DIS - Ocular Imaging II - Week 4 Flashcards
What is an en face image?
A surface scan
Briefly describe how OCT works.
Uses ultrasound, and is based on the concept of different tissue having different refractive indices
List two historical eye scans.
Polarimetry
Scanning laser ophthalmoscopy
List the two forms of OCT and their resolution and depth. Name which is superior.
Time domain - resolution 8um, depth 15um
Spectral domain - resolution 2um, depth 8um
Spectral domain is superior
List the two types of light sources that can be used for OCT. Describe them in terms of their wavelengths.
Standard laser - fixed wavelength OCT
Swept-source OCT - variable wavelength
What does OCT give a reflection of and what is this dependent on?
A reflection or scatter profile that depends on the refractive index of tissue, and correlates well with anatomical features
What kind of depth can a single laser OCT resolve to and can it resolve the choroid?
Fixed depth - usually cannot see the choroid
Describe three advantages of multiple wavelengths during a single sweep in OCT.
Better resolution
Deeper penetration
Faster image acquisition
When using multiple wavelengths in OCT, is there more or less movement artefact and noise?
Less
What are black lines in an OCT scan? Give three examples.
An artefact
-shadows from blood vessels
-shadows from tissue
-echo
Is a whole eye OCT possible?
Yesd
Define ASOCT.
Anterior segment OCT
List four things an ASOCT scan can assess.
Angle and structures
Corneal thickness
Corneal oedema (bullae)
Choroidal swelling
What wavelengths are needed to visualise deeper structures of the eye?
Longer
List the three clinically important structures seen on a retinal OCT scan.
RNFL/GCC
ISe (PR)
RPE/BM
How is photoreceptor integrity judged?
By the presence of ISe
How does the ISe appear on an OCT?
A thin white line
How does the outer segment (OS) appear on an OCT scan?
A thin black line under the ISe and above the RPE
How does the RPE appear on an OCT acan?
A thin white linebelow the black outer segment line
What is the ISe exactly? What elsa is it known as?
The interface between the outer segment and inner segment
Ellipsoid zone
List three appearances of the ISe on an OCT scan indicating a retinal disorder. What does this mean for the photoreceptors?
Thickening
Gaps
Disruptions to the ISe
May indicate local dropout of photoreceptors
What is missing ISe an early sign of?
Photoreceptor (OR) disease
On an OCT scan, what do dark, optically homogenous regions in the retina indicate?
Fluid
How does a choroidal neovascular membrane appear on an OCT scan? Describe the ISe as well (2).
It creates fluid with a thickening and breakup of the overlying ISe