3. VF Testing patterns and strategies

What is the purpose of the threshold kinetic strategy in perimetry?

• Maps the outline of the visual field or defect shape

• Determines where a moving stimulus goes from not seen → seen (threshold point)

• Results are displayed as isopters (contour lines of equal sensitivity)

How does kinetic perimetry differ from static perimetry?

• Kinetic: moving stimulus → finds boundary of vision (isopter)

• Static: fixed stimulus → finds threshold sensitivity at specific points

How is threshold determined in kinetic perimetry?

• Stimulus of fixed intensity is moved from non-seeing → seeing area

• Threshold = location where patient first detects stimulus

What instruments are commonly used for kinetic perimetry?

• Tangent screen

• Arc perimeter

• Goldmann perimeter

• Some automated: Octopus 900, HFA3

What are the advantages of kinetic perimetry?

• Quickly maps peripheral visual field extent

• Excellent for visual field shape and large defects

• Faster than full static threshold testing in some cases

In what clinical situations is kinetic perimetry particularly useful?

• Peripheral field screening / mapping extent

• Driving eligibility testing

• Post-stroke visual field evaluation

• Disability determination

• Severe field loss (e.g., retinitis pigmentosa)

• Patients unable to perform static testing (e.g., children)

Why is kinetic perimetry used less frequently than static automated perimetry?

• Static testing provides:

  • Quantitative threshold data (dB)

  • Better disease monitoring (e.g., glaucoma)

• Kinetic mainly gives qualitative boundary information

How are results from kinetic perimetry displayed and interpreted?

• Isopters = lines connecting points of equal sensitivity

• Defects appear as:

  • Constricted fields

  • Scotomas within isopters

How do kinetic and static perimetry complement each other clinically?

• Kinetic: defines extent and shape of field loss

• Static: quantifies depth/sensitivity loss (dB)

• Together → complete understanding of visual field defects

What are the main screening strategies used in visual field testing?

• Single intensity strategy

• Threshold-related strategy (qualitative)

• 3-zone strategy

• Quantify defects strategy

What defines a threshold-related screening strategy?

• Records only “seen (hit)” vs “not seen (miss)”

• Provides qualitative results only

• Does NOT quantify defect depth

How does the 3-zone strategy classify visual field defects?

Uses different symbols/zones:

• Normal (no defect)

• Relative defect

• Absolute defect

What happens in the quantify defects strategy?

• Points missed on screening are followed up with threshold testing

• Converts screening → quantitative data (dB values)

How does the threshold-related screening test proceed at each point?

• Start at ~6 dB brighter than expected threshold

• If seen → recorded as seen (no retesting)

• If missed → retested

  • Seen on repeat → recorded as seen

  • Missed again → recorded as missed

Why does threshold-related screening start ~6 dB above expected threshold?

• Designed so ~95% of normal population will see it

• Efficiently identifies abnormal points

What is the next step when defects are detected on screening visual fields?

• Do NOT repeat screening

• Proceed to a full threshold test

What findings on screening warrant a threshold visual field test?

• ≥2 adjacent missed points

• ≥1 missed point within 20° of fixation

• Central sensitivity ≤26 dB (reduced hill of vision)

What are the key stimulus parameters in Humphrey threshold perimetry?

• Duration: ~200 ms

• Size: usually Goldmann size III (standard)

• Intensity: varied to determine threshold

Why is Goldmann size III the standard stimulus in automated perimetry?

• Provides best balance of:

  • Sensitivity to defects

  • Test reproducibility

• Used almost exclusively in Humphrey testing

What are the two components you must choose for Humphrey testing?

• Pattern (e.g., 24-2, 10-2, G, M)

• Strategy/algorithm (e.g., SITA Fast, SITA Standard, TOP)

What are the most commonly used Humphrey visual field patterns?

• 24-2 → most commonly used

• 30-2 → wider field

• 10-2 → central field

How do 24-2 and 30-2 compare?

• 24-2:

  • Fewer points

  • Faster

  • Captures most clinically useful info

• 30-2:

  • Wider (to 30°)

  • More points but less commonly used

What is the advantage of the 24-2C pattern?

• Adds extra central (macular) points

• Improves detection of early central defects

When is the 10-2 test pattern used?

• Macular disease

• Small central scotomas

• High-density testing within central 10°

What is the G pattern and when is it used?

• Central 30° pattern based on nerve fiber layer anatomy

• Optimized for glaucoma detection

What is the M pattern in perimetry?

• Similar to 10-2, but with greater emphasis near fovea

• Designed for macular assessment

What is the difference between a pattern and a strategy in perimetry?

• Pattern = spatial layout of test points

• Strategy = algorithm used to determine thresholds

Why is the 24-2C pattern preferred over standard 24-2 in some cases?

• Better detects early glaucomatous damage near fixation

• Samples areas along nerve fiber bundles

How does the staircase procedure determine threshold in static perimetry?

• Start at a given intensity

• Adjust brightness based on response:

  • Seen → go dimmer

  • Not seen → go brighter

• Continue until threshold is found

What are the step sizes used in the Humphrey staircase strategy?

• 4 dB steps → coarse search (faster)

• 2 dB steps → fine thresholding (more precise)

What happens to stimulus intensity based on patient response in threshold testing?

• Seen → decrease intensity (dim by 4 dB or 2 dB)

• Not seen → increase intensity (brighten by 2 dB)

What was the original Humphrey threshold algorithm and how did it work?

• Humphrey Full Threshold (1980s)

• Used staircase method:

  • 4 dB steps → coarse search

  • 2 dB steps → fine thresholding

• Similar to Octopus “Normal” strategy

What is SITA and why was it developed?

• SITA = Swedish Interactive Thresholding Algorithm (1990s)

• Reduces test time without losing accuracy

• Uses prior data + probability models

How does SITA determine thresholds more efficiently?

• Starts near expected threshold (uses age norms)

• Uses maximum likelihood/statistical modeling

• Adjusts pacing based on reaction time

• Stops when uncertainty is low enough

• Recalculates thresholds using neighboring points + consistency

What defines SITA Standard?

• Uses:

  • Maximum likelihood model

  • 4 dB → 2 dB staircase

• Balance of accuracy + time

• Most accepted for follow-up/monitoring

How does SITA Fast (and Faster) differ from SITA Standard?

• Uses mostly 4 dB steps (less refinement)

• ~2/3 the time of SITA Standard

• Slightly ↓ test-retest reliability

What is a common modern testing combo for Humphrey?

24-2C + SITA Faster

What determines when SITA stops testing at a point?

• When uncertainty (confidence interval) is sufficiently low

• Based on:

  • Patient responses

  • Nearby points

  • Reaction time

How do staircase and SITA approaches relate?

Full Threshold: pure staircase (4 dB → 2 dB)

SITA: modified staircase + statistical prediction

Both aim to find threshold sensitivity, but SITA is adaptive and faster

What is the key trade-off when choosing a perimetry testing strategy?

• Time vs accuracy (resolution)

• Faster strategies →

  • ↓ test time

  • ↓ spatial resolution/detail (defects look smoother, shallower)

How do fast strategies (TOP / SITA Fast) affect how defects appear?

• Defects appear:

  • Shallower

  • Smoother edges

• May miss:

  • Small or isolated defects

What is the main limitation of TOP / SITA Fast strategies?

Decreased ability to detect:

• Subtle threshold changes

• Small focal defects

In which patients are SITA Fast / TOP particularly useful?

• Young patients

• Good test takers

• Fatigued patients

• When short test time is needed

What is the current recommendation regarding SITA Faster?

• SITA Fast / SITA Faster now recommended for most patients

• Benefits (speed + compliance) outweigh small loss in reliability

What is the practical equivalence between Humphrey and Octopus strategies?

• SITA Standard ≈ Dynamic

• SITA Fast / Faster ≈ TOP

• Full Threshold ≈ Normal

What are common perimetry setups used in clinic?

• Octopus:

  • 24-2 TOP

• Humphrey (HFA):

  • 24-2 SITA Fast

  • OR 24-2C SITA Faster