How do I interpret a visual field (perimetry) report?

How to Interpret a Visual Field (Perimetry) Report

Start by assessing reliability indices, then systematically evaluate the pattern deviation plot for characteristic defect patterns, correlate findings with the total and pattern deviation probability maps, and finally integrate these results with clinical examination and imaging findings.

Step 1: Assess Test Reliability

Before interpreting any visual field, verify the test quality by examining reliability indices 1:

• Fixation losses: Should be <20% (indicates patient maintained steady gaze)
• False positives: Should be <15% (patient didn't respond when no stimulus presented)
• False negatives: Should be <33% (patient responded to dimmer stimuli but missed brighter ones)
• Unreliable tests require repeat testing before making treatment decisions 1

Step 2: Identify the Pattern of Visual Field Loss

The American Academy of Ophthalmology defines specific patterns that guide diagnosis 1, 2:

Glaucomatous Defects (Do NOT Respect Vertical Midline)

• Arcuate scotomas: Nerve fiber bundle defects following the arcuate pattern of retinal nerve fibers 1, 2
• Nasal steps: Defects that cross the vertical meridian 1, 2
• Paracentral depressions: Clusters of depressed test points 1
• Loss respecting the horizontal midline: Greater loss in one hemifield versus the opposite hemifield in early/moderate cases 1

Neurological Defects (Respect Vertical Midline)

• Homonymous hemianopsia: Loss in the same half of both visual fields (right or left), indicating chiasmal or post-chiasmal damage 1, 2
• Bitemporal hemianopsia: Loss in temporal fields of both eyes, suggesting chiasmal lesion 1
• Quadrantanopia: Loss in one quadrant respecting both horizontal and vertical meridians 1

Step 3: Evaluate the Grayscale and Numerical Plots

Automated static threshold perimetry (SAP) with white-on-white stimuli is the gold standard 1:

• Grayscale plot: Provides visual representation of sensitivity across the field
• Numerical values: Show threshold sensitivity in decibels (dB) at each test location
• Normal values: Typically 30-35 dB in central field, decreasing peripherally 1

Step 4: Analyze the Pattern Deviation and Total Deviation Maps

• Total deviation: Compares patient's results to age-matched normal database 1
• Pattern deviation: Corrects for overall depression (cataracts, media opacity), highlighting localized defects 1
• Probability symbols: Black squares indicate statistically significant depression (p<0.5% most abnormal) 1

Step 5: Assess Global Indices

• Mean deviation (MD): Overall field depression; negative values indicate loss 1
• Pattern standard deviation (PSD): Measures irregularity; elevated in localized defects 1
• Visual field index (VFI): Percentage of normal field remaining, weighted toward central vision 1

Step 6: Determine Severity of Glaucomatous Damage

The American Academy of Ophthalmology categorizes severity as 1:

• Mild: Normal visual field with optic nerve/RNFL abnormalities
• Moderate: Visual field abnormalities in one hemifield not within 5 degrees of fixation
• Severe: Visual field abnormalities in both hemifields and/or loss within 5 degrees of fixation

Step 7: Confirm New Defects

Before changing treatment, repeat visual field examinations are required for unreliable results or new glaucomatous defects 1. Use the same testing strategy for confirming progression 1.

Common Pitfalls to Avoid

• Don't interpret unreliable fields: High false positives/negatives invalidate results 1
• Don't ignore the pattern deviation: Total deviation may show diffuse depression from cataracts, while pattern deviation reveals true localized defects 1
• Don't diagnose progression on single test: Requires confirmatory testing 1
• Don't use 24-2 or 30-2 alone for advanced disease: Central 10-2 testing is needed when loss approaches fixation (only 4 points sample central 10 degrees on standard testing) 1

Alternative Testing Methods

When standard automated perimetry cannot be performed reliably 1:

• Goldmann perimetry: Manual kinetic and static threshold testing is acceptable alternative 1
• Frequency doubling technology: Helpful for detecting early glaucomatous damage 1
• Short-wavelength automated perimetry (SWAP): May detect early damage before standard perimetry 1