Lecture 2: The eye

Question 1

Describe innervation of the orbital muscles:

Answer 1

LR 6
SO 4
Rest is CN 3

Question 2

Describe the innervation of the eyelids:

Answer 2

Obicularis oculi closes the eye and is innervated by CN7

Levator palpebrae opens the eye and is innervated by CN3 (occulomotor)

Question 3

Describe the tear film:

Answer 3

The tear film is comprised of 3 layers;

• > Oil (Tarsal gland, stops evap)
• > Aquous (lacrimal gland, tears)
• > Mucus (Goblet cells of conjunctiva)

Question 4

What is the lacrimal system?

Answer 4

Lacrimal gland produces tears, this and blinking washes debris down to the puncta where they can drain into the lacrimal duct.

Question 5

Describe the optical component of the eyes:

Answer 5

Light is refracted slightly by the cornea (2/3 focusing) and then again by the lens (1/3 focusing) to be focused on the retina.

The pupil dilates etc to control the amount of light entering the eye.

Question 6

What is an astigmatism?

Answer 6

When there is two focal points on the retina

Question 7

What is myopia?

Answer 7

Short sightedness

Question 8

What is hyperopia?

Answer 8

Long sightedness

Question 9

Describe the physiology of the eye and its relation to maintaining shape:

Answer 9

Hyaluronin in the eye is hydrophilic and drags in water

Epithelium of the cornea pump ions to keep the cornea relatively dehydrated ensuring good shape is maintained.

Intra-occular pressure also aids maintaining shape.

Lamellar of collagen fibres are arranged orthogonally. (strength)

Question 10

How is the lens suspended?

Answer 10

By the zonules of zen to the ciliary bodies

Question 11

Loosely describe the lens structure?

Answer 11

Centre = nucleus

Layers of cells are deposited over life

Question 12

What are cataracts and their classification?

Answer 12

Cataracts are opacities

• Cortical or nucelar
• Senile or juvenile
• Diabetic or traumatic

Question 13

Describe the cilliary body:

Answer 13

Circular layer (seen inner circle and outer) (constricts) 
Longitudinal layer (dilates)

Question 14

What is accomodation?

Answer 14

Contraction of the ciliary muscles to increase the curve of the lens and increase refraction allowing near sightedness.

Presbyacusis is loss of accomodation with age.

Question 15

What is the aquous humor? where is it? what does it do? what produces it?

Answer 15

• Fills space between lens and iris. (ant. chamber)
• Epithelium on ciliary body produce aq. humor
• Nourishes lens and cornea which are avascular.
• Maintains shape and pressure of ant. chamber
• Flows out through the trabecular mesh network and when this is damaged, it impedes flow.

Question 16

What is the fovea of the reina?

Answer 16

Centre of visual acuity

Question 17

Describe the fovea:

Answer 17

• Has no ganglion cells infront of it or blood vessels
• Contains only cones
• Light hits the cones directly.
• Offset from the optic disc (which is just where the optic nerve connects)

Question 18

Why is the retina back to front so to speak?

Answer 18

So that the rods and cones are closest to the nutrient source as they are the largest consumers and waste producers relatively in the body.

Question 19

Describe the function of the bipolar cells of the retina:

Answer 19

Bipolar cells; Like multiplug board

Question 20

How does the central and peripheral retina compare?

Answer 20

Central retina has a much higher density of photoreceptors

Question 21

What is the macula lutea?

Answer 21

Area surrounding the fovea and contains many Xanthophyll caratenoids - Zeaxanthin and lutein which are protective in function.

Question 22

What is found at the optic disc / nerve?

Answer 22

No photoreceptors.
Just ganglion cells for inputs

Question 23

Describe the relative rods and cones density of the retina:

Answer 23

Cones are highest density in the fovea and relatively low everywhere else.

Rods are not present in the fovea but increase in density from the peripheral towards the fovea.

Question 24

What do rods and cones do?

Answer 24

Cones = visual acuity 
Rods = movement detection / low light

Question 25

What is keratoconus?

Answer 25

• Thin epithelium
• Loss of matrix
• Loss of keratocytes
• Loss of stromal integrity

Time for corneal replacement / surgery

Question 26

What are some methods to surgically enhance the cornea?

Answer 26

Corneal graft
Relaxing incisions
Stromal insertions
Crosslinking

Question 27

What are some regenerative medicine techniques for improving the cornea?

Answer 27

Corneal engineering
Gene therapy
Stem cell therapy

Question 28

Describe corneal engineering:

Answer 28

• In vitro engineering of cell layers
• Cells plus scaffold
• Artificial corneas

Question 29

Describe the generic retina:

Answer 29

3 layers of cell bodies, 2 layers of synapses

i.e

Pig. epithelum
-> Cell bodies of rods/ cones
(outer nuclear layer, i.e synapse with bipolar cells)
-> Cell bodies of bipolar cells
(Inner nuclear layer i.e synapse with ganglion cells)
-> Cell bodies of ganglion cells

Question 30

Why is rhodopsin clinically relevant?

Answer 30

GPCR of rod cells, it is used as a biomarker of retinal thinning and degeneration

Question 31

What do rods do?

Answer 31

Low light levels (Scotopic)
Peripheral vision
Slow response

Question 32

What do cones do?

Answer 32

Visual acuity
Colour vision
Fast response

Question 33

Answer 33

Question 34

Answer 34

1. Trochlea

2.

Question 35

Answer 35

Question 36

Answer 36

Question 37

Answer 37

Question 38

Answer 38

Question 39

Answer 39

Question 40

Answer 40

Question 41

Answer 41