week 11 co2 - oct

What are the basic principles of OCT imaging?

• 3D imaging technique with high spatial resolution

• Large penetration depth even in highly scattering media

• Based on measurements of reflected light from tissue discontinuities

• Based on interferometry (interference between incident and reflected light)

• Uses long wavelength light instead of of sound (3×10^8 m/sec)

How does the OCT image form?

• layers and structures backscatter and reflect light at varying degrees

• Refractive index variations cause contrast differences

• Reflected light analysed

• Image can be presented as 2D or 3D greyscale or false coloured image

Label this OCT scan

Which colours in colour coding OCT are most reflective?

White/red (bright colours)

Intermediate reflectivity - greeen

Low reflectivity - dark colours

How many scans to form a 2D B-scan?

30k A scans aligned In macular image

What can b-scans be used for?

3D image

What were early developments of OCT?

• were time domain - time in difference in reflectance was analysed - slow

• Spectral/fourier-domain (FD) - detects oscillations - high resolution and faster

What is the latest technology of OCT?

Swept source

• longer wavelength of light - deeper pentretration of deeper layers

• Better image past cataract

• Faster - more scans in given time

What’s the resolution of OCT?

2-10 micrometers

What are uses of OCT in practice?

• Retina: Macular hole, macular oedema, retinal

detachment, epi-retinal membrane etc.

• Optic neuropathies, e.g. glaucoma: Nerve fibre layer thickness can be measured

• Anterior segment: Anterior chamber angle, cornea et

What are limitations of OCT scans in practice?

•Image affected by dense media opacities

•Px co-operation

• moving or blinking px will affect image

•Operator error - Must place instrument over pathology- be guided by fundus appearance

•Does not replace ophthalmoscopy

Label this diagram

Learn this

What is this?

Dry ARMD

What are characteristics of dry ARMD in an OCT scan?

•Characterised by drusen

•Bright, hyper-reflective elevations of RPE

•Retinal thinning

What is this?

Wet ARMD

What are the characteristics of wet ARMD in an OCT scans?

• Development of choroidal neovascularization (CNV) in sub-RPE space

• Detachment of RPE from choroid- ischaemia

• Symptoms metamorphopsia - waviness or

shimmering

What is the epiretinal membrane?

• Fibrous membrane forms along ILM

• This can shrink and cause the retina to wrinkle or pucker

• VA often not affected

What is this?

Retinal detachment

How do retinal detachment occour?

Neurnseosory retina separates from RPE

How can you view retinal detachment in OCT?

Px may have to

view peripheral

poinT

What are examples of diabetic retinopathy?

•Haemorrhages, exudates

•Inner retina

•Macular oedema

• Subretinal fluid

• Intra-retinal cysts

What is this?

Macular hole

What information can an OCT give you about the ONH?

•Quantitative measurements of optic disc topography and RNFL measurements

• Cup volume

• Disc area

• Cup and rim area

• C/D ratio

• RNFL thickness – yellow (borderline) and

red (abnormal - thinner than normal) - compared to normative database

What is this?

• OCT of the anterior angle

• Grade 3

• Grade 1 -closed - refer

Should you do associated before dissociative tests?

Yes

Eg mallet unit before Maddox rod

Why do you view the anterior eye in an OCT?

•Assessment of A/C

angle

•Corneal pathology

•Contact lens fittinG

What is this and what does it do?

OCT-A optical coherence Tomography angiography

•Shows blood flow in retinal vessels

• Ability to detect and monitor vascular anomalies

•Unlike fluorescein angiography, it does not show leakage from vessel

What is ultra wide field (UWF) imaging?

•Traditional cameras capture 30-50 degrees

•Photomontages were created to increase

the FOV beyond this

•Time-consuming

•Demanding of px

How many degrees can UWF imaging view?

Up to 200 degrees possible

Learn this

Learn this

What is the technology behind confocal Asher scanning microscopy?

• The illuminating system is a laser beam with cross section 10-20μm

• The viewing system is a photocell

• Horizontal and vertical mirrors allow fast scanning of the laser beam

• Reflected light from the retina builds up an image of the Fundus

• Confocal means that v small viewing apertures restrict the view to the area directly illuminated by the laser

• Changing the focus allows different layers to be

visualise

What do green lasers scan from?

• The sensory retina to the pigment epithelial layers

• Accentuates retinal blood vessels

What do the red lasers scan for?

• RPE to choroid

• Accentuates choroidal circulation

What are blue lasers used for?

fluorescein angiography procedures

What are infrared lasers used for?

indocyanine green angiography procedures

What are limitations of Optos?

•Retinal distortion in periphery

•‘Map effect’

•In Optos, the mirror is ellipsoid

•Lash artifact

•Ora serrata not visible – indirect with scleral indentation still needed

What are some clinical uses of optos?

• Peripheral retinal disease and degenerations

• Holes, tears, detachments

• Diabetic retinopathy

• Identifies non-perfusion and neovasc

• Retinopathy of prematurity

• Retinal vein occlusion

• Identifies peripheral retinal ischaemia, neovasc

and macular oedema

• Posterior uveitis

What technique is being used here?

Opto -map