Visual field evaluation

ESCRS

Dr Fiona RoweUniversity 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

• Retina• Optic disc• Optic nerve• Optic chiasm• Optic tract• Lateral geniculate body• Optic radiations• Visual cortex

Retina

• 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

• 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• Values• Comparison• Probabilities• Defect (Bebie) curve• Diffuse defect• Global indices• Cluster Graph• Polar Graph

• Global Trend

• Cluster Trend • PolarTrend

• 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

• Correlation between structural changes (imaging of retinal nerve fibre layer) and functional changes (visual field result)

• 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 W-W 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:– Cataract– Increased variability of threshold– Tiring and difficult test – reliability issues– Long test duration– Considerable learning curve

Factors influencing visual fields; Artefacts

• 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

• Reduced visual acuity• Afferent pupillary defect• Reduced colour vision• Reduced contrast sensitivity• Perceptual problems

Optic nerve

• Reduced visual acuity• Afferent pupillary defect• Reduced colour vision• Reduced contrast sensitivity

Optic chiasm

• 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 comparisonSurface 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 comparisonSurface 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 PerimeterGoldmann Octopus Humphrey

ManualKineticPeripheralBlind spotPoor VA / fixationAdvanced defectsDriving

Manual AutomatedKineticStaticPeripheralCentralSensitive to early lossRepeatability Blind spotPoor VA / fixationAdvanced defectsDriving

AutomatedStaticCentralSensitive to early lossRepeatability Driving

Common choices• First visit

– Screen 24-2 SITA fast, G TOP– Screen: glaucoma 24-2SITA standard,

G dynamic– Pathology 24-2 SITA standard,

G dynamic• Follow-up 24-2/30-2 standard,

G dynamic• Constricted field 10-2, LV• Hydroxychlorequine Macula, M dynamic• Peripheral pathology 60-4, Kinetic• DVLA 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

rowef@liv.ac.uk