2.05 OCT of the optic nerve head

What is the optic nerve head

Label

1. Neuroretinal rim

2. Cup

3. Margin

Label

1. NRR

2. Cup

3. Margin

What does ONH margin represent

A break in the retima

All layers stop, no photoreceptors = blind spot

What is the NRR

NRR is the retinal nerve fibre axon bundles passing from the retina into the optic nerve

What is the cup

When the cup is large and deep you can see…

Lamina cribrosa (connective tissue/seive)

Sight threatening diseases associated with optic disc

Life threatening diseases associated with swelling of optic disc

What is this

Papilloedema (swollen disc)

What to record when observing the ONH

What is this

Glaucoma

Notching of ONH

How can we image the ONH

Confocal scanning laser opthalmoscopy

ONH margin is defined by…

Scanning laser polarimetry (GDx)

OCT scans of the ONH 1 - optic disc cube

•Raster scan approach capturing disc and peripapillary area

•Typically ~ 200 x 200 A-scans, 6mm x 6mm on the retina

Can be used to analyse disc topography and surrounding RNFL thickness

OCT scans of the ONH 1 - optic disc cube - ONH topography analysis

For analysis, the “cup” is defined as anything below a reference line

Reference line is set 150μm above the adjacent retinal pigment epithelium

  -this is totally arbitrary!

This analysis mimics subjective ONH analysis

OCT scans of the ONH 1 - optic disc cube - RNFL thickness analysis

OCT scans of the ONH 2 - BMO scans

Sometimes the subjective disc margin (green dots)does not correspond to the actual opening in Bruch’s membrane (red dots).

This analysis can therefore sometimes identify areas of thinner rim than subjectively assessed (e.g. superior & inferior)

Useful in glaucoma

OCT Scans of the ONH 3 - cpRNFL scans

Why is cpRNFL scans useful

OCT Scans of the ONH 3 - cpRNFL scans - what layer thickness does it measure

cpRNFL scans - what do the colours mean when comparing against database

A measurement falling “outside normal limits” means that it is smaller than that measurement for 99% of the healthy eyes in the normative database

It is an indication that disease may be present

•It DOES NOT mean that disease is present!

•Similarly, a measurement “in the green” doesnt mean a disease is not present

•Measurements must always be considered

in context with other clinical findings.

Can change database to match ethnicity

What does the RNFL of this eye show

What does the RNFL of this eye show

What does the RNFL of this eye show

Papilloedema vs optic disc drusen

What is this

Optic neuritis

Optic neuritis appearance

High myopia effect on disc

RNFL of eye with High myopia

What gives misleading RNFL results

RNFL artefacts - unusual discs

RNFL artefacts - Scan capture issues

RNFL artefacts -Segmentation errors

RNFL artefacts - Blood vessels

Monitoring change with OCT

Benefits of OCT

Limitations of OCT