Visual Field Testing in Glaucoma

Visual Field Testing in Glaucoma - VFT Basics: Unveiling Loss

• Visual Field (VF): Area visible to one eye with fixed gaze; "Hill of Vision" concept.
• Glaucoma causes progressive, irreversible VF loss due to optic nerve damage.
• VFT detects defects early, often before symptoms, and monitors progression.
• Sensitivity measured in decibels (dB); higher dB = better light sensitivity. Normal peak ~35 dB.
• Defects: Nasal step, paracentral scotoma, arcuate (Bjerrum's) scotoma.

⭐ Bjerrum's (arcuate) scotoma, arching from blind spot, is a hallmark of early glaucoma.

Visual Field Testing in Glaucoma - Perimetry Types: Test Tactics

• Standard Automated Perimetry (SAP): Gold standard (e.g., Humphrey, Octopus).
  • Stimulus: White, Size III. Background: White.
  • Test Strategies:
    • Threshold: SITA (Standard, Fast, Faster) - common, efficient. Full Threshold - longest, most data.
    • Suprathreshold: Rapid screening; less detail.
• Frequency Doubling Technology (FDT): Targets magnocellular (M-cell) pathway; rapid screening.
• Short Wavelength Automated Perimetry (SWAP): Blue stimulus (Size V) on yellow background; detects early blue-yellow defects. Higher variability.
• Reliability Indices (SAP):
  • Fixation Losses: < 20%
  • False Positives: < 15%
  • False Negatives: < 15%

⭐ SITA strategies significantly reduce test duration compared to Full Threshold, enhancing patient cooperation and test reliability.

Visual Field Testing in Glaucoma - Defect Patterns: Glaucoma's Footprints

• Early Defects (Reflect RNFL Damage):
  • Paracentral scotoma: In Bjerrum's area (10-20° from fixation).
  • Nasal step (Rønne's): Respects horizontal meridian.
  • Seidel's scotoma: Sickle-shaped extension from blind spot.
  • Temporal wedge defect: Less common.
• Progressive Defects:
  • Arcuate scotoma (Bjerrum scotoma): Arch-shaped, from blind spot to nasal field; coalescence of smaller scotomas.
  • Ring scotoma (Double arcuate): Encircles fixation.
• Advanced Defects:
  • Central and/or temporal island of vision.
• End Stage:
  • Minimal remaining vision or No Light Perception (NLP).

⭐ The nasal step is a classic early glaucomatous defect, often appearing before significant changes in visual acuity.

Visual Field Testing in Glaucoma - Report Analysis: Decoding Dots

• Reliability Check (Key for valid interpretation):
  • Fixation Losses (FL): < 20%
  • False Positives (FP): < 15%
  • False Negatives (FN): < 15%
• Interpreting Dots & Global Indices:
  • Dots: Represent retinal sensitivity in decibels (dB). Lower dB = ↓ sensitivity.
  • Mean Deviation (MD): Overall field depression. More negative = worse. ↓ in glaucoma.
  • Pattern Standard Deviation (PSD): Localized loss. ↑ in glaucoma.
  • Visual Field Index (VFI): 0-100%; estimates percentage of remaining vision.
• Key Plots: Grayscale, Total Deviation, Pattern Deviation (highlights focal defects), Glaucoma Hemifield Test (GHT) (compares hemifields).

⭐ Visual Field Index (VFI) is a key staging parameter, expressed as a percentage (0-100%), and correlates well with retinal ganglion cell (RGC) count, reflecting structural damage an_function_call_response

High‑Yield Points - ⚡ Biggest Takeaways

• SAP (Standard Automated Perimetry) is the gold standard for assessing glaucomatous field loss.
• Early defects: Paracentral scotoma, nasal step (Rønne's), Bjerrum's scotoma (arcuate).
• Seidel's scotoma: Sickle-shaped extension of the blind spot, an early sign.
• Progression patterns: Arcuate scotoma can enlarge to a ring scotoma or nasal breakthrough.
• Advanced loss: Only a central island and temporal island of vision remain.
• Key HFA indices: VFI (Visual Field Index) for staging/progression, GHT (Glaucoma Hemifield Test) for classification of results based on normative data.