Visual field testing — the formal mapping of what each eye can see across its full range — is one of the most useful diagnostic tools in ophthalmology, and especially in low vision evaluation. For patients with macular degeneration, glaucoma, stroke, or other conditions affecting parts of the visual field, perimetry quantifies what’s gone, what remains, and how to make the most of remaining vision.
What a visual field test actually measures
The eye has a wide field of view — roughly 160-180 degrees horizontally and 120 degrees vertically when looking straight ahead. Within that range, sensitivity to light is not uniform. The fovea (very center) is the most sensitive; sensitivity declines moving outward. Disease processes affect specific zones in characteristic patterns.
Visual field testing presents standardized stimuli of varying brightness across the field while the patient maintains fixation on a central target. The test maps where stimuli are seen and not seen, producing a quantitative description of the patient’s functional visual field.
What perimetry can detect
- Central scotomas — blind spots in central vision, characteristic of macular degeneration and macular conditions
- Arcuate defects — characteristic glaucoma patterns affecting nasal field
- Hemianopia — loss of half the visual field, typically from stroke or brain tumors
- Constriction — overall narrowing, characteristic of advanced glaucoma or retinitis pigmentosa
- Quadrantanopia — loss of one quarter of the visual field, often from cortical strokes
- Central island — preserved central vision with widespread peripheral loss, found in advanced glaucoma
Why it matters for low vision
Patients with low vision often live with a complex pattern of preserved and lost areas across their visual field. A formal map of that pattern is essential for:
- Driving evaluations — most states require specific visual field criteria for licensure. Perimetry quantifies the field for medical determination.
- Reading and daily task adaptations — knowing where the preserved islands of vision are allows targeted training to use eccentric viewing positions effectively.
- Mobility training — orientation and mobility specialists use perimetry results to teach safe travel strategies.
- Magnification device prescription — the right type and power of low-vision aid depends on the size and location of the patient’s preserved vision.
- Disease monitoring — comparing serial perimetry over time detects progression earlier than relying on patient symptoms alone.
Types of visual field testing
Standard automated perimetry (SAP)
Most common type. The Humphrey Visual Field Analyzer is the workhorse — patient sits in front of a bowl-shaped device, maintains central fixation, and presses a button when small flashing lights appear in peripheral vision. Standard 24-2 or 30-2 protocols cover the central 24-30 degrees of the visual field, which captures most clinically relevant pathology.
Frequency-doubling technology (FDT) perimetry
Faster, less fatiguing. Useful for screening or for patients who tire easily.
Goldmann (manual) perimetry
Older technique still used for specific situations — large field testing, follow-up of patients with very advanced visual field loss, or specific neurological cases. The examiner moves test stimuli manually.
Microperimetry
For low vision patients, microperimetry uses a video monitor to test sensitivity at specific retinal locations while tracking the patient’s actual fixation. Useful for evaluating macular degeneration and identifying preferred retinal loci for eccentric viewing.
What patients can expect during the test
You’ll sit in front of the perimeter device with one eye covered. You’ll be asked to keep looking at a central target throughout the test (this is hard — the natural urge is to look toward where you see the flash). When you see a peripheral flash of light, you press the button.
The test takes 4-8 minutes per eye depending on protocol. Some flashes will be very faint and might be missed; others will be obvious. Both are part of the test design. Most patients describe the test as tedious rather than difficult.
Interpreting the results
Visual field results are presented as grayscale and numerical maps. Darker areas represent reduced sensitivity. Two key indices summarize the test: Mean Deviation (overall visual field loss compared to age-matched normal) and Pattern Standard Deviation (how irregular the field is, sensitive to localized defects). Reliability indices (false positives, false negatives, fixation losses) indicate whether the patient performed the test consistently.
How often to repeat
For glaucoma patients, visual field testing is typically performed every 6-12 months depending on stage and stability. For low vision patients, repeat testing depends on the underlying condition’s expected stability. Sudden visual field changes warrant prompt repeat testing and evaluation.
The role in comprehensive low vision care
Visual field testing is one element of a broader low vision evaluation that may also include best-corrected acuity, contrast sensitivity, color vision, and functional assessment of reading and daily tasks. Together these give a comprehensive picture of what someone can see — and inform what aids and adaptations will help most.
For more on neuro-ophthalmologic evaluation including visual field interpretation, see the Neuro-Ophthalmology page.
