Automated Perimetry Flashcards
True or False:
The test flash in automated perimetry is a fixed size.
True
What is the most commonly used TF size?
Goldmann III
What about the test flash in VF testing is changed?
The intensity changes in order to determine threshold
When is it appropriate to use a larger stimulus size?
For individuals with poor visual acuity.
In what unit are threshold values expressed in?
Decibels (dB)
What does the threshold value obtained tell us?
How much the TF must be decreased from the max luminance to reach threshold.
If 10dB was obtained for threshold, what does this tell us?
10 dB = 1.0 log unit LESS THAN max luminance.
1.0 log unit = 10x less than 10,000 asb = 1,000 asb
What does a higher dB number tell us?
The higher the dB, the more sensitive the eye is for a given location.
- Less luminance is needed for the patient to detect light
Convert 20dB to asb
20 dB = 2.0 log units = 20x less than 10,000 = 500 asb
What is a fixation loss?
Light is presented in the patient’s blind spot.
- If the patient is fixating where they’re supposed to, they should not be able to see these lights.
- If the patient clicks that they see these lights, that is a fixation loss because they’re not paying attention to where they need to be.
What is considered acceptable for fixation losses?
It is recommended that the fixation losses not exceed 20%
What does a reading of fixation loss greater than or equal to 20% tell us?
The results may not be reliable or the patient may have fixation problems
In ‘graze tracker,’ what do the upward lines reflect?
The deviation from the baseline.
For example, the patient is moving eyes a lot - deviating from the baseline (central light).
In ‘gaze tracker,’ what do the downward lines indicate?
An inability to make a measurement (e.g., a blink).
What is a false positive?
Signifies that the patient pushes the button before the stimulus is presented; they are “trigger happy.”
At does a reading of greater than 15% false positives tell us?
That the data is unreliable
True or False:
False positives are one of the most important and useful reliability indices.
True!
It’s a way to show the subject’s engagement; it’s not a fixation problem, rather, they’re not waiting to see the target.
What are false negatives?
When the patient misses a stimulus that is brighter than one that was seen previously.
For example, the subject clicks the button for a the first few trials stating they detect a light level. When a higher illuminance is presented, the patient does not click. They should see it because they responded for lower luminance.
For a sensitivity plot/numeric plot, what unit are the values in?
Threshold values in decibels (dB)
In a sensitivity/numeric plot, what does a dB reading signify?
How much the TF must be decreased from the max luminance to reach threshold.
What is a normal threshold for a young observer in a sensitivity/numeric plot?
38-40 dB.
Which plot is the basis for 5 other plots included in the VF printout?
The sensitivity/numeric plot.
What is the relationship between threshold and sensitivity?
The lower the threshold (i.e., the less luminance needed for the patient to detect the light), the greater the sensitivity.
What does the total deviation plot convey?
The difference in decibels between the patient’s results and the averaged age-corrected normal values at each point in the visual field.
