DIS - Glaucoma Assessment Tutorial II - Week 5 Flashcards
What is better at discriminating glaucoma suspects from glaucoma patients, OCT or stero photos?
OCT
Is it common or rare to find simultaneous defects in both structures and function at diagnosis?
Rare
What is the issue of correpating structure and function of the ganglion cells? Describe in terms of VF sensitivity.
The variability in ganglion cell density as we move away from the fovea
How much does a 3dB point reduction in VF sensitivity correlate with the number of ganglion cells outside the macula and the perifovea?
10 ganglion cells outside the macula
230 ganglion cells in the perifovea
Once a field defect is present, is progression better detected by VF changes or disc changes?
VF changes
Comparing structure vs function (VF), which is better at detecting early glaucoma? what about more advanced glaucoma?
Structure better at detecting early glaucoma
VFs better for advanced glaucoma
Comparing OCT vs function (VF), which is better at detecting early glaucoma? what about more advanced glaucoma? Keeping this in mind, what is the danger of using only one of these techniques (ie. OCT because its quicker)?
OCT better at detecting early glaucoma
VFs better for advanced glaucoma
-significant number of cases missed by either of the above alone
-dont be tempted to use only one technique
How many test points does the 30-2 have? Give one advantage and two disadvantages.
76
Advantage - more points in the temporal field
Disadvantage - longer test time, variable threshold of outer ring of points
How many test points does the 24-2 have? Give three advantages.
54
Advantages
-still tests out to 30 degrees in the nasal step region
-quicker test time
minimises outer ring variability
How many test points does the 10-2 have? Is there strong or weak evidence of central defects early in the disease process? What is this VF setup used to assess? What is its test time like?
68 (in the central 10 degrees)
Strong evidence of central defects early in the diease process
Used to quantify any defects of central 4 points on 24-2 or 30-2
Much longer test time
What does the evidence comparing 30-2 and 24-2 suggest in terms of best compromise for speed, comfort, and reliable data?
24-2 in most cases gives the best compromise while being comparable to 30-2
Consider the visual field area tested by 10-2. What quadrants are affected first in glaucoma (2)?
Inferotemporal and superotemporal
When is the temporal disc often affected in glaucoma? What about the nasal quadrant of the disc?
Not until later in the disease
The nasal quadrant is last
True or false
Central VF defects are due to damage to the temporal papillomacula bundle
If true, explain why.
If false, explain what the defect is due to.
False
It is due to damage at the junction of the inferior-temporal quadrants
On average, by how many degrees is the ONH higher than the fovea, and how does this affect nerve fibres synpasing from the disc to the fovea (which quadrant specifically)?
On average 5 degrees higher than the fovea
This means nerve fibres synapse from the inferotemporal disc to the fovea
What two defects does damage to the inferotemporal quadrant reigon of the disc lead to and in what degree of the visual field?
Leads to superonasal steps and arcuate defects within the central 10 degree visual field
If the fovea-disc angle is larger, what is more likely?
Parafoveal VF defects
List an advantage and disadvantage of SITA standard for VFs.
Advantage - greater number of thresholding steps - more precise
Disadvantage - longer testing time
List an advantage and disadvantage of SITA fast for VFs.
Advantage - quicker testing time
Disadvantage - slightly less precise
What do studies comparing SITA standard to SITA fast suggest?
While SITA standard is more precise, it is unlikely to make a difference to improve the time to detect VF progression
How much faster is SITA fast vs SITA standard?
50% faster
Does SITA fast require a new baseline if switching over from SITA standard?
No
Are SITA fast and SITA standard interchangeable?
Yese
List four types of defects typical of early glaucoma.
Nasal step
Paracentral scotoma
Arcuate defect
Temporal wedge
Are defects more likely to be found in the superior or inferiord hemifield? By how many times?
2-5 times more likely for visual field defects to be located in the superior hemifield
What percentage of glaucoma patients in both eyes had defects in only the infeiror hemifield?
Less than 10%
Are visual fields subjective or objective? Is it very variable?
Subjective
Very variable
List three reliability indicators for visual fields and describe them in terms of their effect on reliability.
Fixation losses - may be acceptable
False positives - always bad
False negatives - least worrisome
In what three ways can fixation losses be evaluated? Explain each. Note which is the least effective.
Blind spot monitor
-ONH location mapped early
-if patient shifts/tilts head, fixation losses are flagged
Video monitor
-requires practitioner attention
-least effective
Gaze tracker
-relies on a good corneal reflex, doesnt always work
Define mean deviation for visual fields. How is it grouped, and what is the measurement range?
Overall depression of visual fields compared to age-matched normals
Grouped in decades
0dB to -35dB
List three things that can affect mean deviation.
Media opacity
Small pupils
Uncorrected refractive error
Define point standard deviation and what it highlights.
Point variance from the patient’s own hill of visiond
Highlights areas of scotoma more depressed than the mean deviation
What is the visual field index, what data does it use (2), and is it easily comprehended by patients?
A global index that assigns a number between 1% and 100% based on an aggregate percentage of visual, function with 100% being a perfect age-adjusted visual field
Uses data from mean deviation and point standard deviation
Easily comprehended by patients
Is visual field index affected by cataract/media opacities?
No
What is a glaucoma hemifield test?
Cluster comparison between superior and inferior hemifields
What is the most common grading system for grading the severity of glaucomatous VF defects? What is it based on and what does it represent? What has it recently begun utilising and why?
Glaucoma staging system
Based on mean deviation
-overall reduction in sensitivity
Recently utilises visual field index
-to eliminate effect of cataract on progression analysis
Describe the three stages of the glaucoma staging system in terms of mean deviation and VFI cutoffs.
Mild
-MD 0 to -6dB
-VFI 100 to 80%
Moderate
-MD -6 to -12dB
-VFI 80 to 60%
Severe
-MD worse than -12dB
-VFI <60%
True or false
VF defect within 5 degrees of fixation at any level of mean deviation is considered to be severe glaucoma
True
Is it easy or difficult to differentiate random VF losses from true early glaucoma?
Very difficult
If a defect is found, what needs to be shown and how long later?
Needs to be repeatable 2-4 weeks later
Ideally, how many tests in a row should a defect be present?
3
Do significant defects tend to occur in clusers or individual points?
Clusters
Is mean deviation good for early detection of glaucoma? Explain why.
Not good
Averages all points, missing earlyy shallow defects
Is VF testing varialbe from visit to visit?
Yes
What is needed for a baseline for VF testing when starting glaucoma assessmentd? Explain why it needs to be so.
Need 2 or 3 VF tests close together to establish a baseline and determine the patients variability in taking the test
Needs to be close together so that nay variations are due to the patient’s performance, not glaucoma progression
What is considered true deterioration for VF (2)? What does assessing this require?
When the change over time is worse than the natural deterioration of VF with age and the patient’s own inherent variability
Requires guided progression analysis
What are two methods of detecting progression using guided progression analysis?
Event analysis
Trend analysis
What does an event analysis do? What three things does it detect? What is it based on? What does it flag?
Looks for change in each point of the VF
-deepening of an existing scotoma
-widening of an existing scotoma
-new scotoma in a different part of the field
It is based on pattern deviation plot, not mean deviation
Flags points that have changed more than the patient’s inherent variability
What is the minimum number of VF exams needed for an event analysis? Describe them.
3
2 baselines, one followup
What does event analysis tell us? What does it not tell us?
If progression has occured, not how quickly
What does trend analysis look for? What does it use (2)? Is it quicker or slower than event analysis?
Looks for progression over the entirety of the visual field, not each point
Uses global data from mean deviation or visual field index
Takes longer to statistically detect progression than event analysis
What is the minimum number of VF exams needed for a trend analysis?
5 - 6 VF exams
What does trend analysis reveal (2) and what does it not tell us?
Reveals occurence of progression and rate of progression
Doesnt tell us which part of the VF is worsening (event analysis tells us this)
What can trend analysis calculate?
Rate of progression to predict future VF loss
-calculates time taken to progress to blindness
How is rate of progression measured in trend analysis?
dB/year of MD loss or %/year VFI loss
What is the average rate of loss?
-0.06dB/year (virtually no progression)
What is considered slow progression? What about rapid? What about catastrophic? What percentage of glaucoma patients fall into each category?
Slow - less than -1.0dB/year (95%)
Rapid - more than -1.0dB/year (4.3%)
Catastrophic - more than -2.0dB/year (1.5%)
Do all patients progress at the same rate?
No
What percentage of untreated glaucoma patients did not progress over 5 years, if any?
38%
What percentage of untreated normal tension glaucoma patients did not progress over 7 years, if any?
50%
How often should VFs be taken for a newly diagnosed glaucoma patient? What does this allow for? Does it matter when they are done? Explain.
6 tests in the first two years
Allows for progression rate to be determined
Compared with 4 month and 6 monthly VF tests evenly spaced over 2 years, clustered VF testing (3 at t=0, 3 at t=2) is more sensitive with fewer false positives
What is the aim when considering the frequency of VF testing?
To find patients progressing more than -1.0dB/year
-most likely to progress to blindness
Is a rapid VF test done frequently more valuable than a longer, more precise test done infrequently?
Yes
What is required for a definitive diagnosis of glaucoma? Explain.
3 structural signs of glaucoma that all match each other
No need to have a VF defect for diagnosis
