Visual Fields II

Key step before starting a visual field test

• Explain the test clearly to the patient

• How is it going to work?

• What they need to do?

• Why you are doing the test?

What are the room lighting requirement for visual field testing?

• Room lighting needs to be dimmed

• consider dark adaptation

Refractive correction during visual field testing

• Contact lens wearers can wear lenses while performing test

• otherwise full aperture lenses can be used for other ametropes → full to prevent artefact scotoma

• ensure lens close enough to eye (prevent artefact scotoma)

How is trial lens power determined?

• Patients Rx can be entered

• field analyser will calculate a trial lens

how can we ensure patient comfort during visual field testing?

• ensure machine at correct height for px

• px shouldn’t be hunched over

• test takes a while so ensure px comfortable → increases reliability as if not comfortable may loose focus

What is the Purpose of gaze monitoring?

• Ensures the patient maintains fixation throughout the test

Why is encouragement important during testing?

• test will take a number of mins

• usually more if there is a defect

What does WANDER stand for ?

• W – What was used

• A – Accuracy

• N – Normal or not

• D – Defect + (what type)

• E – Evaluate

• R – Review/Repeat

W in WANDER example

• What test and parameters were used

• Name of test, what target used , stimulus , background illumination, which eye tested

• patient demographics (age, pupil size , refractive correction

pupil size, date + time of test)

A in WANDER

• Accuracy and reliability of the test

> Need to consider:

• Fixation losses

• False positives

• False negatives

Fixation losses definition

• used to check if eye looking at target

• flagged at 20%

• 30% considered more accurate cut-off

• monitor yourself + make a decision

What does gaze tracking measure?

• eye movements using purkinje images

• upward detection = eye movements

• downward deflection = loss of signal → blinking etc

• relies on subjective assessment of whether you think fixation was good enough

What are False positives?

• “trigger happy” patient

• px respond when NO stimulus presented

• high false positives → happy clicker, randomly press button in hopes of passing test

• poor understanding of test → instruct them properly

• should be <20%

What are False negatives?

• failure to respond to supra threshold target

• associated with fatigue or inattention

• should be <20%

• may be better to repeat on another day if not improved with repeat

N in WANDER

• is field Normal or not

look at:

• threshold values

• Greyscale plot

• Total deviation

• Pattern deviation

• Glaucomal hemifield Analysis

Global indices

• mean deviation (MD)

• Pattern Standard deviation

What do Threshold values show?

• exact threshold value for every point tested

• higher numbers = higher sensitivity, px can detect very dim lights

• low numbers → lights need to be very bright for patient to see them = poor sensitivity

• triangle indicates position of blind spot

• look for clusters of points with reduced sensitivity

What is the Purpose of the greyscale plot?

• Visual representation of raw threshold values, where darker spots indicate poor sensitivity → problem areas

• doesn’t consider age of px , or change in threshold with retinal eccentricity

• main purpose to demonstrate problem areas to your patient → why you referred them

What is the Total deviation plot ?

• compared with age-matched normal value → difference shown on plot

• positive numbers → px performed above average

• negative values → worse than average

• p- value shows statistical significance of any abnormal value → also takes into account retinal eccentricity

What is the purpose of Pattern deviation?

• takes all values from total deviation plot , orders them numerically + selects the 7th highest value

• value subtracted from each of numbers on total deviation plot

• reduces effects of diffuse loss → sensitivity depressed due to cataract or refractive blur

• → defects which show up on this plot more suggestive of pathological change in visual pathway

Mean deviation (MD)

• mean difference in decibels between expected hill of vision (normal) and patients hill of vision

• monitor overall change in patients visual field

What is Pattern standard deviation (PSD)?

• amount by which shape of hill of vision differs from expected

• low value → little difference

• High value → irregular shape

What is the Purpose of the Glaucoma Hemifield Test (GHT)

• Detect glaucomatous field loss

• compares symmetry of superior field against inferior field in 5 predetermined zones

• (glaucoma tends to produce arcuate defects that respond to horizontal midline)

• values from PD plot in each zone scored + compared in the 2 hem fields

Possible GHT outcomes

• Within normal limits

• borderline

• outside normal limits

• general reduction in sensitivity

• abnormally high sensitivity

GHT outside normal limits definition

• At least one zone pair differs at <1% of normal subjects

GHT borderline definition

At least one zone differs between 1–3% of normal subjects.

D in WANDER

Describe the defect

• Altitudinal

• Arcuate

• Constriction

• Nasal step

• Heminopia

• Quadrantanopia

• Scotoma → central , paracentral Caecocentral

What is an Altitudinal defect?

> involves both quadrants of either the superior or inferior field

What is an Arcuate defect?

• follows pattern of retinal nerve fibres (in an arc, radiating from disc)

• Typical in glaucoma → obeys horizontal midline

What is a Constriction defect?

• Shrinking of entire visual field (in towards the centre)

e.g Retinitis pigmentosa

What is Nasal step?

• characteristic of early glaucoma → obeys horizontal midline

• affecting nasal retina

What is a Hemianopia ?

• Affects one half of Visual Field → 2 quadrants

• respects vertical midline

• Highly congrues

affects back of head → stroke, tumour

• e.g pituitary tumour

What is Quadrantanopia ?

• affects one quadrant of Visual field

• if temporal →tumour, aneurysm, stroke

What is a Scotoma ?

• localised defect

• may be absolute (no vision at all) or relative (reduced visual function)

• 3 types:

• Central , paracentral and Caecocentral

What other terminology can be used to describe defects?

• Homonymous → same side of space

• Heteronymous → affects opposite sides of space

• Unilateral → one eye

• Bilateral → both eyes

• Congruity → level of similarity between 2 eyes

E in WANDER

• Evaluate what disease is suggested

• progression

R in WANDER

Review or repeat to confirm findings

• new defect is NOT a defect until repeated

• need to consider effects of learning + fatigue