Visual Field Testing

Visual Field Testing is 6% of the exam: confrontation screening and automated perimetry, with their technique and artifacts. The assistant runs and records the test; the physician interprets it.

The visual field — everything one eye sees while it holds still on a single point. A normal field reaches roughly 90° or more toward the temple, about 60° toward the nose, 50–60° upward, and about 70° downward. Sensitivity is highest at the center and falls toward the edges, a shape called the hill of vision.

The physiologic blind spot — the optic nerve head has no photoreceptors, so each eye has a blind spot about 15° temporal to fixation. The disc lies nasal to the fovea, so the gap falls in the temporal field: on a printout the right eye's blind spot sits right of center, the left eye's left of center.

Confrontation fields — a rapid screen comparing the patient's field to the examiner's, one eye at a time, four quadrants. It flags gross defects for formal testing.

1. Set up — sit facing the patient about an arm's length away, eyes level. To test the right eye, the patient covers the left eye and looks at your left eye while you close your right eye; the open eyes face each other, so your own field is the comparison.

2. Count fingers in each quadrant — hold your hand midway between you; one, two, or five fingers are the easiest to tell apart. A wiggling finger brought in from outside the field checks its edges. If the patient's eye jumps toward your hand, re-instruct and repeat.

3. Switch eyes and record — each eye separately: full to finger counting, or the quadrant missed.

Its limits — only large, dense defects show; early glaucoma and small scotomas (patches of lost or dimmed vision) pass. The method also assumes the examiner's own field is normal. A normal result does not rule out field loss.

Amsler grid — the central 10° at near, one eye at a time with reading correction: the macular complement to perimetry and the standard home-monitoring tool. The Supplemental Testing guide covers reading it; the Ophthalmic Patient Services and Education guide, home teaching.

Automated static perimetry — stationary stimuli of varying brightness map threshold sensitivity at fixed points: the dimmest light the patient can detect at each point.

Test patterns — 24-2 covers the central ~24° (the glaucoma workhorse); 10-2 packs points into the central 10° for macular disease and advanced glaucoma, and is also used in hydroxychloroquine screening. The pattern comes from the physician's order.

Fast threshold strategies — modern strategies cut test time dramatically compared with older full-threshold (staircase) testing; a shorter test means less fatigue, which itself improves reliability. Follow-up fields normally repeat the earlier pattern and strategy so results can be compared.

On the Humphrey — the Humphrey Field Analyzer, the most widely used automated static perimeter, runs these fast strategies as SITA (Swedish Interactive Thresholding Algorithm) Standard, SITA Fast, and the newest, SITA Faster. Each starts from what is already known about normal and diseased fields to estimate every threshold, reaching accurate values in a fraction of full-threshold time. What changes is how thresholds are found; the stimulus, the test pattern, and testing one eye at a time do not.

Kinetic (Goldmann) perimetry instead moves a target inward until seen, drawing isopters. An operator brings a target of set size and brightness in from the far periphery and marks where the patient first sees it. Joining the marks gives an isopter, the boundary of where that target is visible; a smaller or dimmer target draws a smaller isopter inside it. It is now a special-case tool, for very peripheral disease or patients who cannot manage automated testing.

Frequency doubling technology — FDT offers fast screening for glaucoma with flickering stripes on a compact instrument; abnormal results are confirmed on standard perimetry.

The printout is only as good as the technician's setup.

Timing — perimetry happens before dilation: drops add glare and focusing blur that depress the field. Right eye first by convention, unless the physician directs otherwise.

Patient and position — enter the correct date of birth, because results are compared with normal values for the patient's age. Adjust table and chair so the patient sits upright, chin in the rest and forehead against the bar, both disinfected between patients; a strained patient drifts off center. Keep room lighting dim and consistent.

Occlusion — the fellow eye wears a proper patch: no fingers, no pressure. An eye held shut by effort tires mid-test.

Trial lens — the perimeter bowl, the dome the patient looks into, sits at near range. The patient's own glasses come off (frames and bifocal segments cast shadows), and the holder gets the lens the machine's or clinic's table gives: the distance prescription combined with a near add for the patient's age. Seat it close to the eye and centered.

Artifacts masquerading as disease:

Instruction is half the test — "Keep looking at the center; press when you see a light; many lights are deliberately too dim to see, so missing some is normal; blink normally between lights." Patients told this stay calm; patients not told it hunt for stimuli and fail fixation.

Stay with the patient — watch the patient and the eye monitor, and re-center a drifting head. Fatigue is an artifact: use pauses (hold the response button), encourage, and split long orders across a break.

Reliability indices — fixation losses, false positives, false negatives — record how the test went; watch them during the run, not just after.

False positives deserve the closest watch: they can hide real loss.

The technician recognizes patterns to check plausibility and flag surprises; interpretation is the physician's.

Glaucoma follows the nerve-fiber bundles: arcuate scotomas and nasal steps that respect the HORIZONTAL midline. The bundles arc above and below fixation and never cross the horizontal line, so the loss stops there.

Disease at the chiasm or behind it respects the VERTICAL midline, because from the chiasm back the pathway splits each eye's field down the middle (the General Medical Knowledge guide traces it).

Global indices — Mean Deviation (MD) summarizes overall depression versus age-normal, more negative meaning more loss; Pattern Standard Deviation (PSD) highlights localized loss. Anything that dims the whole field, such as a small pupil or a cataract, also lowers MD.

In glaucoma care the field is read alongside eye pressure (see the Tonometry guide) and OCT nerve fiber scans (see the Ophthalmic Imaging guide).

On the chart — for each eye, right first: the test and pattern, the trial lens, pupil size and any drops, and the reliability indices with a word on cooperation. Add anything that shaped the result (a taped lid, pauses, re-instruction, a restart, a first-ever field), and confirm patient, eye, and date on every printout. The assistant reports findings to the physician and never interprets the field for the patient.

When it cannot wait — most fields are filed for the physician's reading. Some are not: a new dense defect, above all one that respects the vertical midline (bitemporal or homonymous loss), or a field much worse than the last reliable one. Ask when the patient noticed the change, and show these to the physician right away, before the patient leaves. Loss that came on suddenly, or with headache, scalp tenderness, or jaw pain on chewing in an older adult, is an emergency: get the physician immediately (see the General Medical Knowledge guide).

Be ready to locate the blind spot and explain it, run a confrontation field, tell static from kinetic perimetry, match 24-2 and 10-2 to their uses, set up the lens, patch, and lids, explain each reliability index, spot the common artifacts, match the classic defects to their usual source, and sort abnormal fields by urgency.