Physiology of the retina

Question 1

What does the lacrimal apparatus consist of?

Answer 1

Lacrimal glands and associated ducts

Question 2

Function of the lacrimal glands

Answer 2

Secrete tears which provide an optically smooth refracting surface
Also contain antibodies and lysozyme to prevent bacterial growth

Question 3

What stimulates lacrimal gland secretion?

Answer 3

parasympathetic stimulation via facial nerve

Question 4

How do tears enter and exit the eye?

Where do they drain?

Answer 4

Enter via the excretory duct
Exit via the lacrimal punctum
Drain into the nasolacrimal duct

Question 5

What is contained in the outer layer of the eye?

Answer 5

Cornea at the front, sclera at the back. Fuses with the dura around the optic nerve

Question 6

What is contained in the middle layer of the eye?

Answer 6

Iris, ciliary body and choroid

Question 7

What is the inner layer of the eye

Answer 7

Retina

Question 8

What type of humour is the cornea filled with?

Answer 8

Aqueous humour (protein free filtrate of blood)

Question 9

What type of humour is the posterior chamber of the eye filled with?

Answer 9

Vitreous humour (watery gel)

Question 10

Function of vitreous humour

Answer 10

Holds shape of eye and maintains focussing accuracy

Question 11

What is the main refractive surface of the eye?

Answer 11

Cornea

Question 12

Is the cornea vasculated and innervated?

Answer 12

Nearly avascular, richly supplied by nerve fibres

Question 13

Function of tears related to the cornea?

Answer 13

maintain oxygen exchange and water content

tears prevent scattering and improve optical quality

Question 14

How do the exterior and interior of the sclera differ?

Answer 14

Exterior is smooth and white

Interior is brown and grooved

Question 15

Rough diameter of average pupil?

Answer 15

3-7mm

Question 16

What is the conjuctiva

Answer 16

layer of stratified columnar epithelium, goblet cells and capillaries that covers the sclera

Question 17

Function of goblet cells in the conjuctiva?

Answer 17

Produces mucus that mixes with tears

Question 18

Where is the blind spot?

Answer 18

The point where visual axons leave the eye to form the optic nerve (no photoreceptors here)

Question 19

Where does aqueous humour drain?

Answer 19

Canal of Schlemm

Question 20

How is intraocular pressure formed?

Answer 20

Difference between formation and drainage of aqeuous humour

Question 21

Name the the 2 main sub groups of glaucoma?

Answer 21

Open angle glaucoma

Primary angle closure glaucoma

Question 22

What is open angle glaucoma?

Answer 22

Slowly progressive condition, trabecular meshwork gradually becomes blocked
Normal angle between cornea and iris

Question 23

What is primary angle closure glaucoma?

Answer 23

Angle between cornea and iris is reduced
Flow of fluid cannot pass through canal of Schlemm
Causes rapid increase

Question 24

Describe the surgery that can be used to treat glaucoma

Answer 24

Incision mae at cornea-sclera junction

Question 25

What is the fovea?

Answer 25

The point where the cones are most closely packed

Question 26

What type of cells are present in the fovea?

Answer 26

Cones

Question 27

How many types of cone cells are there?

Answer 27

3

Question 28

Function of rod cells?

Answer 28

Very sensitive to light- active in the dark. no colour differentiation, suppressed in daylight

Question 29

Which part of the rods and cones are photoreceptive?

Answer 29

the outer segment

Question 30

What is contained in the inner segment of the rods and cones

Answer 30

Cell body and synaptic terminal

Question 31

Describe the structure of the outer segment of rod cells

Answer 31

Consists of disks of membrane containing the photopigment ‘rhodopsin’

Question 32

What protein is contained in cone cells?

Answer 32

Cone opsins

Question 33

What is the advantage of the stacking arrangment of rod cells?

Answer 33

The light passes through all the segments in sequence, maximising the chance of a photon interacting with molecule of pigment

Question 34

How can cones afford to have a shorter outer segment

Answer 34

There enough light in the daylight to guarentee a photon with interact with a photopigment

Question 35

Why does the eye require such high amounts of oxygen?

Answer 35

Because photoreceptors are one of the most metabolically active cells in the body

Question 36

How does the cells of the eye remain depolarised?

Answer 36

Constant inward leak of sodium keeps cell depolarised and toonically release glutamate from synaptic ending

Question 37

What is the effect of light on eye cells?

Answer 37

Hyperpolarises the cell and stops the tonic glutamate release

Question 38

What is the effect of light absorption of the rhodopsin?

Answer 38

Changes the shape
This acts via G protein coupled receptor to reduce level of cyclic GMP in rod
This closes sodium channel and allows cell to stop releasing glutamate
Light is an inhibitory stimulus

Question 39

What is the role of bipolar cells?

Answer 39

Converts this continuous release of glutamate into varying depolarisation. This is transmitted to ganglion cells which project axons into the optic tract

Question 40

Three main neurons in the path from photoreceptor to optic nerve?

Answer 40

Photoreceptor
Bipolar cells
Ganglion cells

Question 41

What is the blood supply of the inner retina?

Answer 41

Central retina artery

Question 42

What is the blood supply of the photoreceptors?

Answer 42

Supplied by choroid (network of capillaries suppled by ciliary arteries)