How automated perimetry measures visual function and helps ophthalmologists monitor glaucoma over time.

Senior patient with one eye covered looking into the bowl of an automated perimeter during a glaucoma visual field test while a technician monitors the test
During automated perimetry, one eye is tested at a time while the patient watches a central target and presses a button when a light is seen.

Glaucoma can damage the optic nerve gradually, sometimes before any change in vision becomes noticeable. A visual field test is one of the main tools ophthalmologists use to detect changes in visual function and monitor established glaucoma.

The resulting printout may contain dark regions, numbers, and probability maps that seem difficult to interpret. Each provides a different piece of information, and none should be considered in isolation.[1, 2]

What Is a Glaucoma Visual Field Test?

The visual field includes everything visible while the eyes remain focused straight ahead, including areas above, below, and to either side of the fixation point.

Glaucoma may reduce sensitivity in particular regions of the visual field, even when the familiar eye-chart measurement of central visual acuity remains good.

The most widely used examination is standard automated perimetry, often performed with a Humphrey Field Analyzer. One eye is tested at a time while the other is covered.

During the test, small points of light appear at different positions inside a bowl-shaped instrument. Each response helps estimate the dimmest light that can be detected in a particular location.

Because the goal is to measure sensitivity rather than performance, not every light is meant to be visible. The examination is painless and requires continued attention to a central fixation target.[2]

What Do Dark Areas on a Visual Field Test Mean?

A common part of the printout is a grayscale map. In general, darker areas indicate regions of lower measured light sensitivity.

A small natural blind spot is also present in a typical visual field because of the position where the optic nerve leaves the eye.

Glaucoma may produce characteristic patterns, however, a dark region does not automatically represent permanent glaucoma damage.

Cataracts, drooping eyelids, incorrect trial lenses, dry eye, fatigue, and inconsistent fixation may also affect the grayscale appearance. Ophthalmologists review additional maps and the overall examination before drawing conclusions.[1, 2]

The grayscale image is also not a literal simulation of a person's day-to-day vision. The visual system can compensate for missing information, and the printed map does not directly reproduce that experience.

How Reliable Is a Single Visual Field Test?

Automated perimetry depends partly on concentration, positioning, and responses during the examination.

Common sources of variation include fatigue, dry eye, distraction, blinking, and the learning effect associated with unfamiliar testing.

The report therefore contains reliability indicators, including fixation losses, false-positive responses, and false-negative responses.

These measures require interpretation in context; for example, false-negative responses may be more common in advanced glaucoma, even without poor cooperation.

An unexpectedly worse result may lead to repeat testing, particularly when the change is inconsistent with optic nerve examination or optical coherence tomography (OCT).

One abnormal or worse visual field does not, by itself, establish glaucoma progression.[1, 2]

What Is the Difference Between a 24-2 and a 10-2 Test?

The 24-2 visual field evaluates a relatively broad area around central fixation and is commonly used in glaucoma diagnosis and monitoring.

The 10-2 visual field concentrates more closely on the central 10 degrees and uses more densely spaced test locations there. It can help characterize defects that are near the center of vision and may not be fully captured by a traditional 24-2 examination.

Research has demonstrated that some central defects found with 10-2 testing may be missed by 24-2 testing.

The selection of a testing strategy therefore depends on the optic nerve, OCT findings, prior field patterns, and clinical concerns.[1, 4, 5]

How Is Glaucoma Progression Determined?

A central purpose of regular visual field testing is to identify reproducible change over time rather than reacting to an isolated darker area.

Ophthalmologists compare serial examinations for newly appearing defects, enlargement or deepening of existing defects, and statistically meaningful trends in summary measurements.

Evaluation also considers intraocular pressure, OCT measurements of retinal nerve fiber and ganglion cell structures, and the appearance of the optic nerve.

OCT assesses structure, while visual field testing assesses function.

Changes in these measurements do not always appear at the same time, making the combination particularly useful.[1]

What Helps Produce a Useful Visual Field Test?

The quality of the examination can improve when patients understand the testing process.

The technician typically assists with positioning, provides the appropriate optical correction when needed, and explains the fixation target and response button.

Normal blinking, appropriate pauses for discomfort or fatigue, and maintaining focus on the central target can help limit avoidable artifacts.

The test is designed to identify the threshold of detection; missing some very dim lights is expected.

Key Takeaway

A glaucoma visual field report is more than its grayscale picture.

The distribution of sensitivity loss, reliability indicators, summary indices, and changes across repeated examinations all help ophthalmologists interpret optic nerve function.

Visual fields are most informative when assessed alongside OCT, intraocular pressure, and examination findings.

Inland Glaucoma Center uses visual field testing and optic nerve imaging as part of comprehensive glaucoma evaluation and monitoring. Request an appointment or call 909-315-6891.

Medical information notice: This article is intended for general educational purposes only. It is not individualized medical advice, a diagnosis, or a treatment recommendation. Interpretation of clinical testing requires consideration of the complete eye examination and medical history.

Works Cited

  1. Gedde SJ, Bowden EC, Challa P, et al. “Primary Open-Angle Glaucoma Preferred Practice Pattern®.” Ophthalmology. Published online February 9, 2026. https://doi.org/10.1016/j.ophtha.2025.12.029
  2. Ramulu P, et al. “Standard Automated Perimetry.” EyeWiki, American Academy of Ophthalmology. https://eyewiki.aao.org/Standard_Automated_Perimetry
  3. “Humphrey Visual Field.” StatPearls. NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK585112/
  4. De Moraes CG, Hood DC, Thenappan A, et al. “24-2 Visual Fields Miss Central Defects Shown on 10-2 Tests in Glaucoma Suspects, Ocular Hypertensives, and Early Glaucoma.” Ophthalmology. 2017;124(10):1449–1456. https://doi.org/10.1016/j.ophtha.2017.04.021
  5. Susanna FN, Melchior B, Paula JS, et al. “Variability and Power to Detect Progression of Different Visual Field Patterns.” Ophthalmology Glaucoma. 2021;4(6):617–623. https://doi.org/10.1016/j.ogla.2021.04.004