DIS - Ocular Imaging III - Week 8

Question 1

What are 5 methods available to image glaucoma?

Answer 1

Drawing
Photography
Scanning laser tomography
Scanning laser polarimetry
Optical coherence tomography

Question 2

How does a scanning laser tomographer work and how can the focal plane be changed?

Answer 2

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

Question 3

How does a scanning laser polarimeter work?

Answer 3

Measures the phase shift of polarised light passing through the eye
-retardation is affected by the arrangement and density of the RNFL

Question 4

What is variable corneal compensation used for (2) and for what imaging technique?

Answer 4

Used in scanning laser polarimetry
-determines and corrects for each patient’s individual non-RNFL retardation

Question 5

List 6 analysis results available for the RNFL with scanning laser polarimetry.

Answer 5

Fundus image
RNFL map
Deviation map
TSNIT graph
Parameters/indices

Question 6

List the two types of OCT available and which is theoretically better and why (2). Compare the diagnostic accuracy of the two.

Answer 6

Time domain
Spectral domain - theoretically better
-spectral domain has high resolution and faster scanning - higher reproducability
Diagnostic accuracy of the two are similar

Question 7

Which is faster, spectral domain or time domain?

Answer 7

Spectral domain

Question 8

Can spectral domain give 3D image patterns?

Answer 8

Yes

Question 9

Where is the loss of cells more easily detected and why?

Answer 9

At the macula because it has the highest concentration of RGCs

Question 10

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?

Answer 10

Spectral domain
Shortest distance between the ILM and bruch’s membrane/RPE termination
MDB is better than RNFL thickness

Question 11

List three 3D rim parameters and 2D rim parameters each. Which is better?

Answer 11

3D
-minimum distance band
-minimum rim width
-rim volume
2D
-RNFL thickness
-rim area
-rim thickness

3D rim parameters generally outperform 2D

Question 12

Compare total macular thickness to RNFL thickness for glaucoma diagnosis.

Answer 12

Total macular thickness is worse

Question 13

List three segmentation macular parameters and their performance (2).

Answer 13

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

Question 14

What is an issue with most glaucoma detection studies for diagnosing early glaucoma?

Answer 14

Most detection studies look at discrimination between healthy eyes and established glaucoma
-may not translate to early glaucoma

Question 15

Which of the following is significantly better than the others for pre-perimetric glaucoma:
RNFL
ONH
Macula

Answer 15

RNFL

Question 16

Is myopia a risk factor for glaucoma?

Answer 16

Yes

Question 17

Do structural changes in myopia mimic glaucoma?

Answer 17

Yes

Question 18

What are thick artefacts seen with myopia due to?

Answer 18

Refractive error and eye length

Question 19

Can non-glaucomatous eyes be classified as abnormal?

Answer 19

Yes

Question 20

Compare the macula and RNFL thickness’ ability to detect glaucoma in myopic eyes.

Answer 20

They are similar

Question 21

Is RNFL thickness diagnostically accurate for detecting glaucoma?

Answer 21

Yes

Question 22

Compare segmented macular and ONH parameters to RNFL

Answer 22

Comparable, perhaps better

Question 23

Are there differences in absolute measurements between instruments? Do different instruments have similar diagnostic abilities?

Answer 23

There are differences in absolute measurement
Different instruments have similar diagnostic abilities

Question 24

Explain the sensitivity and specificity capability of OCT and comment if it is good enough for population screening glaucoma.

Answer 24

They are not high enough to be cost-effective for population screening

Question 25

What is essential for glaucoma after it is diagnosed and why?

Answer 25

Detecting progression because it will guide treatment

Question 26

What does progression detection require (3)?

Answer 26

Discrimination between:
-glaucomatous structural damage
-measurement variability
-age related structural loss

Question 27

Which is more sensitive to RNFL changes, spectral domain or time domain?

Answer 27

Spectral domain

Question 28

What is compared in event-based progression analysis and when is progression indicated? List one advantage and disadvantage.

Answer 28

Compares a follow-up measurement to a baseline measurement
Advantage - few tests required
Disadvantage - susceptible to outliers

Question 29

What is compared in event-based progression analysis and when is progression indicated? List two advantages and disadvantages.

Answer 29

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

Question 30

Compare the sensitivity of RNFL, TMT, and GCIPL in detecting glaucoma progression.

Answer 30

All similar

Question 31

Compare the loss of TMT and RNFL in glaucoma progression groups to stable and undetermined groups.

Answer 31

Rate of TMT loss was greater in glaucoma progression
Rate of RNFL loss was similar

Question 32

What wavelength does swept-source OCT use and list two advantages of this.

Answer 32

Longer wavelength
-deeper penetration
-faster scan rate

Question 33

Compare the sensitivity of swept-source OCT for diagnosing pre-perimetric and early glaucoma.

Answer 33

May be more sensitive

Question 34

What does adaptive optics OCT allow identification of?

Answer 34

Width of nerve fibre bundles