Lecture 4: Automated perimetry Flashcards
What is manual perimetry?
What are the negatives?
What are the different types of perimetry?
-kinetic visual fields (Goldman)
-difficult to measure and poor reproducibility
kinetic: moving target
static: stationary target. threshold or supra-threshold
What are the features of the humphrey field analyser?
*Gold standard
*Full threshold perimetry
*Commonly found in hospitals
*Not used in some countries (France, Germany), octopus used instead
*It’s a projection bowl perimeter
*31.5asb background luminance
What is the size of the blindspot in Goldmanns and HFA?
Goldmanns: 5 degrees horizontally and 7 degrees vertically
HFA: 5 degrees horizontally
What are the normal values for retinal sensitivity in decibels?
33dB
if 0dB: brightest stimulus is shown, absolute defect
What are the benefits of the new HVFA II?
What types of full threshold testing can you get?
*Good compact design
*User friendly
*Gaze tracker
*Smart data acquisition (SITA)
*Central 30-2
-30 degrees testing
-76 points
(2 stands for amount of reversals whilst measuring threshold)
*Central 24-2
-24 degrees
-more common due to shorter test time
-54 test points
-90% of initial gluacotmous field defects in this 24 degrees area.
-the standard 24-2 visual field neglects 80% of a person’s visual field
What is the threshold?
How is it measured?
the level of stimulus a person can see at each location in the visual field
*Machine spends more time measuring threshold at 4 points known as primary/seed points
*4 locations, 1 in each quadrant of the visual field
*These 4 points are used a predictor of what would happen in the rest of the field
What is the staircase procedure?
What is the measured threshold?
-1st stimulus is presented at a brighter level than what a person is likely to see
-Machine has an aged, matched value for everyone visual field at each location.
-When px sees this stimulus, machine reduces intensity (makes it dimmer), by 4 dB
-If px sees stimulus again it goes down another 4dB. If Px cant see it. This is 1st reversal.
-If px cant see: Stimulus gets brighter by 2dB
Second reversal: when stimulus is seen again
difference between last unseen point and the 2nd reversal
What are the advantages and disadvantages of threshold testing?
-Stimulus parameters standardised & can be varied
-Examination strategy is known & reproducible
-No observer bias
-Computer records
-Examination delegated to non-qualified staff
*Noise: variability:
-pupil size
-media opacity (cataract)
-Response reliability
-poor fixation
-ptosis
-Px not blinking
-Lens rim
-Refraction
-Lid/brow
*Learning effects-performance improves after doing more tests. May have to disregard earlier test
*Fatigue effects-can cause reduction in sensitivity and noise increases. More apparent in tests longer than 10 minutes. Minimised by rest periods between tests and quicker tests (SITA).
What is SITA testing?
*Swedish interactive testing algorithm
*The new gold standard for testing
*Based on data from normal and glaucomatous people
*Uses previous responses
*Results from neighbouring test points used
*Presents more stimuli near threshold
What are the advantages and disadvantages of SITA testing?
*Faster than traditional methods. Intelligent testing
*Less fatigue and preferred by patients
*Black box method
*SITA fast is even quicker, usually larger step size in staircase (useful for follow up)
*Some research indicates SITA fast may be less accurate than SITA standard. Can increase variability
What is short-term fluctuation (SF)?
How is it measured?
What are the disadvantages?
*Measure of variance/SD (standard deviation)
*Uses 10 repeat values (measures at the start and end of test)
*If the response to these points is the same, then variance/SD is 0
*If there are large differences, then variance/SD is large
-the larger the VF damage, the more variability
*Disadvantages: increases test time, 10 points can’t be representative
What technique is used for blind spot monitoring?
What are the disadvantages?
*Heijl-Krakau technique: maps BS at start of test.
*If BS presentation seen (light in presented in BS area and px responds), then assume loss of fixation
*This is done a number of times (trials) with % seen an estimate of FL
-incorrect location of BS
*BS is large area
*Time consuming
*Sampling-how many times are you going to test it
*Poor precision
What does SITA use to measure fixation loss?
What are the disadvantages?
*SITA can turn off heijl-Krakau technique
*Can use eye movement recorder instead:
-Manhattan plot
-optical tracking device
Should look smooth
problems with small pupils
doesn’t monitor head movement
What are false positives?
What are catch trials?
How are false positives measured in SITA testing?
*No stimulus but px presses button. Can be guessing
*Catch trials: projector moves slightly, excepting stimulus but stimulus not shown.
*FP rate estimated by analysis of response times
*No extra testing
*Uses a listening window: expected to press the button. If response is always in what’s expected, then px is consistent.
-FP is more reliable indicator of reliability than FN
How are false negatives measured?
What are the disadvantages?
*Once threshold is established at these points, machine goes back to these points. Machines shows a point 9dB above the threshold and they DONT press the button, you know they have lost attention
*Most unreliable information on visual field sheet
*Disadvantages: dependant on extent of VF loss, small samples so imprecise
