reclaim the periphery - new approaches to old issues
TRANSCRIPT
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Reclaim the periphery!New approaches to old issues
Lars Frisn
Institute of Neuroscience andPhysiology/OphthalmologyGteborg University, Sweden
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CAP
Terraincognita
Kinetic
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By definition, contractions proceed centripetally.Periphery test is required for early diagnosis.
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Generally, it seems reasonable toexpect that any progressive
disorder that ends up in a centralfield remnant should involve somecontraction and/or peripheraldepression at an early stage
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Progressive concentric depression & contraction.Periphery test may aid early diagnosis.
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Concentric visual field contractions
- Optic nerve hypoplasia
- Vigabatrin toxicity
- Idiopathic
- Fictitious- Somatoform (functional,
hysterical
)
- Fatigue
- Perioptic neuropathy
- Chronic papilledema
- Glaucoma
- Tapetoretinal degenerations
- Drusen of the nerve head
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- Anterior V1: loss of temporal crescent
Diagnosis requires periphery test
Examples oflocalized contractions
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- lateral geniculate body
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Retinotopy is less clear for the pathways
- good peripheral tests may well be useful
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- optic nerve hypoplasia
Frisn & Holmegaard: Spectrum of optic nerve hypoplasia.
Br J Ophthalmol. 1978; 62:7-15.
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Conditions of recent interest
- epilepsy surgery -> 50 (-100) % VFD
- vigabatrin toxicity -> ~ 50 (-100) % VFD
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Meyers loop
Centennial jubilee coming up!
Adolph Meyer
The connections of the occipital lobes andthe present status of the cerebral visualaffections
Trans Ass Am Physicians 22: 716, 1907
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Williams, Gluhbegovic &Jew: The Human Brain.Harper & Row, 1980
Klingler & Ludwig:Atlas Cerebri Humani.
Karger, 1956
Technique: teasingfreeze-thawed tissue
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Falconer & Wilson 1958 Van Buren & Baldwin 1958
Barton et al. Brain 128: 2123, 2005
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Magnetic resonance tractography
Nilsson, Starck, Ljungberg, Rydenhag & Frisn: Tractographyof the optic radiation after temporal lobe resection (in prep)
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Vigabatrin (Sabril, Sabrilex)
- partial epilepsy- pediatric epilepsyviGABAtrin (gamma-amino-butyric acid)transferase inhibitor
Vigabatrin is toxic to retinal ganglion cellsand/or their axons
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Concentric contraction & peripheral depression- central field remains largely normal
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C-shaped pattern of RNFL atrophyFrisn & Malmgren: Characterization of vigabatrin-associated optic atrophy.
Acta Ophthalmol Scand 81: 466, 2003
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Inclusion of peripheral field data shouldhelp illuminate relationships to opticdisk and nerve fiber layer parameters
~ 1/3 of RNFL axons belong to retinalganglion cells located outside 30
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Periphery is important
What determines the periphery ?
How to access the periphery ?
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For concentric contractions/depressions:focus on the nasal &temporal periphery
Outer limits with and without extra-polarfixation marks and retraction of eyelids:
25%
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Outer limit only is generally inefficient
Aim to assess border zone, i e, slope
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15 LCD screen at 0.25 m distance canaccess 60 - 120 of horizontal eccentricity
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LCD/CRT-based perimeters
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Rarebit micro dot 0.5 x MAR
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HRP, normal eye, right temporal periphery
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Motion perimetry, right nasal periphery(courtesy of Younger & Wall)
Normal
Ocular hypertension
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Rarebit test principles
- use stimuli of minimal subtense(ideally smaller than receptive fields),
- at high & fixed contrast (easy to see)
- check once only for the presence offunction (no thresholding),
- in ever-new, non-overlapping locations;
- calculate Hit Rate =
- exposed briefly (to negate sweep gains),
sum seensum shown
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Normal eyes Subtlecompressionof the chiasm
Rarebit perimetry, right temporal periphery
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3 subjects treated with vigabatrin, ordered bycumulative dose.
Rarebit perimetry, right nasal periphery
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Frisn L: Vigabatrin-associated loss of vision: rarebit perimetry illuminatesdose-damage relationship. Acta Ophthalmol Scand 82: 54, 2004
Rarebit perimetry, ctd
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Blum RG, Gates LK, Jamed BRHow important are peripheral fields?
Arch Ophthalmol 61: 1 8, 1959
- Arc perimeter: 2 mm white target
- 72 (seventy-two!!) examiners
- 3078 eyes
- Tangent screen: 1 mm white target at 1 m
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Reclaim the periphery!
The end
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