1.09 Optic nerve head

What are ganglion cells

A type of neurone/nerve cell and their axons gather at the optic disc where they become myelinated aand form the optic nerve

What do ganglion cells do

Connect our eyes to the brain

Label ONH

1. Superficial nerve fiber layer region

2. Prelaminar region

3. Lamina cribrosa region

4. Post/retrolaminar region

What is the lamina cribrosa and its structure

Part of the sclera situated at the site of attachment of the optic nerce.

Its a seive like membrane through which the fibres of the optic nerve pass

Weaker than the rest of the sclera as it has many holes which vary in size and lots of open space (less collagen)

Difference in number of holes at the anterior and postierior face of the lamina cribrosa

Posterior - more holes - 500

Anterior - less holes - 300

A bundle of nerve fibres pasasing through the LC pass through one large hole at the anterior surface and then separate to pass through 2 smaller holes at the posterior surface

What is the lamina cribrosa region defined by

The sclerla fibres that intersect the axon as they exit the eye

Where is the optic nerve head in the superficial nerve fiber layer/prelaminar region

Nerve head lies between the lamina cribrosa and vitreous

What is the retrolaminar region

1st mm of optic nerve behind the eye

Optic nerve head formation

Formed by ganglion cell axons which converge onto the ONH in bundles. Axons in each bundle come from an entire strip of retina over which that bundle has passed

Each bundle is surrounded by other tissue

What does the prelaminar region contain

Most of the tissue around the axon bundle consists of glial cells - specifically astrocytes

What does the post laminar region contain

Contains more connective tissue

Fewer astrocytes

More oligodendrocytes

What do oligodendrocytes do

Produce myelin around axons

What are glial cells

Non neuronal cells in the nervous systen that dont produce electical impulses

What is myelin and its purpose

An insulating layer (sheath) that forms around nerves allowing electrical impulses to transmit quickly and efffeciently

Where are axons myelinated

Myelination is usually only found outside the eye in the post laminar region

Label

1. Papillomacular bundle

2. Raphe

3. Fovea

What is the papillomacular bundle

Bundle of nerve fibres coming from the macula directly

What is the raphe

Point where nerve fibres almost meet

They dont pass from superior to inferior

What is the fovea

The dip at the retina becuase the retinal layers are pushed to the side so light has direct access to photoreceptors

Fovea is avascular, no capillaries, no ganglion cell axons

What are the pale striations in this image

Axon bundles

Label

1. Retinal ganglion cell

2. Glial cell

3. Central retinal vein

4. Central retinal artery

5. Mullers cell

6. Sclera

7. Retinal pigment epithelium

8. Myelinated retinal ganglion cell axon

9. Lamino cribrosa

10. Photoreceptor layer

Label ONH

1. Optic disc edge

2. Neuroretinal rim

3. Optic cup edge

4. Optic cup

What is the neuroretinal rim

Area between edge of cup and disc

Made up of axons of retinal ganglion cells

What is the optic cup

Space with the absence of nerve fibres

What is glaucoma

Loss/damage to retinal ganglion cells which causes the cup to get larger

What is papilloedema

Optic disc swelling

What is considered a small or large optic disc

Small = less than 1.5mm

Large = more than 2mm

What is the outer border of the optic disc made of and how

Collagen

Arises from sclera to join bruchs membrane

What is elschnigs rich

Another word for optic disc border

Volk bio lens correction factors - 90D

x1.32

Volk bio lens correction factors - 78D

x1.08

Volk bio lens correction factors - Super 66

x1.0

Volk bio lens correction factors - 60D

0.87

Volk bio lens correction factors - DIgital wide field

1.39

Volk bio lens correction factors - Superfield

1.30

How to calculate disc size using slit lamp and volk lens

Make slit height the same as the disc height (vertically)

Look at slit height on slit lamp

Slit height x volk lens correction factor (eg 90D = 1.32)

How many nerve fibre axons do we have per eye

Around 1 million

Difference in where axons are packed in small and large discs

In small discs, axons are packed in more tightly as theres a smaller cup and thicker neuroretinal rim

In large discs, axons are around the edge (^opposite reason)

What is the neuroretinal rim

Where the nerves actually are

What forms the neuroretinal rim

The retinal nerve fibre layer

Monocular cues to find the ONH cup

What is the ISNT rule

Tells you in order the thickness of the neuroretinal rim (however some normal eyes may not follow this rule)

Recording CD ratio

Record it horizontally and vertically

CD ratio in relation to glaucoma

Glaucoma is damage to ganglion cell axons so you get more space in the optic disc so CD ratio increases

You get a larger cup (cup is the absence of axons)

How do you know if the cup is deep

Defined colour difference

Can see the pores of the lamina cribrossa

Blood vessels are more blurred deeper in the cup

What is neovascularisation and what is this a sign of

Abnormal growth of new blood vessels

Could be a sign of serious systematic vascular problems or as a result of ocular vascular ‘accidents’

Vascular changes associated with glaucoma

Bayonetting

Baring

Flame haemorrhage

Non vascular changes associated with glaucoma

Notching of the disc

Peripapillary changes

Peripapillary atrophy

What is this

Bayonetting

What is this

Baring

What is this

What is this

Notching

What is this

What is this

What is this

Melanin/pigment

What is this

Thinning of the retina in myopia

Can see the sclera

What is this

Thinning of the retina due in myopia

Can see the sclera

What is this

What is this

What is this

What is this

What can you use as a reference to see if the ONH is normal

Use the other eye as reference

If theyre symmetrical- more likely to be normal

Cup to disc ratio difference of _ is suspicious

More than 0.2

70% of people with glaucoma have unequal CDRs

What to include in ONH recording/assessment

Draw the disc and inner margin of NRR

Vertical length of disc and if its small/medium/large

Horizontal and vertical CDRs

NRR - ISNT

Depth of cup

Add anything abnormal eg pigment, PPA