Visual field evaluation

1. Visual field evaluation ESCRS Dr Fiona Rowe University of Liverpool

2. 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.

3. Visual pathway and topography • Retina • Optic disc • Optic nerve • Optic chiasm • Optic tract • Lateral geniculate body • Optic radiations • Visual cortex

4. Retina • Papillomacular bundle – fovea • Nasal retina • Superior retina • Inferior retina • Temporal retina • Central fibres develop first

5. Representation of retinal nerve fibres Optic disc

6. Fibres become myelinated Representation of retinal nerve fibres Optic nerve

7. 13mm wide Surrounded by pituitary gland, third ventricle, thalamus, cavernous sinus Crossing of nasal retinal fibres Superior (above), inferior (below), macular (central) Optic chiasm

8. 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)

9. 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 Lateral Geniculate Body

10. 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 Optic radiations

11. Termination of visual nerve fibres – synapse Occipital lobe – calcarine fissure Fovea; tip of occipital pole (posterior) Temporal crescent; most anterior Superior (above), inferior (below) Visual Cortex

12. Humphrey Analysis • Threshold or suprathreshold analysis • Off-centred equal spacing of central stimuli • Disease specific peripheral presentations

13. Octopus Analysis • Physiology related test pattern • Higher density of stimuli in central field • Follow nerve fibre bundle layer patterns

14. 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

15. 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

16. Polar analysis • Topographic map correlating areas of the visual field (A) with areas of the optic disc (B).

17. 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

18. ≈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

19. 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

20. 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

21. 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

22. 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

23. Aids to interpretation Knowledge of visual pathway and: Related visual field defects Related signs Related symptoms

24. Retina and optic disc Reduced visual acuity Afferent pupillary defect Reduced colour vision Reduced contrast sensitivity Perceptual problems

25. Optic nerve Reduced visual acuity Afferent pupillary defect Reduced colour vision Reduced contrast sensitivity

26. Optic chiasm Postfixational blindness Hemifield slide See saw nystagmus Bowtie atrophy

27. Optic tract Afferent pupillary defect Optic atrophy; asymmetrical

28. 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

29. Visual cortex 90% without other neurological signs Reading difficulties Cortical blindness Riddoch phenomenon Anton’s syndrome

30. 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

31. 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

32. 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

33. Choice of Perimeter

34. 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

35. Over to you!