Optic Nerve Head

Question 1

Which of the 12 cranial nerves is the optic nerve/optic disc

Answer 1

Cranial nerve 2

Question 2

Is the optic nerve part of the CNS

Answer 2

Yes

Question 3

Which cells make up the ganglion cell layer

Answer 3

Retinal ganglion cells

Question 4

How many ganglion cell axons is the optic nerve made up of

Answer 4

Approx a million

Question 5

What is the retinal ganglion cell

Answer 5

The retinal ganglion cell is what connects our eyes to the brain, which processes the light signals that the photorecpetors detect.

Question 6

Structure (check lecture for image)

Answer 6

Superficial nerve fibre layer region
Lamina cribrosa region
Retrolaminar region

Question 7

What is the lamina cribrosa

Answer 7

Defined by scleral fibres that intersect the axons as they exit the eye

Question 8

What is the pre-laminar region and post laminar region

Answer 8

Pre-laminar region - nerve head lying between laminar cribrosa and vitreous
Post laminar/retrolaminar region - the first mm of the optic nerve

Question 9

How does the optic nerve head resemble a bunch of cables where the onh is the main cable with many smaller cables within

Answer 9

Ganglion cell axons collected in bundles of several thousands, each surrounded by other tissues - same in all sections of the optic nerve head

Question 10

How does the ensheathing tissues (bits around the axon) vary in prelaminar region and post laminar region

Answer 10

Pre-laminar - most tissue around axon bundles consist of glial cells, specifically astrocytes
Post laminar region - contains more connective tissue so fewer astrocytes and more oligadendrocites which produce the myelin around the individual axon

Question 11

Myelination increases speed of electrical communication between neurones - where is myelination found on the optic nerve

Answer 11

On the optic nerve it is usually only found on the outside of the eye so axons aren’t myelinated inside the eye - usually just the postlaminar region & doesn’t go past laminar cribrosa

Question 12

Structure of laminar cribrosa

Answer 12

• Laminar Cribrosa has a sieve like structure.
• The nerve bundles go through these holes. Because of all the open spaces it is weaker than the rest of the sclera.
• The large hole is where the central retinal artery and vein go through - posterior has more holes than the anterior.

Question 13

Is there any ganglion cells around the foveal region

Answer 13

No they avoid that region

Question 14

What is the papillomacular bundle

Answer 14

Bundle of nerves coming directly from macula area

Question 15

What is the raphe

Answer 15

Point where nerve fibres almost meet - nerve fibres don’t meet from superior to inferior just a midline

Question 16

Diseases that affect the retinal ganglion cells or the optic nerve give distinctive patters of visual loss because…

Answer 16

Of the arrangement of the fibres - arrangement of nerve fibres can show areas of damage

Question 17

Describe the shape and size of the optic disk

Answer 17

Optic disc is not fully circular and is usually longer vertically than horizontally - slightly oval - usually 1.5mm – 2mm

• 2mm is large, <=1.5mm is small

Question 18

What is the optic cup

Answer 18

A depression in the optic nerve head near the centre (aka physiological cup) varying in depth between people
Cup is referring to absence of nerve fibres

Question 19

What is the neuroretinal rim

Answer 19

Where the nerves actually are whereas optic cup is where there is an absence of nerves

Question 20

What is the elschnig/scleral/peripapillary ring

Answer 20

Different names for the ring around the optic disk

Question 21

Structure of the peripapillary ring

Answer 21

collagen which arises from the sclera to join bruch’s membrane - it is the scleral cuff/lip between ONH and choroid and can be considered as the outer border of optic disk. Cant always see it all the way around - sometimes can only see a section of it

Question 22

Retinal nerve fibre layer (RNFL) where are the axons is large discs vs small discs

Answer 22

Large discs - axons around the edge
Small discs - axons packed in more tightly

Question 23

When assessing neuroretinal rim, what rule do we follow

Answer 23

I > S > N > T

Question 24

Cup to Disk Ratio (CD ratio)

Answer 24

When finding cd ratio, use the cup to estimate how many would fit inside the disc. Investigated horizontally and vertically.

Question 25

Why should cd ratio remain constant

Answer 25

A person’s CD ration should remain constant if it enlarges that is a sign of ganglion nerve damage and an indication of glaucoma.

Question 26

How to assess the depth of the cup

Answer 26

In order to assess depth, we can check If we can see the laminar layer. Also, when the depth is larger the colour difference between the cup and the neuroretina rim is more defined. Also take into account to the blur of the blood vessels

Question 27

Things to look out for: Vascular changes at the Disc - vascular changes associated with glaucoma are

Answer 27

Bayoneting Baring Disc haemorrhages

Question 28

Bayoneting

Answer 28

when the vessel forms a 90-degree angle. It is usually due to localised thinning of the neuroretina rim. Blood vessels tend to sit on the rim so whenever there is thinning the blood vessel crosses the sharpens edge of the optic cup.

Question 30

Baring

Answer 30

due to thinning of the neuroretina rim. It still follows the same course, but because it isn’t supported by the rim it appears to be suspended.

Question 31

Flame/disc haemorrhage

Answer 31

haemorrhage at the edge of the disc. Looks like a vein but doesn’t continue further on. Haemorrhages are come and go

Question 32

Non vascular changes associated with glaucoma: notching

Answer 32

area of localised neuroretina rim loss. Neuroretina rim is usually regular in shape.

Question 33

Non vascular changes associated with glaucoma: peripapillary atrophy (PPA)

Answer 33

thinning of the layers in the retina and the retina pigmented epithelium around the optic nerve head. Sometimes seen in healthy people not always a problem, but can be a sign of glaucoma.

Question 34

PPA can be divided into the alpha zone and beta zone - which is closer to the disc

Answer 34

Beta zone closer to the disc

Question 35

Other disc variations not related to glaucoma

Answer 35

Myopia Papilloedema Tilted disc Myelinated nerve fibres Coloboma

Question 36

Myopia

Answer 36

Myopia causes thinning of the retina so can cause choroidal vessels to be seen. The white area is sclera and often shaped as a crescent (myopic crescent). Typically, on the temporal border

Question 37

Papilloedema

Answer 37

Is the swelling of the optic disc. It sticks forward of the retina when viewed binocularly. But monocularly cue is a blurring of the disc margin.

Question 38

Congenital: tilted disc

Answer 38

Nerve leaves the back of the eye at an angle rather than perpendicular

Question 39

Congenital: myelinated nerve fibres

Answer 39

has a white fluffy appearance. Usually, the nerves in the retina are unmyelinated, but some people do have some myelination anterior to the laminar fibrosa. Is usually unilateral 

Question 40

Congenital: coloboma

Answer 40

a congenital abnormality, in which a particular structure in the body doesn’t fully develop, so in this case would be that the optic nerve hasn’t fully developed.