Visual field evaluation

Report
Visual field evaluation
ESCRS
Dr Fiona Rowe
University of Liverpool
Goals
• Visual pathway anatomy
• Methods of perimetry use for Humphrey visual field
analyser, Goldmann perimeter, Octopus 900 perimeter
• Visual field printout options
• Interpretation of results using statistical packages
provided by the perimeter systems
• Discussion of the ocular symptoms and signs associated
with lesions along the various parts of the visual pathway
• Possible localisation of lesion according to type of visual
field defect plotted
• Artefacts of visual field defects and their avoidance.
Visual pathway and topography
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Retina
Optic disc
Optic nerve
Optic chiasm
Optic tract
Lateral geniculate body
Optic radiations
Visual cortex
Retina
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Papillomacular bundle – fovea
Nasal retina
Superior retina
Inferior retina
Temporal retina
• Central fibres develop first
Optic disc
• Representation of
retinal nerve fibres
Optic nerve
• Fibres become
myelinated
• Representation of
retinal nerve fibres
Optic chiasm
• 13mm wide
• Surrounded by
pituitary gland, third
ventricle, thalamus,
cavernous sinus
• Crossing of nasal
retinal fibres
• Superior (above),
inferior (below),
macular (central)
Optic tract
• Sweep laterally from chiasm around hypothalamus and
ventral portion of midbrain
• Regroup of fibres – inexact pairing
• Ipsilateral temporal and contralateral nasal retinal fibres
• Superior (superomedially), inferior (inferolaterally)
Lateral Geniculate Body
• Diencephalon, midbrain
• First synapse of retinal nerve
fibres
• Rotate through 90 degrees
• Superior (medial), inferior
(lateral)
• 6 layers
• Macular fibres in all 6 layers
• Ipsilateral temporal fibres; 2,
3, 5
• Contralateral nasal fibres; 1,
4, 6
Optic radiations
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90 degree realignment of nerve
fibres
Superior (above),
inferior
(below)
3 groups
– Upper and central pass
directly to visual cortex via
posterior temporal and
parietal lobes
– Lower loops anteriorly and
laterally around inferior horn
of lateral ventricle (Meyer’s
loop) via temporal lobe to
visual cortex
Visual Cortex
• Termination of visual
nerve fibres – synapse
• Occipital lobe – calcarine
fissure
• Fovea; tip of occipital
pole (posterior)
• Temporal crescent; most
anterior
• Superior (above), inferior
(below)
Humphrey Analysis
• Threshold or suprathreshold analysis
– Off-centred equal spacing of central stimuli
– Disease specific peripheral presentations
Octopus Analysis
• Physiology related test pattern
– Higher density of stimuli in central field
– Follow nerve fibre bundle layer patterns
Analysis
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Values
Comparison
Probabilities
Defect (Bebie) curve
Diffuse defect
Global indices
Cluster Graph
Polar Graph
• Global Trend
• Cluster Trend
• PolarTrend
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Absolute thresholds
Scales and defect depth
Percentile of normality
Ranking of defect values
Deviation from 50th %
Mean sensitivity and defect
Analysis of regional deviations from normal
All local defects mapped to a
representation of the optic disc for
structure/function comparison
• Change rate, fluctuation and significance
calculation
• Regional change rate and significance
calculation
• Pointwise linear regression analysis
mapped to the optic disc
Structure versus Function
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Correlation between structural changes (imaging of retinal
nerve fibre layer) and functional changes (visual field result)
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Structural changes at the optic nerve head and/or retinal nerve
fibre layer tend to precede visual field changes early in the
disease
Polar analysis
• Topographic map correlating areas of the visual field (A) with
areas of the optic disc (B).
Function specific perimetry
• Standard achromatic perimetry (white on white)
detectable only when a substantial number of ganglion
cells lost (≈ 30%)
• Functional evaluation of retinal ganglion cells for early
detection of glaucoma
• Temporally modulated stimuli are more sensitive than WW perimetry
• Functional tests isolate subpopulations of retinal
ganglion cells which lose function earlier than other
ganglion cell types
• ≈80% parvocellular ganglion cells
– Sensitive to colour and contrast
– High pass resolution perimetry
• ≈ 15% magnocellular ganglion cells
– Sensitive to temporally
modulated stimuli
– Critical fusion frequency
– Frequency doubling technology
• ≈ 5% koniocellular ganglion cells
– Sensitive to blue-yellow
components
– B-Y perimetry
Function specific perimetry
• HRP: High-pass resolution
perimetry
• Ring shaped targets of 14
different sizes used to determine
resolution of central 30 degrees
of visual field
Function specific perimetry
• CFF: Critical fusion frequency
perimetry
• Measurement of flickering stimulus at
different locations ranging from slow to fast
(0-50Hz) speed until the stimulus appears to
be a continuous light rather than flickering
• Not sensitive to lens changes, e.g. cataract
• FDT: Frequency doubling technology
• Detects the sensitivity for discriminating the
frequency doubling stimulus
• Stimulus is a large 10 x 10 square of black
and white bars, flickering at 25 Hz
Function specific perimetry
• SWAP: Short-wavelength automated perimetry
• Isolates blue sensitivity (S cones) from green (M) and red (L) cones by
suppressing the relative sensitivity of M and L cones with a bright yellow
background and using a blue stimulus
• S- cones become more sensitive
• Practical restrictions:
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Cataract
Increased variability of threshold
Tiring and difficult test – reliability issues
Long test duration
Considerable learning curve
Factors influencing visual fields;
Artefacts
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Anatomical features of the face
Ptosis
Miotic pupil
Uncorrected refractive error
Refractive corrections
Cataract
Attention of the patient
Technique of the examiner
Aids to interpretation
Knowledge of visual pathway and:
• Related visual field defects
• Related signs
• Related symptoms
Retina and optic disc
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Reduced visual acuity
Afferent pupillary defect
Reduced colour vision
Reduced contrast sensitivity
Perceptual problems
Optic nerve
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Reduced visual acuity
Afferent pupillary defect
Reduced colour vision
Reduced contrast sensitivity
Optic chiasm
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Postfixational blindness
Hemifield slide
See saw nystagmus
Bowtie atrophy
Optic tract
• Afferent pupillary defect
• Optic atrophy; asymmetrical
Optic radiations
• Temporal lobe lesion
– central achromatopsia, agnosia, alexia,
hallucinations, seizures, Bell’s reflex
– normal depth and motion
• Parietal lobe lesion
– reduced stereopsis, spatial localisation and
motion, agnosia, reduced OKN, poor fixation,
left/right confusion, Bell’s reflex, hemiparesis
– normal colour and form, discrimination and
recognition of faces
Visual cortex
• 90% without other neurological signs
• Reading difficulties
• Cortical blindness
– Riddoch phenomenon
– Anton’s syndrome
Differential diagnosis
• Horizontal meridian respected in retinal and
optic nerve head lesions
• Vertical meridian respected in chiasmal and
post chiasmal lesions
• Bilateral defects in post chiasmal lesions
• Deterioration of vision, RAPD, fundus
abnormalities seen in pre chiasm lesions
• Case history
Perimeter comparison
Surface luminance (apostilb:asb)
Stimulus luminance
•Luminance adjusted by combination of neutral-density filters
•Graded in decibels (dB). Each dB equivalent to 0.1 log unit
•10dB equals 1 log unit or 10-fold change in intensity
Stimulus luminance
•Goldmann and Octopus perimeters generate a maximum stimulus luminance
(0 dB) of 1,000 asb
•Humphrey perimeter uses a 10,000-asb bulb (0 dB)
•Range of stimulus intensity greater for Humphrey
Perimeter comparison
Surface background luminance
•Goldmann and Humphrey instruments use 31.5 asb, while past Octopus models use 4 asb
•Octopus 900 use 31.4 asb
Stimulus duration
•100ms for Octopus
•200ms for Humphrey
Programme strategies
•Humphrey perimetry: SITA analysis and threshold standard or fast bracketing strategies
•Octopus perimetry: Peritrend analysis and threshold dynamic or TOP strategies
Choice of Perimeter
Goldmann
Octopus
Humphrey
Manual
Kinetic
Peripheral
Blind spot
Poor VA / fixation
Advanced defects
Driving
Manual
Automated
Kinetic
Static
Peripheral
Central
Sensitive to early loss
Repeatability
Blind spot
Poor VA / fixation
Advanced defects
Driving
Automated
Static
Central
Sensitive to early loss
Repeatability
Driving
Common choices
• First visit
– Screen
– Screen: glaucoma
– Pathology
• Follow-up
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Constricted field
Hydroxychlorequine
Peripheral pathology
DVLA
24-2 SITA fast, G TOP
24-2SITA standard,
G dynamic
24-2 SITA standard,
G dynamic
24-2/30-2 standard,
G dynamic
10-2, LV
Macula, M dynamic
60-4, Kinetic
Estermann
Over to you!
Summary
• Visual pathway anatomy
• Visual field results for kinetic and static
perimetry
• Artefacts of visual fields
• Aids to interpretation and localisation of
lesion
[email protected]

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