9.12  Automated Visual Fields

Humphrey Monocular Visual Fields

Humphrey Visual Fields (HVFs) are often presented at data stations. Visual fields that are commonly tested include glaucomatous (usually respecting the horizontal meridian) and neuro-ophthalmic (usually respecting the vertical meridian) pathology. Candidates should pay special attention to reliability, artefacts and describing visual fields in general terms. Ideally, all HVFs should be correlated with clinical examination.

1. Describe the Type of Field

  • Name
  • Age of patient
    • Age determines the likelihood of particular diseases. Results are compared against age-matched normal values
  • Right eye or left eye
  • Date of exam
Test Pattern

30-2

Tests central 30° of fixation. This may be preferable for monitoring disease progression

24-2

24-2 Tests central 24° superior, inferior and temporal; 30° nasal

10-2

Tests central 10° of fixation. Better for conditions with a small central scotoma such as can occur in optic neuritis and drug-induced optic neuropathies

NB: -2 strategy involves grid test points 6 apart offset from vertical and horizontal meridian

Reliability

i. Fixation monitor

  • “Gaze/blindspot” means that both the gaze tracker and the blindspot have been used to detect fixation losses

ii. Fixation target

  • “Central” = foveal

iii. Fixation losses

  • The blindspot is mapped first. If the patient responds when this area of visual field is re-tested, it means that the patient has moved their eye. Fixation losses exceeding 20% may indicate a compromised test

iv. False Positive Errors

  • Number of times the patient responds when no stimulus is present. False positive rates exceeding 15% may indicate a compromised test

v. False Negative Errors

  • Number of times a patient fails to respond to a stimulus brighter than previously determined threshold value at that location. A high false negative rate may indicate fatigue, inattention or malingering

vi. Test Duration

  • A lengthy test may suggest poor reliability

vii. Gaze Tracker

  • Timeline of fixation behaviour. Upward deflection represents eye movements, downward deflection indicates gaze cannot be detected (e.g. blinks). Excessive periods of poor fixation may be associated with reduced reliability
Stimulus Size
  • Usually Goldmann size III, but may be increased in advanced glaucoma
Stimulus Colour
  1. White stimulus (standard white-on-white)
  2. Red stimulus. There is some evidence that this may be preferable for drug induced maculopathies.
  3. Short-wavelength automated perimetry (SWAP) uses a blue stimulus on yellow background. Blue-on-yellow perimetry deficits are an early indicator of glaucomatous damage and may also be useful in detecting neuro-ophthalmologic deficits more readily than standard white-on-white
Background
  • Usually 31.5 apostilbs
Strategy
  1. SITA Standard™ (Swedish Interactive Threshold Algorithm). This is a mathematical model that produces a personalized test, allowing for faster testing with minimal compromise in accuracy compared with full threshold testing
  2. SITA Fast™. This may be preferred if reliability is compromised by a long test in a slow patient
  3. Full threshold
Pupil Size
  • Miotics may reduce sensitivity of tests
Visual Acuity
Rx
  • Spectacle prescription used in the test

2. Describe the Field Defect

Raw Test Results
  • Numeric sensitivity (dB) and gray scale graphical representation of visual field sensitivity with darker areas depicting lower sensitivity. The gray scale is often the least useful plot
Total Deviation Probability Plot
  • Indicative of a patient’s sensitivity compared to normal age-corrected sensitivities at each location. The numerical scale expresses this in decibels (lower than expected sensitivities are given negative values). The probability plot has progressive stippling representing whether the sensitivity at a particular location is worse than the lowest 0.5%, 1%, 2% and 5% of an age-matched normal population
Pattern Deviation Probability Plot
  • This is the most useful of all the plots, except in advanced visual field loss when even the best points are severely depressed. It indicates localized visual field loss by correcting for any generalized depression. A uniformly depressed total deviation and normal pattern deviation may indicate cataract; a normal total deviation and abnormal pattern deviation may indicate a “trigger-happy” patient

3. Glaucoma Hemifield Test (GHT)

Glaucomatous visual field changes usually respect the horizontal midline. The Glaucoma Hemifield Test assesses the probability of glaucoma by comparing the superior and inferior visual fields. It should never be used alone to diagnose glaucoma. The result may be:

  1. Outside Normal Limits
    1. If the sensitivity in at least 1 of 5 zones in the superior visual field are significantly different (p < 0.01) to those in the mirror-image inferior visual field
  2. Borderline
  3. General Depression of Sensitivity or Abnormally High Sensitivity
  4. Within Normal Limits

4. Global Indices

These provide comparisons with age-matched normative values.

Mean Deviation (MD)

A weighted average of the total deviation is compared with the normal population. Negative values indicate overall sensitivity is lower than normal

Pattern Standard Deviation (PSD)

General indicator of the degree of localized visual field loss. A high PSD is indicative of irregularities in field

Pathological Visual Fields

Analyse both the left and right visual fields and describe the defects. Look for patterns of loss:

A. Glaucomatous Patterns

  1. Paracentral scotomas
  2. Arcuate scotomas
  3. Nasal steps

B. Neurological Patterns

Optic Nerve (Unilateral)

Enlarged blind spot (disc swelling)
Altitudinal hemianopia e.g. non-arteritic anterior ischaemic optic neuropathy

Optic Chiasm

Bitemporal hemianopia

Optic Tract

Homonymous (matching defects)
Become more congruous towards the occipital lobe

Artefacts

Inexperienced Patient

Many patients will demonstrate an improvement in visual fields after one or two attempts. Always be cautious in over-interpretation of the first visual field

Ptosis

Reduced sensitivity in the superior portion of the central field (gray scale)

Lens Artefact

A high plus lens will contract the visual field. This may manifest as a marked, sudden reduction in peripheral sensitivity

Cloverleaf

Sensitivity is better in the central points of each quadrant but poor elsewhere.

This characteristic pattern is indicative of patients who fail to respond after the early testing period.

“Trigger Happy” Patient

This is evident by high false positives, a “white” greyscale, normal total deviation but abnormal pattern deviation and an “Abnormally High Sensitivity”

Figure 9.12.1 Normal HVF (Left)

Figure 9.12.1
Normal HVF (Left)

Contents

Figure 9.12.2
Bitemporal Hemianopia (Bilateral)
Bitemporal hemianopia secondary to a pituitary macroadenoma.

Figure 9.12.2
Bitemporal Hemianopia (Bilateral)

Bitemporal hemianopia secondary to a pituitary macroadenoma.

Figure 9.12.2
Bitemporal Hemianopia (Bilateral)
Bitemporal hemianopia secondary to a pituitary macroadenoma.

Figure 9.12.3
Clover-Leaf Artefact (Left)

Clover-Leaf artefacts represent good concentration during the initial stages of the test (when the central points of each quadrant are tested), followed by fatigue and loss of concentration during testing of the surrounding points.

Figure 9.12.4 End-Stage Glaucoma (Right)

Figure 9.12.4
End-Stage Glaucoma (Right)

Both the 24-2 and 10-2 demonstrate involvement of fixation

Figure 9.12.4 End-Stage Glaucoma (Right)

Figure 9.12.5
Enlarged Blind Spot (Right)

Enlarged right blindspot secondary to optic disc swelling

Figure 9.12.6
Inferior Altitudinal Hemifield Defect (Left)

Inferior altitudinal hemifield defect secondary to Non-Arteritic Anterior Ischaemic Optic Neuropathy with superior optic disc swelling.

Figure 9.12.7
Right Inferior Arcuate Scotoma

Figure 9.12.8
Inferior Scotoma Secondary to Advanced Glaucoma (Left)

Figure 9.12.9 Superior Quadrantinopia (Left-Bilateral)

Figure 9.12.9
Superior Quadrantinopia (Left-Bilateral)

Figure 9.12.9 Superior Quadrantinopia (Left-Bilateral)

Figure 9.12.10 Homonymous Hemianopia (Right – Bilateral)

Figure 9.12.10
Homonymous Hemianopia (Right – Bilateral)

Figure 9.12.10 Homonymous Hemianopia (Right – Bilateral)

Esterman Binocular Visual Fields

The Esterman visual field is the most commonly performed suprathreshold test for bilateral visual field loss. Its main utility lies in the assessment of a person’s ability to drive safety. The test is available on the Humphrey Field Analyser and does not require any fixation monitoring, to resemble the real-world driving environment. Points are not evenly spaced, with more points spaced near the horizontal midline. Peripheral field criteria for a driver’s licence varies between different driving authorities, although generally speaking, 110 degrees of horizontal and 20 degrees of vertical field is required.

Figure 9.12.11 Esterman Visual Field (Binocular)

Figure 9.12.11
Esterman Visual Field (Binocular)

This patient would be ineligible to drive.

          

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