Part 5 | How to Read an HVF 24-2 Visual Field: A Practical Guide for Glaucoma Testing

A Humphrey Visual Field, often called an HVF, is one of the most important tests used to evaluate and monitor glaucoma. While OCT scans help doctors evaluate the structure of the optic nerve, the HVF helps evaluate function — meaning how well a patient is actually seeing across different areas of their visual field.

One of the most commonly used visual field tests in eye care is the 24-2 visual field. This test checks points across the central 24 degrees of vision and helps detect patterns of vision loss that may occur with glaucoma, optic nerve disease, retinal disease, or neurologic conditions.

For many patients, the printout can look confusing. There are numbers, shaded maps, dots, symbols, and reliability scores. But eye doctors read the HVF in a systematic way.

Infographic for OPT-ISM Eye Care Blog on reading a 24-2 visual field, with doctor, patient, eye charts, and glaucoma tips.

What Is an HVF 24-2?

An HVF 24-2 is an automated visual field test that measures a patient’s sensitivity to light in different areas of their vision.

During the test, the patient looks straight ahead and presses a button whenever they see a small light appear. Some lights are bright and easy to see. Others are dimmer and more difficult to detect. The machine uses the patient’s responses to create a map of the visual field.

The “24-2” refers to the area and spacing of the test points. It evaluates the central 24 degrees of vision, with test points spaced 6 degrees apart.

This test is commonly used in glaucoma because many glaucoma defects occur in predictable patterns within this tested area.

Eye-care blog poster reading Start With Reliability, with doctor and patient reviewing charts beside a monitor.

Step 1: Check Reliability First

Before interpreting any visual field, the first question is:

Can we trust this test?

Visual field testing depends heavily on patient attention, understanding, and consistency. A patient may perform poorly if they are tired, anxious, distracted, uncomfortable, or new to the test.

Important reliability indicators include:

Fixation Losses

Fixation losses suggest the patient may not have kept their eye looking straight ahead during the test. If the patient looked around, the map may not accurately represent their true visual field.

False Positives

False positives occur when the patient presses the button even though no light was shown. This can happen when someone is overly eager or trying too hard to respond quickly.

High false positives can make the visual field look better than it really is.

False Negatives

False negatives occur when the patient misses a light that should have been visible based on earlier responses.

High false negatives may suggest fatigue, inattention, advanced disease, or inconsistent test performance.

Test Duration

A long test time may indicate the patient was struggling or becoming fatigued. Fatigue can create artificial depression on the visual field.

If the test is unreliable, it may need to be repeated before making clinical decisions.

Infographic from OPT-ISM Eye Care Blog showing a doctor and patient reviewing visual field maps, with tips on reading 24-2 printouts.

Step 2: Look at the Grayscale — But Do Not Stop There

The grayscale map is often the easiest part of the visual field printout to understand because it looks like a shaded picture of the patient’s field.

Darker areas suggest reduced sensitivity.

However, the grayscale can be misleading. It can exaggerate defects and may be affected by cataracts, dry eye, small pupils, poor focus, poor test performance, or media opacity.

The grayscale is useful for a quick impression, but it should never be the only part of the test used for interpretation.

Step 3: Compare Total Deviation and Pattern Deviation

The total deviation map compares the patient’s visual sensitivity to an age-matched normal population.

It shows areas where the patient performed worse than expected for their age.

Total deviation can show both diffuse and localized depression. Diffuse depression may occur from cataracts, poor testing, small pupils, uncorrected prescription, corneal issues, or retinal disease.

The pattern deviation map adjusts for generalized depression and helps highlight localized defects.

This is especially important in glaucoma because glaucoma often causes localized nerve fiber layer defects rather than uniform dimming of the entire visual field.

Pattern deviation is often more helpful for identifying early glaucomatous defects.

Step 4: Review the Probability Plots

Probability plots use symbols to show how likely it is that a specific test point is outside normal limits.

Common probability levels include:

• Less than 5%

• Less than 2%

• Less than 1%

• Less than 0.5%

The lower the percentage, the less likely that point is normal.

A single abnormal point may not mean much, but a cluster of abnormal points in a glaucoma-like pattern is more concerning.

Eye care blog infographic titled MD, PSD, and VFI Explained, showing doctor and patient with visual field test numbers and charts.

Step 5: Understand MD, PSD, and VFI

HVF reports include summary numbers that help describe the field.

Mean Deviation, or MD

Mean deviation gives an overall measurement of how depressed the visual field is compared to normal.

A more negative MD generally means more field loss.

For example, a mildly abnormal field may have a small negative MD, while more advanced damage may have a significantly more negative MD.

Pattern Standard Deviation, or PSD

Pattern standard deviation measures irregularity in the field.

A high PSD may suggest localized loss, which is common in glaucoma.

PSD can be especially helpful in early to moderate glaucoma but may become less useful in very advanced disease.

Visual Field Index, or VFI

VFI is a percentage estimate of remaining visual field function.

A VFI close to 100% suggests near-normal function. A lower VFI suggests more functional loss.

VFI is often useful for monitoring progression over time.

Infographic from OPT-ISM Eye Care Blog on common 24-2 glaucoma patterns, showing five visual field defects and a doctor-patient exam.

Step 6: Look for Common Glaucoma Patterns

Glaucoma often follows the anatomy of the retinal nerve fiber layer. Because of this, visual field defects often appear in recognizable patterns.

Common glaucoma patterns on HVF 24-2 include:

Nasal Step

A nasal step is a defect along the nasal side of the visual field that respects the horizontal midline.

This is a classic glaucoma finding.

Arcuate Defect

An arcuate defect curves from the blind spot toward the nasal visual field.

This pattern follows the arc-like course of the retinal nerve fibers.

Paracentral Defect

A paracentral defect occurs near central fixation.

These defects are important because they may affect reading or daily visual function earlier than peripheral defects.

Superior or Inferior Field Loss

Glaucoma often affects one half of the field more than the other.

Damage to the inferior optic nerve or inferior RNFL often causes superior visual field loss. Damage to the superior optic nerve or superior RNFL often causes inferior visual field loss.

Step 7: Compare With Prior Visual Fields

One visual field is only a snapshot.

The most meaningful information often comes from comparing multiple fields over time.

Your eye doctor looks for:

• Repeatable defects

• Worsening MD

• Worsening VFI

• Expanding scotomas

• New localized defects

• Defects that match the optic nerve or OCT

A suspicious visual field should usually be repeated to confirm that the defect is real.

Why an Abnormal HVF Does Not Always Mean Glaucoma

Visual field defects can occur for many reasons besides glaucoma.

Possible causes include:

• Cataracts

• Dry eye

• Poor test reliability

• Uncorrected prescription

• Retinal disease

• Optic nerve disease

• Neurologic disease

• Eyelid obstruction

• Small pupils

• Patient fatigue

That is why the HVF must be interpreted with the full eye exam, OCT, optic nerve appearance, eye pressure, corneal thickness, and medical history.

HVF 24-2 and Glaucoma Monitoring

For glaucoma patients and glaucoma suspects, the HVF 24-2 helps answer an important question:

Is the disease affecting vision, and is it getting worse?

The test helps monitor functional vision loss over time.

When paired with OCT imaging, optic nerve examination, and eye pressure measurements, the HVF becomes a powerful tool for detecting and managing glaucoma.

Key Takeaways

The HVF 24-2 measures visual function.

A good interpretation starts with reliability.

The grayscale gives a quick impression, but the total deviation, pattern deviation, probability plots, MD, PSD, and VFI provide deeper information.

Glaucoma defects often follow recognizable patterns such as nasal steps, arcuate defects, paracentral defects, and superior or inferior field loss.

The most meaningful visual field defects are repeatable and match the optic nerve or OCT findings.

Schedule a Glaucoma Evaluation in Tampa

At OPTISM, we use visual field testing to help evaluate glaucoma, optic nerve disease, and unexplained vision changes.

If you have elevated eye pressure, a family history of glaucoma, suspicious optic nerves, or prior abnormal testing, a comprehensive eye exam can help determine whether further monitoring or treatment is needed.

Early detection matters because glaucoma often has no symptoms in the beginning.