented?

Answer 55

Columnar with basal nucleus

Question 56

What is the function of retinal pigmented epithelium?

Answer 56

Synthesis of melanin that absorbs stray light Phagocytose shed rod discs Support for photoreceptors

Question 57

What fibres form the optic disc?

Answer 57

non myelinated afferent fibres converge medial to the fovea

Question 58

How does the optic nerve form?

Answer 58

Non myelinated afferent fibres converge at the optic disc, penetrate the sclera through the lamina cribrosa to become the optic nerve - become myleinated fibres from the optic disc

Question 59

What is papilloedema?

Answer 59

Swollen optic nerve head secondary to raised intracranial pressure causing disc margins to be blurred but no affect on visual acuity