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Clinical electrophysiology:

Clinical electrophysiology:. Plugging into the visual system. Marlee M. Spafford, OD, MSc, PhD, FAAO. COPE Personal Disclosure. For this lecture, I have: developed the course material independently developed the course material without commercial interests

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Clinical electrophysiology:

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  1. Clinical electrophysiology: Plugging into the visual system Marlee M. Spafford, OD, MSc, PhD, FAAO

  2. COPE Personal Disclosure For this lecture, I have: • developed the course material independently • developed the course material without commercial interests • no personal conflicts of interest • no financial relationship with a commercial interest

  3. Basic Electrodiagnostic Equipment • Specialized computer hardware & software • >$100,000 Cn Pattern stimulator Ganzfeld (flash stimuli) http://www.diagnosysllc.com/home/

  4. Visual Electrodiagnostic Tests • Electroretinogram (ERG) • Electro-oculogram (EOG) • Visually Evoked Potential (VEP)

  5. Electroretinogram (ERG) • Reflects global changes in retinal electrical potential in response to flash or pattern stimuli http://webvision.med.utah.edu/ClinicalERG.html

  6. Electro-oculogram (EOG) • Records the ocular standing electrical potential • Dark-adapted with light-adapted • Reflects gross outer retina/RPE function + - http://webvision.med.utah.edu/ClinicalERG.html http://brainconnection.positscience.com/med/medart/l/eye-xsection-side.gif

  7. Visually Evoked Potential (VEP) • Assess macular-cortical pathway’s gross integrity Record http://www.metrovision.fr http://www.aph.org/cvi/brain.html

  8. Patient #1: 6-yr-old male • VEP referral (family OD): • Reduced VA, not corrected by spectacles: meridional amblyopia? • OD: -1.00/-3.00 x 170 6/12 • OS: -2.00/-3.50 x 180 6/15 • Interview: • Ocular Hx: • 1st Rx@ 4 yrs • Nyctalopia: “always trips in the dark” • Health Hx: • Unremarkable • Birth Hx: • Polydactyl (surgery @ 1 yr) • Negative family hx of eye disease • 1 step-brother (“normal” vision) • No parental consanguinity http://www.medes-salud.com.ar/causas.htm

  9. Nyctalopia • Causes: • Retinitis pigmentosa (RP) • Choroideremia • Congenital stationary night blindness (CSNB) • Pan-retinal laser surgery • Vitamin A deficiency • Non-retinal • Night myopia • Optical defects (e.g., cataract) • Problem Specific Testing: • DFE • Visual fields • Automated > 30o; Goldmann • ERG (full field ERG) • Colour Vision • adults; B-Y & R-G defects

  10. DFE http://www.scielo.br.proxy.lib.uwaterloo.ca/scielo.php?script=sci_arttext&pid=S0004-27492009000500019&lng=en&nrm=iso&tlng=en

  11. Bardet-Biedl Syndrome Cardinal Features (4 of 6) • Retinal dystrophy (RP) • Polydactyly • Obesity • Cognitive impairment • Hypogonadism • Nephropathy • AR inheritance • 1/179 carry gene • Progressive vision loss • Nyctalopia • Constricted Fields • Acuity loss • Optometrist duties: • Low vision care • Referral for genetic work-up • Referral to nephrologist

  12. Retinal-based Function Tests • ERG • Full-field ERG: fERG (typical referral) • Pattern ERG: pERG • Multi-focal ERG: mfERG • EOG

  13. Full-field ERGs • Assess the gross integrity of the outer 2/3rds of the neural retina • Good test for: • widespread retinal diseases • vision loss that changes with lighting conditions fERG http://webvision.med.utah.edu/ClinicalERG.html

  14. fERGs • Standardized fERG protocol exists: • ISCEV standard: 2008 (International Society for Clinical Electrophysiology of Vision) • Dark adapt (>20 min): scotopic ERGs (rod-isolated & rod-cone mixed) • Light adapt (>3 min): photopic ERGs (cone-isolated) http://webvision.med.utah.edu/ClinicalERG.html

  15. Measuring fERGs • a-wave: Amplitude & implicit time • b-wave: Amplitude & implicit time http://webvision.med.utah.edu/ClinicalERG.html

  16. fERG Components • a-wave:Photoreceptors • b-wave:Müllers & On-Bipolars • Oscillatory potentials (OPs):Amacrines http://webvision.med.utah.edu/ClinicalERG.html

  17. ISCEV Recording Electrodes • Gold Standard • Contact lens electrode (e.g., Burian-Allen Speculum Contact Lens Electrode) • Bipolar electrode design • CL: active • Speculum: reference http://fn.bmjjournals.com/content/82/3/F233.abstract

  18. ISCEV Recording Electrodes • Other ISCEV Electrodes • DTL Fiber • Gold foil • HK loop http://www.nature.com/eye/journal/v21/n6/fig_tab/6702309f2.html http://www.diagnosysllc.com/products/product5.php

  19. DTL Fiber Electrode Insertion

  20. Ganzfeld View

  21. Chin Rest Prep

  22. ERG Recording

  23. ERG Recording

  24. Simulated fERG Normative Database(Amplitude [µV]: 20-39 yrs) S P Supernormal = > 100th percentile WNL = ≥ 5th percentile Diminished = < 5th percentile

  25. Diagnostic Uses of fERG • Inherited retinal disorders • RPE photoreceptor disease, photoreceptor disease, chorioretinal dystrophies, vitreoretinal dystrophies • Retinal ischemic disease • diabetic retinopathy, central retinal vein occlusion, carotid artery stenosis, sickle cell retinopathy • Pre-surgical evaluation • obstructed retina due to cataract, hemorrhage or penetrating injury • Retinal toxicity • hydroxychloroquine • Unexplained vision loss

  26. fERG: RPE-Photoreceptor Disease rod maximal flicker cone http://webvision.med.utah.edu/ClinicalERG.html

  27. fERG: Photoreceptor Disease rod maximal flicker cone http://webvision.med.utah.edu/ClinicalERG.html

  28. fERG: Photoreceptor Disease rod maximal flicker cone http://webvision.med.utah.edu/ClinicalERG.html

  29. pERG(seldom done) • Reflects central retinal response (incl. ganglion cell) • Macular disease • Toxic/nutritional disease • Unexplained central vision loss • 2012 ISCEV standard http://www.diagnosysllc.com/home/ http://www.iscev.org/standards/perg.html

  30. mfERG • 2011 ISCEV standard • Topographical measure of outer 2/3rds of retina • ~60-100 small retinal areas • Local ERGs are mathematical extractions of the signal • Dilated pupils; fiber electrode www.Cephalon.dk http://webvision.med.utah.edu/ClinicalERG.html

  31. Diagnostic Uses of mfERG • Macular disease • e.g., Stargardt Disease, ARMD • Unexplained central vision loss

  32. mfERG ARMD mfERG Normal mfERG

  33. Electro-oculogram (EOG) • Seldom done • 2010 ISCEV standard • Reflects global outer retina/RPE function • Clinical diagnostic use: • Bestvitelliform macular dystrophy (rare, AD inheritance) EOG http://img.medscape.com/pi/emed/ckb/ophthalmology/1189694-1227128-71.jpg

  34. EOG • Eyes have a ‘standing potential’ • Cornea positive; RPE negative • Derived from RPE; changes with retinal illumination • Potential decreases in dark; increases in light • Test involves: • Making lateral saccades through a dark & light phases + - http://www.iscev.org/standards/pdfs/eog-standard-2006.pdf http://brainconnection.positscience.com/med/medart/l/eye-xsection-side.gif

  35. EOG Arden Ratio • Light peak (LP)/dark trough (DT) • >2.0: normal • 1.5 to 2.0: borderline • <1.5: abnormal http://www.iscev.org/standards/pdfs/eog-standard-2006.pdf

  36. Patient #2: 9-yr-old male • VEP referral (family OD): • Fine, mostly pendular, horizontal nystagmus, photodysphoria & reduced VA: albinism? • OD: +3.00/-1.00 x 150 6/24 • OS: +2.50/-0.50 x 020 6/21 • Interview: • Ocular Hx: • Congenital nystagmus • Health Hx: • Unremarkable • Negative family hx of eye disease/low vision • No parental consanguinity http://www.kilgorevision.com/stories.htm

  37. Ocular Albinism (OA) Main Features • Sl. lighter hair & skin complexion (not necessary) • Nystagmus(most horizontal & pendular) • Iris tranillumination • Macular hypoplasia • Fundushypopigmentation • Visual pathway decussation abnormality • X-linked recessive (GPR143 mutation at Xp22.3-22.2) • Evidence of carrier status • iris illumination • ‘mud-spattered’ fundus • hypopigmented skin macules • Optometrist duties: • Strabismus Dx/Mx • Low vision care • Referral for genetic work-up

  38. Albinism: Problem Specific Testing • Ocular Motility • Iris tranillumination • DFE • VEP • OCT (nystagmus preclude?) http://journals1.scholarsportal.info/tmp/1186526813808035824.pdf

  39. Visually Evoked Potential (VEP) • Assess macular-cortical pathway’s gross integrity Record http://www.metrovision.fr NOTE: VEP = VER = VECP (latter 2: older terms) http://www.aph.org/cvi/brain.html

  40. Visually Evoked Potentials (VEPs) • Types of clinical-based VEPs • Pattern: pVEP • 2009 ISCEV standard • Full-field: fVEP • 2009 ISCEV standard • One example of research-based VEPs • Sweep: sVEP • No ISCEV standard yet

  41. VEP Stimuli pVEP fVEP NOTE: pVEPscan be reversing checkerboards or gratings http://www.metrovision.fr http://webvision.med.utah.edu/ClinicalERG.html

  42. ISCEV Recording Electrodes • Scalp silver-silver chloride or gold disc surface electrodes • ISCEV standard: • 1 active (3 better) plus 1 reference electrode www.lkc.com

  43. VEP Electrode Placement • International 10-20 system for electrode placement ISCEV Ref ISCEV Active z http://www.brainmaster.com

  44. VEP Electrode Placement • Multi-channel placement • Pre-chiasmal: Better • Post-chiasmal: Required OZ http://www.opt.indiana.edu http://www.brainmaster.com

  45. Measuring pVEPs P100: • Cortical response (Amplitude in μv) to checkerboard reversal (IT: Implicit time ~100ms) Transient VEP (<4Hz) Amp IT http://www.iscev.org/standards/pdfs/vep-standard-2004.pdf

  46. Simulated pVEP Normative Database(Implicit Time [ms]: 20-39 yrs) WNL = ≤ 5th percentile Delayed = > 5th percentile

  47. Measuring fVEPs P2: • Cortical response to 1 Hz flash stimulus (amplitude in μv; IT: Implicit time ~100ms) • fVEP useful when pVEP fails Amp IT http://www.iscev.org/standards/pdfs/vep-standard-2004.pdf

  48. Diagnostic Uses of pVEP • Optic nerve disease • Optic neuritis (recovery more than dx); compressive optic neuropathy; Leber’s hereditary optic neuropathy (LHON) • Post-chiasmal disease (with multiple-channels) • Demylinating disease; ocular albinism • Amblyopia • Psychogenic vision loss • Unexplained vision loss

  49. Optic Neuritis http://opt.pacificu.edu/test/index.html

  50. Visual Pathway Asymmetry Albinism ~55% decussate ~80% decussate ++ ++ ++ + ++ +++ http://www.nature.com/eye/journal/v21/n10/images/6702839f3.jpg

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