How to Read Your Visual Field Report

A visual field test report uses numbers, gray-scale shading, probability maps, and reliability measures to show which parts of the visual field are working. The examples below use a Humphrey 24-2 report; similar principles apply to Octopus and other perimeters.

What a Visual Field Test Measures

A visual field test measures how sensitive each part of your visual field is - how dim a light you can detect at each location while your eye stays fixed on a central target. The result is a map of light sensitivity across the entire visual area of one eye at a time.

The report shows that map in several different views, each highlighting different aspects of the data. The same data appears in each view, just transformed differently for clinical interpretation.

A Tour of a Humphrey 24-2 Report

A typical Humphrey 24-2 single-field analysis printout has six main sections. Working through them in order:

1. Patient and Test Information (Top of Page)

• Name, date of birth, eye tested
• Date and time of the test
• The test pattern (e.g., 24-2) and strategy (e.g., SITA-Standard, SITA-Faster)
• Pupil size, refractive correction used during the test

The strategy matters: SITA-Standard is the historical default, SITA-Faster is shorter (and increasingly common). Comparing tests across different strategies can be misleading.

2. Reliability Indices (Top Right)

These tell you whether the patient was paying attention and reliably reporting what they saw:

• Fixation losses - how often the patient looked away from the central target during the test. Around 20% or higher is commonly flagged and needs clinical judgment
• False positive errors - how often the patient pressed the button when no light was shown. High false positives, especially around 15% or higher on many modern Humphrey strategies, may overstate visual function
• False negative errors - how often the patient missed a light brighter than one they had previously seen at the same location. High rates can reflect fatigue, poor attention, or advanced true field loss

A test with poor reliability cannot be reliably interpreted. The doctor will repeat it, and recent changes on an unreliable test should not be acted on.

3. Numerical Plot

The raw data: a grid of numbers showing the dimmest light the patient saw at each location, in decibels (dB). Higher numbers are better. Most clinical interpretation is done off the next two plots, not directly from these raw numbers.

4. Gray Scale (Middle Left)

A visual representation. Each test point is shaded from white (full sensitivity) to black (no light seen). At a glance you can see the shape of any vision loss - central, peripheral, an arcuate curve, a vertical step, etc.

A normal field looks mostly white with a slight darkening at the very edge. A glaucomatous field often shows arcuate (bow-shaped) darkening above or below the horizontal meridian.

5. Total Deviation and Pattern Deviation Plots

The two most clinically important plots:

Total Deviation

Compares each point in your field to age-matched normal values. Points worse than expected are flagged.

Pattern Deviation

Removes the effect of any generalized depression of sensitivity (from cataract, mild media opacity, or just lower overall lighting in the test) and isolates localized defects.

If a patient has an early cataract, their total deviation might look diffusely darker, while their pattern deviation may reveal a specific localized glaucomatous defect underneath. In advanced or very diffuse loss, pattern deviation can become less helpful.

Each plot has both a numerical version (showing the deviation at each point in dB) and a probability symbol version (using shaded squares to indicate whether each point is below the 5%, 2%, 1%, or 0.5% probability threshold for normal).

6. Global Indices (Bottom Right)

The headline numbers:

• Mean deviation (MD) - the average sensitivity across the field, compared to age-matched normal. Negative values mean below normal. MD around 0 dB is normal. MD around -5 dB is mild loss; -10 dB is moderate; -20 dB is severe.
• Pattern standard deviation (PSD) - the roughness of the field. A field that is uniformly depressed (like cataract) has a low PSD; a field with focal loss against a normal background (like early glaucoma) has a high PSD.
• Visual field index (VFI) - a percentage (0-100%). 100% is a perfect field; lower numbers indicate worse function. VFI is heavily weighted toward the central field, especially the central 10°, so a field with preserved central vision but substantial peripheral loss can still have a deceptively high VFI.
• Glaucoma hemifield test (GHT) - flags asymmetry between upper and lower halves of the field, which is a pattern characteristic of glaucoma. Common results include "within normal limits," "borderline," "outside normal limits," and generalized sensitivity warnings.

What Different Patterns Suggest

Glaucoma Patterns

• Arcuate scotoma - a curved area of loss starting near the blind spot and bowing toward the nasal field
• Nasal step - a step-like loss along the horizontal meridian on the nasal side
• Paracentral defect - a small island of loss within the central 10°
• Hemifield-predominant loss - late glaucoma can involve most of the upper or lower field
• The defect typically respects the horizontal midline (above or below) and is more pronounced superior than inferior in many cases

Neurological Patterns

• Bitemporal hemianopia - both eyes lose the temporal half; respects the vertical midline. Suggests chiasmal compression or other chiasm-level disease.
• Homonymous hemianopia - both eyes lose the same side; respects the vertical midline. Suggests an optic tract or post-chiasmal lesion.
• Quadrantanopia - loss of one quadrant; classically temporal lobe lesions involving Meyer's loop cause a contralateral superior quadrantanopia, while parietal lobe lesions cause a contralateral inferior quadrantanopia

These patterns are best interpreted with both eyes' fields side by side.

Retinal Patterns

• Central scotoma - a dense area of loss in the center, typical of macular disease
• Ring scotoma - a circular band of loss, classical for retinitis pigmentosa
• Sector defect - a wedge of loss matching a vascular territory in branch retinal artery occlusion

Functional Patterns

• Tunnel vision that does not expand with greater test distance on confrontation or tangent-screen testing - suggests functional (non-organic) vision loss

Spotting Progression

A single field is a snapshot. The doctor cares more about the trend over multiple visits. Most modern perimeters provide:

• Guided Progression Analysis (GPA) - automatically compares each new test to the patient's baseline and flags points of statistically significant change
• VFI trend graph - a line plot of VFI over time; the slope indicates rate of progression
• Series of fields side by side - comparing recent tests to baseline visually

Reliability is critical here too. A "decline" on an unreliable test should not be treated as real until it is reproduced.

Practical Tips for the Test

A more reliable test gives a better report:

• Be well-rested; visual fields are tiring tests, particularly the longer SITA-Standard strategy
• Bring your glasses or current prescription so the technician can set the correct trial lens
• Keep your eyes fixed on the central target - looking around is the biggest source of fixation losses
• Press the button only when you actually see a light, not when you think you should - false positives invalidate the test more than missed responses
• Ask the technician for a break if you are getting tired; some tests can be paused
• Tell the technician about your prior tests - if you have done dozens, you are probably an expert

When the Field Does Not Match the Optic Nerve

A common scenario: the visual field looks worse than the doctor's view of the optic nerve, or vice versa. Possible reasons:

• Test variability - fields from a single visit are noisy
• Early disease - the structure-function relationship is imperfect in early glaucoma; nerve fiber loss may precede field loss, or the nerve may look normal in the presence of neural loss
• Cataract or media opacity - depresses field but does not affect the nerve
• Functional vision loss - psychogenic loss does not match the optic nerve
• Different disease - atypical patterns prompt a search for non-glaucomatous causes (compressive lesion, demyelinating disease)

Frequently Asked Questions

Why is my mean deviation negative?

Negative MD means below normal. The number is the difference, in decibels, between your average field sensitivity and the average for someone your age with healthy eyes. A small negative value (e.g., -1 dB) is essentially normal; -5 dB suggests mild loss; -20 dB is severe.

My VFI dropped from 92% to 88%. Is that bad?

Maybe. A 4-point drop on a single test could be real progression or could be test variability. The doctor will look at the trend over multiple tests, the corresponding OCT findings, and your other clinical features. A few-point drop on one test does not by itself trigger a treatment change.

Why does my doctor want me to repeat the field?

Visual fields are noisy. A single test is rarely sufficient evidence to act on a change. The standard practice is to repeat any new field defect within a few months and confirm it is reproducible before changing treatment. Multiple confirmed fields showing the same defect or worsening trend is the standard for treatment decisions.

What if my reliability indices are bad?

The test is essentially uninterpretable, and the doctor will set it aside. Patients improve at field testing with practice - the third or fourth test is usually significantly more reliable than the first. Some patients with significant cognitive impairment cannot do reliable field testing at all and require alternative assessments.

What is the difference between SITA-Standard and SITA-Faster?

SITA-Faster is a newer, shorter strategy that gives results in roughly half the time of SITA-Standard. Studies have shown comparable accuracy for most clinical purposes. The trade-off is that switching strategies between visits can introduce a small artifact, so doctors usually pick a strategy and stay with it.

Can a normal field rule out glaucoma?

A normal field cannot fully rule out early glaucoma - structural damage on OCT can precede field loss by years. The doctor uses both structure (nerve appearance and OCT) and function (visual field) together. A normal field is reassuring, but it does not by itself define the diagnosis or stage.

Related Reading

• Visual Field Test - how the test is performed
• Just Diagnosed with Glaucoma
• How to Read Your OCT Report

References