3.4 Visual field screening (confrontation, Amsler)

Screening the Visual Field

The visual field is everything a fixating eye can see, both central and peripheral. Screening tests let a COT detect gross field loss quickly at the chair, flagging patients who need formal automated perimetry (such as a Humphrey visual field). The two staple bedside tools are confrontation visual fields and the Amsler grid.

Confrontation Visual Fields

Confrontation testing compares the patient's peripheral field to your own (assumed normal). It is quick, needs no equipment, and screens for large defects such as hemianopias and quadrantanopias.

Technique

1. Sit about 1 meter (arm's length) directly facing the patient at eye level.
2. Test one eye at a time: the patient occludes one eye, and you close your opposite eye so your fields match theirs.
3. Ask the patient to fixate on your open eye or your nose and not to look toward the target.
4. Present fingers (or a small target) in the mid-periphery of each of the four quadrants: superior-temporal, superior-nasal, inferior-temporal, and inferior-nasal, midway between you and the patient.
5. Ask the patient to count fingers or report when they see them move, and compare their response to your own field.

You can also present targets simultaneously in both hemifields to detect extinction/neglect, in which the patient sees each side alone but ignores one side when both are shown (a parietal-lobe sign). Document each quadrant as full or defective.

Interpreting patterns

The location of loss helps localize the lesion along the visual pathway:

Confrontation is a screen, not a substitute for formal perimetry: it catches only fairly large or dense defects and can miss early glaucomatous or subtle loss.

The Amsler Grid

The Amsler grid tests the central 10 degrees of the visual field, the macula-dominated area responsible for detailed central vision. It is the key screen for macular disease, especially age-related macular degeneration (AMD).

How to administer

1. The grid is a square of horizontal and vertical lines with a central dot.
2. Hold it at the patient's normal reading distance (about 14 in / 30 cm) with reading correction on.
3. Test one eye at a time, with the patient fixating the central dot.
4. Ask a set of questions: Can you see the center dot? Are all four corners and edges visible? Are any lines wavy, bent, blurred, or missing? Are any areas dark or empty?

What abnormal findings mean

• Metamorphopsia, in which straight lines appear wavy or distorted, is a hallmark of macular fluid or edema, classically wet (neovascular) AMD. New or worsening metamorphopsia is an urgent finding.
• A scotoma, a blurred, dark, or missing area, indicates focal macular or optic-nerve loss.

Patients at risk are often given a grid for home monitoring, testing one eye at a time daily and reporting any new distortion immediately, because early wet AMD responds better to prompt anti-VEGF treatment. Record which eye showed which finding, ideally with a sketch.

When to Refer to Formal Perimetry

Screening findings guide the next step. Refer for formal automated perimetry (standard automated perimetry / Humphrey) when:

• Confrontation shows a defect or a suspicious hemianopic pattern.
• The patient has or is suspected of having glaucoma; subtle nasal steps and arcuate defects need threshold perimetry, not confrontation.
• Neurologic symptoms suggest a chiasmal or retrochiasmal lesion.
• Baseline documentation and progression monitoring are needed for a known field-affecting disease.

Screening versus formal perimetry

• Confrontation and Amsler: fast, qualitative, chairside; catch gross or central defects; good for triage and home monitoring.
• Automated perimetry: quantitative, reproducible, maps the field point by point; needed for diagnosis and for following glaucoma or neuro-ophthalmic disease.

Always document the method, the eye tested, correction worn, and reliability (patient cooperation), so results can be compared at future visits.

Additional Bedside Techniques

Two quick add-ons strengthen field screening. The physiologic blind spot corresponds to the optic disc, which has no photoreceptors; an enlarged blind spot can point to disc swelling. The red-cap desaturation test compares how vivid a red target looks to each eye: in optic neuritis and other optic-nerve disease the red appears washed-out or dimmer on the affected side, a sensitive early sign that pairs well with the swinging-flashlight test.

Ensuring a reliable screen

• Confirm the patient keeps steady central fixation and does not glance at the target.
• Use a consistent target size and plain background.
• Retest any suspicious quadrant before recording a defect.
• Note patient cooperation and reliability, since fatigue and inattention can mimic real field loss.

Kinetic versus static perimetry

Formal perimetry comes in two forms. Kinetic perimetry (Goldmann) moves a target from non-seeing toward seeing areas to map isopters and is useful for large neurologic defects. Static (standard automated) perimetry presents stationary lights of varying brightness at fixed points and is the standard for glaucoma. Confrontation and Amsler screening decide who needs these more detailed tests.