Special Senses 2

Question 1

What are the 3 layers of the eye?

Answer 1

Corneoscleral coat - outermost
Uveal tract - middle
Retina - inner

Question 2

Structure of the uveal tract

Answer 2

Consists of iris and ciliary body anteriorly

Vascularised choroid coat posteriorly

Question 3

Structure of the retina

Answer 3

Layers of nerve cells, their processes, support cells and on the outside a layer of pigmented epithelium

Question 4

Properties of the lens

Answer 4

Biconvex

Elastic to allow change in shape permitting near vision

Question 5

What is in front of the lens?

Answer 5

Two chambers (anterior and posterior) filled with aqueous humor

Question 6

What is posterior to the lens?

Answer 6

Much larger vitreal cavity filled with vitrous humor which is avascular and gelatinous

Question 7

What is the conjunctiva?

Answer 7

A thin transparent mucous membrane

Question 8

What lines the conjunctiva?

Answer 8

Stratified columnar epithelium with goblet cells and has a lamina propria of loose connective tissue

Question 9

Where is the conjunctiva?

Answer 9

From the corneoscleral margin and reflects over the inner surface of the eyelids

Question 10

What is the cornea?

Answer 10

Outer layer of thin non keratinised stratified squamous epithelium sitting on Bowmans membrane

Question 11

What is the Bowman’s membrane?

Answer 11

A thin layer of collagen composed of randomly oriented, condensed thin collagen fibrils

Question 12

What is the corneal stroma?

Answer 12

Many layers of precisely oriented, hydrated collagen with each layer at roughly right angles to eachother
There are corneal fibroblasts between layers

Question 13

What is the Duscemet’s membrane?

Answer 13

A layer of endothelium sitting on a layer of meshwork collagen

Question 14

What is a kaiser-fleischer ring?

Answer 14

An accumulation of copper in duscemet’s membrane at the corneo-scleral junction
Most often seen in Wilson’s disease

Question 15

What is the sclera?

Answer 15

Tough coat of collagen and elastic fibres defining the globe

Where the tendons of the extraocular muscles attach

Question 16

What is the ciliary body?

Answer 16

Contains smooth muscle that releases tension on zonular fibres during near vision allowing lens to round up due to its natural elasticity

Question 17

What is the canal of Schlemm?

Answer 17

Where excess fluid from the anterior chamber is drained

When drainage is not adequate = glaucoma

Question 18

What is the iris?

Answer 18

Mostly loose connective tissue with a layer of pigmented epithelium on its posterior surface
Contains melanocytes and smooth muscle which changes its diameter

Question 19

How do you produce blue and brown eyes?

Answer 19

Abundant melanocytes = brown eyes

Few melanocytes = blue eyes

Question 20

What do sphincter pupillae fibres do?

Answer 20

Located near tip of iris and circumferentially oriented

Constrict pupil under parasympathetic stimulation

Question 21

What do dilator pupillae muscles do?

Answer 21

Radially oriented

Open pupil under sympathetic stimulation

Question 22

What is the flow of aqueous humor?

Answer 22

Secreted by ciliary processes into posterior chamber

Flows between iris and lens to reach anterior chamber

Question 23

Structure of the lens

Answer 23

Made of lens fibres - cellls that lose nuclei and organelles as they mature and are packed with crystallins
Anteriorly covered by connective tissue capsule and layer of simple cuboidal epithelium

Question 24

During development where are new lens cells produced?

Answer 24

At the lateral margin of the lens - the germinal zone

Question 25

Structure of lens fibres

Answer 25

Long Run in an arc anterior to posterior Roughly hexagonal in cross section Densely packed together

Question 26

How many rods and cones does the retina contain?

Answer 26

130,000,000 rods | 6,500,000 cones

Question 27

What do rods contain?

Answer 27

Rhodopsin - a light sensitive pigment | Usually for low light vision

Question 28

What do cones contain?

Answer 28

One of 3 opsin pigments sensitive to either red green or blue light Red - long wavelength Green - medium wavelength Blue - short wavelength

Question 29

What are the layers of the retina?

Answer 29

``` Inner limiting membrane Layer of optic nerve fibres Ganglion cell layer Inner plexiform layer Inner nuclear layer Outer plexiform layer Outer nuclear layer Outer limiting membrane Rods and cones Retinal pigment epithelium Lamina vitrea Choroid ```

Question 30

Where is the fovea?

Answer 30

At the centre of the optical axis on the retina

Question 31

Where is the foveola?

Answer 31

At the centre of the fovea

Question 32

What is the foveola?

Answer 32

Where the retina thins and is avascular Only cones found here covered only by outer plexiform layer Very high acuity vision

Question 33

What is the optic disc?

Answer 33

The site where the axons of the retinal ganglion cells exit the eye to form the optic nerve

Question 34

Why is the optic disc known as the blind spot?

Answer 34

Lacks photoreceptors

Question 35

What are the lamina cribosa?

Answer 35

A series of openings in the sclera that fibres which will form the optic nerve exit through the eyeball

Question 36

What is the red eye effect?

Answer 36

Mainly due to blood supply in choroid | More intense in pale people with blue eyes as they have less melanin in pigmented epithelium