Role of Perimetry in Diagnosing and Managing Glaucoma
Perimetry, particularly automated static threshold perimetry (SAP) with white-on-white stimuli, is the gold standard functional test for diagnosing, monitoring, and managing glaucoma, providing critical information about visual field defects that directly impact patient morbidity and quality of life. 1
Primary Testing Methods
Standard Automated Perimetry (SAP)
- SAP with white-on-white stimuli remains the cornerstone of visual field assessment in glaucoma 1
- Testing strategies can be tailored based on:
- Central threshold sensitivity (24°, 30°, or 10° programs)
- Varying stimulus size
- 10-2 program is particularly useful for detecting early central visual field damage before it becomes evident on wider field tests 1
Alternative Methods
- Goldmann visual fields (manual combined kinetic and static threshold testing) are acceptable alternatives when:
- Patients cannot perform automated perimetry reliably
- Automated perimetry is unavailable 1
- Specialized testing methods:
- Frequency doubling technology - measures contrast sensitivity for frequency doubling stimulus
- Short-wavelength automated perimetry (SWAP) - isolates short-wavelength sensitive cells using blue-light stimulus on yellow background 1
Diagnostic Role
- Helps identify functional vision loss in glaucoma suspects and patients with established glaucoma
- Can detect glaucomatous damage even when structural tests appear normal
- When visual field damage is newly detected, testing should be repeated to confirm changes 1
- Emerging technologies like tablet-based strategies and virtual reality headsets show promise for glaucoma screening and remote monitoring 2
Management Role
Establishing Baseline
- Initial visual field tests establish a baseline for future comparison
- Multiple baseline tests may be needed due to learning effect
Monitoring Progression
- Both trend and event analyses should be used concurrently 3:
- Trend analysis: Provides rates of progression to contextualize disease speed against patient longevity
- Event analysis: Demonstrates "step" changes regardless of timeframe
- Repeating the same testing strategy that showed a new defect is best for confirming visual field changes 1
- Both trend and event analyses should be used concurrently 3:
Treatment Decisions
- Rate and pattern of visual field progression guide treatment intensity
- Central field defects may warrant more aggressive intervention due to greater impact on quality of life
Reliability Considerations
- Visual fields are considered unreliable with:
- Fixation losses >20% (standard) or >33% (flexible criterion)
- False positives or false negatives >33% 4
- To improve reliability:
- Provide clear instructions before testing
- Consider pausing during testing for patients with fatigue or attention difficulties 4
Integration with Structural Testing
- Perimetry should be used in conjunction with structural tests (optic nerve head and retinal nerve fiber layer imaging)
- Structural alterations often precede functional changes detected by perimetry 1
- Computer-based imaging technologies (OCT, confocal scanning laser ophthalmoscopy, scanning laser polarimetry) complement but do not replace perimetry 1
Future Directions
- Artificial intelligence is improving detection and characterization of glaucomatous field damage 2
- Home-based visual field testing may allow for more frequent monitoring 5
- Objective functional tests (like multifocal pattern visually evoked potential) show promise but are not yet ready for widespread adoption 6, 5
Common Pitfalls
- Relying solely on structural tests without functional assessment
- Not repeating visual field tests to confirm new defects
- Failing to consider reliability indices when interpreting results
- Not tailoring the testing strategy to the patient's disease stage (e.g., not using 10-2 programs for central field assessment in advanced cases)
- Overlooking the need for wider testing patterns (24-2 or 30-2) in certain populations, such as patients of Asian descent 4