DIS - Ocular Imaging III - Week 8 Flashcards
What are 5 methods available to image glaucoma?
Drawing
Photography
Scanning laser tomography
Scanning laser polarimetry
Optical coherence tomography
How does a scanning laser tomographer work and how can the focal plane be changed?
A low power laser is scanned in raster fashion over the retina, reflected light is descanned and detected by a photodiode
A small pinhole placed in front of the photodiode can be moved to select the focal plane
How does a scanning laser polarimeter work?
Measures the phase shift of polarised light passing through the eye
-retardation is affected by the arrangement and density of the RNFL
What is variable corneal compensation used for (2) and for what imaging technique?
Used in scanning laser polarimetry
-determines and corrects for each patient’s individual non-RNFL retardation
List 6 analysis results available for the RNFL with scanning laser polarimetry.
Fundus image
RNFL map
Deviation map
TSNIT graph
Parameters/indices
List the two types of OCT available and which is theoretically better and why (2). Compare the diagnostic accuracy of the two.
Time domain
Spectral domain - theoretically better
-spectral domain has high resolution and faster scanning - higher reproducability
Diagnostic accuracy of the two are similar
Which is faster, spectral domain or time domain?
Spectral domain
Can spectral domain give 3D image patterns?
Yes
Where is the loss of cells more easily detected and why?
At the macula because it has the highest concentration of RGCs
What is the minimum distance band and is it better than RNFL thickness in distinguishing glaucomatous eyes from healthy eyes? What technique is it used in?
Spectral domain
Shortest distance between the ILM and bruch’s membrane/RPE termination
MDB is better than RNFL thickness
List three 3D rim parameters and 2D rim parameters each. Which is better?
3D
-minimum distance band
-minimum rim width
-rim volume
2D
-RNFL thickness
-rim area
-rim thickness
3D rim parameters generally outperform 2D
Compare total macular thickness to RNFL thickness for glaucoma diagnosis.
Total macular thickness is worse
List three segmentation macular parameters and their performance (2).
Macular RNFL (mRNFL)
Ganglion cell and inner plexiform layer (GCIPL)
Ganglion cell complex (GCC) - GCC = mRNFL + GCIPL
GCIPL is similar to RNFL and ONH
Minimum GCIPL is the most sensitive parameter
What is an issue with most glaucoma detection studies for diagnosing early glaucoma?
Most detection studies look at discrimination between healthy eyes and established glaucoma
-may not translate to early glaucoma
Which of the following is significantly better than the others for pre-perimetric glaucoma:
RNFL
ONH
Macula
RNFL
Is myopia a risk factor for glaucoma?
Yes
Do structural changes in myopia mimic glaucoma?
Yes
What are thick artefacts seen with myopia due to?
Refractive error and eye length
Can non-glaucomatous eyes be classified as abnormal?
Yes
Compare the macula and RNFL thickness’ ability to detect glaucoma in myopic eyes.
They are similar
Is RNFL thickness diagnostically accurate for detecting glaucoma?
Yes
Compare segmented macular and ONH parameters to RNFL
Comparable, perhaps better
Are there differences in absolute measurements between instruments? Do different instruments have similar diagnostic abilities?
There are differences in absolute measurement
Different instruments have similar diagnostic abilities
Explain the sensitivity and specificity capability of OCT and comment if it is good enough for population screening glaucoma.
They are not high enough to be cost-effective for population screening
What is essential for glaucoma after it is diagnosed and why?
Detecting progression because it will guide treatment
What does progression detection require (3)?
Discrimination between:
-glaucomatous structural damage
-measurement variability
-age related structural loss
Which is more sensitive to RNFL changes, spectral domain or time domain?
Spectral domain
What is compared in event-based progression analysis and when is progression indicated? List one advantage and disadvantage.
Compares a follow-up measurement to a baseline measurement
Advantage - few tests required
Disadvantage - susceptible to outliers
What is compared in event-based progression analysis and when is progression indicated? List two advantages and disadvantages.
Looks at the slope/rate of a line fit through the parameter over time
Progression is indicated when the slope exceeds a threshold
Advantages
-less sensitive to measurement variability
-rate can be used to make a time-to-event prediction
Disadvantages
-large number of tests needed before analysis is reliable
-assumes linear loss
Compare the sensitivity of RNFL, TMT, and GCIPL in detecting glaucoma progression.
All similar
Compare the loss of TMT and RNFL in glaucoma progression groups to stable and undetermined groups.
Rate of TMT loss was greater in glaucoma progression
Rate of RNFL loss was similar
What wavelength does swept-source OCT use and list two advantages of this.
Longer wavelength
-deeper penetration
-faster scan rate
Compare the sensitivity of swept-source OCT for diagnosing pre-perimetric and early glaucoma.
May be more sensitive
What does adaptive optics OCT allow identification of?
Width of nerve fibre bundles
