2. Non-Automated Visual Field Techniques

non-automated instruments

  • Non-automated screening methods for visual field defects form part of routine eye examinations.

  • Screening protocols reduce testing time substantially, typically to a few minutes, making visual field testing a viable option for screening for disease.

  • Common non-automated screening visual field techniques include:

    • Confrontation

    • Amsler Grid

    • Bjerrum/Tangent Screen.

Confrontation

  • Sensitive only to gross, dense visual field losses

    • provides a preliminary indication of visual field loss.

  • Confrontation should be performed monocularly on all patients.

  • Spectacle correction: test is usually uncorrected so central and peripheral testing occur together; if the patient has high refractive error, correct for central testing and remove correction for peripheral testing.

Procedures

  • Record visual fields as seen from the patient’s perspective, not how it appears to you.

  • Label the eye tested (RE or LE) and clearly mark nasal and temporal directions to ensure the record is unambiguous.

  • Targets should be presented against an appropriate background so that they are readily detectable by normal observers.

  • Ideally, the examiner should have their back against an evenly illuminated wall free from distracting objects or potential glare sources (lamps, windows).

Communication and patient interaction

  • Clearly explain procedures to patients.

  • Typical wording cues: the examiner will describe peripheral vision tests in simple terms and ask for a specific response.

    • “I’m just going to examine your peripheral / side vision with a couple of simple tests”

  • Example approach: tell the patient you will examine the peripheral/side vision with simple tests, then give direct prompts to elicit the desired responses (eg, look at the examiner's nose and watch for finger movements).

  • Avoid vague questions; use precise prompts to elicit the expected answers.

Facial Amsler (Confrontation sub-method)

  • Facial Amsler uses facial features as landmarks to determine central versus quadrant defects.

Facial Amsler: Procedures

  • One eye occluded; patient fixates on the examiner's nose.

  • Ask the patient whether the examiner's other facial features appear distorted or missing (eg, eyes, ears, mouth).

  • Interpretation:

    • Nose distortion = central scotoma.

    • Distortion of other facial features indicates absolute or relative scotoma.

  • Record the field from the patient’s perspective:

    • RE Facial Amsler: NAD

    • RE Facial Amsler: Central distortion.

Confrontation - Finger Counting Fields (FCF)

  • Occlude one eye; patient fixes on the open eye.

  • Hold up 1 or 2 fingers in the top two quadrants, straddling the vertical and horizontal midlines.

    • Ask for the total number of fingers seen; repeat for the bottom two quadrants.

  • Number of questions: four (two per eye, top and bottom quadrants) to screen both eyes (Anderson et al 2009).

  • Rationale: testing each quadrant individually can miss extinction, a phenomenon where a target is not seen in the affected hemisphere when two targets are presented simultaneously.

  • Extinction is a form of hemi-spatial neglect that often arises after stroke or brain injury.

Quick reference: sufficient responses

  • A rapid finger-counting confrontation screening uses four responses from the patient; examples include combinations in which the correct responses are two, three or four, and never one.

Confrontation: Colour Comparison

  • Red desaturation can be an early indicator of neurological visual field defects.

  • Procedure: place two red targets in two quadrants that straddle the vertical and horizontal midlines; ask if there are any noticeable colour differences in redness.

  • Subtle colour defects involving perception may be revealed by changes in saturation and hue.

Static and Kinetic Finger Movement (Confrontation procedures)

  • Static Finger Movement: examiner uses finger movement in each quadrant; patient indicates which side movement occurs (one side or both).

  • Kinetic Finger Movement: examiner uses finger movement or a large Traquair target to assess peripheral extent of the field along eight cardinal directions

    • patient reports when the finger/target is detected

    • an isopter is created for a single target.

Kinetic Finger Movement: Procedure details

  • Setup: examiner and patient sit facing each other at the same eye level, about 1 m apart; both cover one opposing eye with their palm.

  • Movement: wiggle fingers from the periphery in a plane equidistant between the two faces; move the target at a constant rate.

  • The patient indicates when the target is first seen; the location is compared to the examiner’s visual field.

  • Things to remember:

    • The temporal field is often greater than 90 degrees, so it may not be possible to reach the far limit of the patient’s field.

    • Facial contours (prominence of the nose, recession of the eyes, brow prominence) may affect the visual field.

    • Consider whether the visual field loss is anatomical or pathological.

Confrontation - Recording and documentation

  • Always record what you do and the results:

    • Facial Amsler: Normal

    • Finger Count: 4 quadrants normal

    • Colour Comparison: Colour loss noticed in RE right upper field

    • Peripheral Fingers: RE and LE normal in 8 directions

Amsler Chart

  • A qualitative test of the central visual field (~10°).

  • Detecting central and paracentral scotomas, as well as areas of distorted vision

  • Assessment of patients with ocular diseases where scotomas or distortion exist close to fixation, eg. macular degeneration

  • Advantages: rapid, easy, portable; suitable for home visits and self-monitoring.

Amsler Chart: Procedures

  • Standard chart: grid of white lines on a black background; held at a working distance of 30 cm from the patient; at this distance the chart extends to about 10° from fixation.

    • Each 5 mm square subtends a visual angle of 1° at 30 cm.

  • Correction: an appropriate lens is required for the working distance, particularly for presbyopes

    • patient’s own reading spectacles may be suitable only if single-vision

    • if px wears multifocals or bifocals use a trial frame.

  • Procedure: view the chart with one eye while fixating the central spot

    • indicate any areas where lines are missing or distorted (metamorphopsia).

  • Recording: defects should be recorded on the chart

    • it is often useful for patients to note deficits themselves.

Patient instructions

  • "We are now testing the central vision of your right eye. Look at the centre dot, but be aware of the background at all times.“

    • “Can you see the central dot?”

    • “Can you see all 4 corners of the card? How about all 4 sides?”

    • “Are all the lines straight and even?”

    • “Are any of the squares missing?”

    • “Are any of the lines wavy or distorted?"

Amsler variations

  • Red printed charts have been proposed to aid detection of toxic retinal conditions.

  • Some charts include diagonal lines through the center to assist fixation for patients with central scotomas.

Amsler recent research interest

  • There is increased clinical and research interest in central field assessment for detecting ocular disease.

  • Screening for wet AMD prior to anti-VEGF treatment: systematic review (mostly case control studies)

    • Values from 12 studies: sensitivity and specificity of 78% and 97%

    • Highlighted the importance of correct instruction and monitoring

  • In glaucoma, a study of 106 eyes (53 patients) showed that Amsler grid detected moderate to severe central glaucomatous loss

    • Compared Amsler results with 10-2 VF (HFA)

    • Sensitivity and specificity of 68% and 92%

    • Useful where more sophisticated VF tests are unavailable

Bjerrum/Tangent Screen

  • The Bjerrum screen (also known as the Tangent Screen) measures the central 30deg at 1 metre.

  • Uses Kinetic strategy

  • Technique requires skilled and experienced examiners.

Bjerrum/Tangent Screen: Procedures

  • Screen is a black felt surface with eccentricities, meridians, and blind spots stitched onto it

  • screen illuminance of 10 lux

  • Targets consist of painted discs or beads moved at 5 deg/s (usually from non-seeing to seeing)

Plotting and recording

  • Plot blind spots first using a 5/1000W target in the eight cardinal directions.

  • Plot isopters using a 2/1000W moving target from the periphery inward until seen; continue inward to fixation.

  • If the target disappears, this indicates a scotoma.

  • Smaller or coloured targets may be used to plot additional scotomas.

  • Black map pins are used to record the visual field on the screen and then transposed to printed charts.

  • For reduced distraction, the examiner should wear a black sleeve or dark clothing.

Isopter notation

  • Isopters are described as A/BC, for example 1/2000W.

  • A = target size (mm); B = test distance (mm); C = colour of the target.

Non-Automated Visual Field Techniques: General Considerations

  • These qualitative non-automated tests are influenced by the following factors:

    • Type, size, colour, and brightness of the target used.

    • Distance at which the test is carried out.

    • Speed of target movement.

    • Background against which the test is performed.

  • These tests are crude screening tools; if there is any indication of an abnormal field, an automated field test should be performed for more objective assessment.