Threshold
Intensity of light that can be perceived 50% of the time and not perceived 50% of the time
Scotoma
Where vision isn’t normal
For a reliable VF, what percentage should the following fall under?
1. Fixation losses
2. False positives
3. False negatives
- Fixation losses - 20%
- False positives - 20%
- False negatives - 33%
What is the MD and clinical impact of False Positives?
Increase MD and delay treatment
What is the MD and clinical impact of False Negatives?
Decrease MD and adds unnecessary treatment
What is the MD and clinical impact of Fixation Losses ?
No impact
Patient returns for follow up. Visual field shows worsening of MD, but fixation losses are at 40%. You think, I’ll bring the patient back in 1-3 months to repeat visual field. What could happen with this patient?
Under treatment
Even thought fixation losses high, VF still shows progression.
If the numeric grid shows a threshold level of ___ at any point, the test is unreliable.
40+
What is the maximum stimulus brightness provided by the perimeter?
0 dB
(The lower the number, the brighter the light)
What are the 6 signs of a ‘Trigger Happy’ patient?
- High FP
- High fixation loss
- High threshold values
- High positive total deviation
- White scotomas on gray scale/no blind spot
- GHT “Abnormally high sensitivity “
What does the MD represent?
Mean Deviation — height of hill of vision compared to age-matched normals
What is the GHT?
Glaucoma Hemifield Test — compares inferior to superior field
What are the possible outcomes for GHT?
- Within normal limits
- Borderline
- Outside normal limits
- Abnormally high sensitivity
- General reduction in sensitivity
Explain why a 10-2 may be useful in EARLY glaucoma
- ~30% of all RGC’s are found in central 8º from fovea
- 24-2 and 30-2 use 6º grid points
- This means the tests miss a lot of potential areas of loss
- 10-2 uses 2º test grids
