ELECTRO-DIAGNOSTIC TESTS ( ERG, EOG, VER ) Dr. Ankit M. Punjabi DOMS (final year) Dept. of Ophthalmology, KIMS Hospital Ba...
ERG <ul><li>Electric potential generated by retina in response to stimulation of light.  </li></ul><ul><li>First recorded ...
ERG waves ( a, b, c ) <ul><li>‘ a’  is negative wave. Amplitude is from baseline to trough & implicit time is from onset o...
ERG
ERG <ul><li>‘ a’  origin  photoreceptors </li></ul><ul><li>‘ b’  origin  Muller’s cells + bipolar cells. Mainly from Mul...
Physiologic basis of  ERG <ul><li>a wave  – </li></ul><ul><li>-  Light falling – Hyperpolarisation </li></ul><ul><li>-  Ou...
Physiologic basis of  ERG <ul><li>b wave- </li></ul><ul><li>-  Muller cells – modified astrocytes </li></ul><ul><li>-  No ...
Physiologic basis of  ERG <ul><li>C wave – </li></ul><ul><li>-  RPE – in response to rod signals only </li></ul><ul><li>- ...
Amplitude  Implicit time
Recording protocol <ul><li>Full mydriasis </li></ul><ul><li>30 min dark adaptation </li></ul><ul><li>Rod response / scotop...
ERG recording <ul><li>Electrodes   active, reference, ground </li></ul><ul><li>Ganzfeld bowl stimulator </li></ul><ul><li...
 
Factors influencing ERG <ul><li>1 .  Stimulus –   </li></ul><ul><li>- a wave increase in size </li></ul><ul><li>- b wave r...
Factors influencing ERG <ul><li>2 .  Recording equipment -   </li></ul><ul><li>3. Dark  adaptation  –  </li></ul><ul><li>-...
Cone Rod ERG <ul><li>In light adaptation 6-8 million cones tested </li></ul><ul><li>In dark- additional 125 million rods c...
Separation of cone & rod ERG <ul><li>For clinically useful information </li></ul><ul><li>Cone ERG   flickering stimulus 3...
ERG recording <ul><li>Normal Waveforms   Rod response / scotopic blue / dim white  are usually smoother, dome shaped. Ini...
ERG recording <ul><li>Max combined response / scotopic white flash / mesopic response  is a deep ‘a’ wave with tall ‘b’. L...
ERG recording <ul><li>Oscillatory potentials    </li></ul><ul><li>Single flash cone response / photopic white flash   sm...
Clinical  Applications <ul><li>1. Diagnosis and prognosis of retinal </li></ul><ul><li>disorders  – </li></ul><ul><li>a. R...
Clinical  Applications <ul><li>2.To assess retinal function  when fundus  </li></ul><ul><li>examination is not possible </...
EOG
EOG <ul><li>Measurement of resting potential of eye </li></ul><ul><li>Which exist between cornea and back of </li></ul><ul...
EOG <ul><li>First discovered by  Du Bois-Raymond  (1849) </li></ul><ul><li>Riggs  (1954) &  Francois  worked extensively <...
EOG recording <ul><li>Dilate (>3 mm) </li></ul><ul><li>Skin electrodes near both canthi of BE </li></ul><ul><li>Ground ele...
EOG recording
EOG recording <ul><li>Base line. Keep lights on for 5 min </li></ul><ul><li>Turn  off  the lights. Record for 15 min in da...
EOG <ul><li>Potentials decrease progressively reaching lowest value called  ‘dark trough’  in 8-12 min </li></ul><ul><li>L...
EOG
Arden’s ratio <ul><li>Light peak / dark trough X 100 </li></ul><ul><li>>180%  Normal </li></ul><ul><li>165—180%  Borderlin...
<ul><li>Light sensitive  –  [ Light peak ] </li></ul><ul><li>-  Contributed by rods and cones  </li></ul><ul><li>B)  Light...
EOG <ul><li>Indications </li></ul><ul><li>Best dystrophy   markedly reduced with Arden ratio is less than 120% </li></ul>...
Visually Evoked Potential (Response) VEP / VER
Visual evoked potential <ul><li>Gross electrical signal generated at visual cortex in response to visual stimuli </li></ul...
Types of VEP <ul><ul><li>Pattern VEP  (checker-board patterns on TV monitor) </li></ul></ul><ul><ul><li>Flash VEP  (diffus...
VEP <ul><li>Un-dilated pupils. Sit 1 meter from monitor  </li></ul><ul><li>Electrodes in midline at forehead, vertex & occ...
 
VEP <ul><li>Normal waveform </li></ul><ul><li>Pattern VEP  has initial –ve ( N 1 )   +ve( P 1 )  second –ve ( N 2 ) wave...
 
 
VEP Indications <ul><li>Un-explained visual loss </li></ul><ul><li>Optic neuritis </li></ul><ul><li>Multiple sclerosis </l...
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Electrodiagnostic Tests in Ophthalmology

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Electrodiagnostic Tests in Ophthalmology are being frequently used now a days. Here we present a seminar on the same.

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Electrodiagnostic Tests in Ophthalmology

  1. 1. ELECTRO-DIAGNOSTIC TESTS ( ERG, EOG, VER ) Dr. Ankit M. Punjabi DOMS (final year) Dept. of Ophthalmology, KIMS Hospital Bangalore, Karnataka, INDIA Email: drankitalways@gmail.com
  2. 2. ERG <ul><li>Electric potential generated by retina in response to stimulation of light. </li></ul><ul><li>First recorded by Frithiof Holmgren (1865) </li></ul><ul><li>In humans by Dewar (1877) </li></ul><ul><li>Extensive work thereafter by Riggs (1941) </li></ul>
  3. 3. ERG waves ( a, b, c ) <ul><li>‘ a’ is negative wave. Amplitude is from baseline to trough & implicit time is from onset of stimulus to trough of ‘a’ wave </li></ul><ul><li>‘ b’ is large positive wave. Amplitude is trough of ‘a’ to peak of ‘b’ & implicit time is from onset of stimulus to peak of ‘b’ </li></ul><ul><li>‘ c’ is lower amplitude, prolonged +ve wave less imp </li></ul>
  4. 4. ERG
  5. 5. ERG <ul><li>‘ a’ origin  photoreceptors </li></ul><ul><li>‘ b’ origin  Muller’s cells + bipolar cells. Mainly from Muller’s in response to increase (ECF) K + in bipolars </li></ul><ul><li>‘ c’ origin  RPE </li></ul><ul><li>Oscillatory potentials (small wavelets on ascending limb of ‘b’) from amacrine cells </li></ul>
  6. 6. Physiologic basis of ERG <ul><li>a wave – </li></ul><ul><li>- Light falling – Hyperpolarisation </li></ul><ul><li>- Outer portion of photoreceptor – positive </li></ul><ul><li>- Inner portion - negative </li></ul><ul><li>- Blue dim flash - Rod ERG </li></ul><ul><li>- Bright red light - Cone ERG </li></ul>
  7. 7. Physiologic basis of ERG <ul><li>b wave- </li></ul><ul><li>- Muller cells – modified astrocytes </li></ul><ul><li>- No synaptic junction </li></ul><ul><li>- Respond to potassium concentration </li></ul><ul><li>- Change in membreane potential </li></ul><ul><li>- Cells provide b wave from rods and cones </li></ul><ul><li>- Oscillatory potential </li></ul>
  8. 8. Physiologic basis of ERG <ul><li>C wave – </li></ul><ul><li>- RPE – in response to rod signals only </li></ul><ul><li>- Direct contact of rod cells with RPE </li></ul>
  9. 9. Amplitude Implicit time
  10. 10. Recording protocol <ul><li>Full mydriasis </li></ul><ul><li>30 min dark adaptation </li></ul><ul><li>Rod response / scotopic blue/dim white </li></ul><ul><li>Max. combined response / scotopic white </li></ul><ul><li>Oscillatory potentials </li></ul><ul><li>10 min of light adaptation </li></ul><ul><li>Single flash cone response / photopic white flash </li></ul><ul><li>30 Hz flicker </li></ul>
  11. 11. ERG recording <ul><li>Electrodes  active, reference, ground </li></ul><ul><li>Ganzfeld bowl stimulator </li></ul><ul><li>Signal averager </li></ul><ul><li>Amplifier </li></ul><ul><li>Display monitor </li></ul><ul><li>Printer </li></ul>
  12. 13. Factors influencing ERG <ul><li>1 . Stimulus – </li></ul><ul><li>- a wave increase in size </li></ul><ul><li>- b wave reaches maximum </li></ul><ul><li>- Shortening of latency of peaks </li></ul><ul><li>. Flickering light – cone response only </li></ul>
  13. 14. Factors influencing ERG <ul><li>2 . Recording equipment - </li></ul><ul><li>3. Dark adaptation – </li></ul><ul><li>- ERG increases in size </li></ul><ul><li>- b wave becomes slower </li></ul><ul><li>4. Age and sex – </li></ul><ul><li>- small ERG within hr of birth , declines in adults </li></ul><ul><li>- Larger in females than males </li></ul>
  14. 15. Cone Rod ERG <ul><li>In light adaptation 6-8 million cones tested </li></ul><ul><li>In dark- additional 125 million rods contribute </li></ul><ul><li>In dark adaptation initial 6-8 min majority of response is from cones </li></ul><ul><li>Orange-red stimulus  cone + rod response </li></ul><ul><li>White flicker at 30 Hz with intensity constant only cones respond. As the freq increases ‘b’ amplitude decreases </li></ul>
  15. 16. Separation of cone & rod ERG <ul><li>For clinically useful information </li></ul><ul><li>Cone ERG  flickering stimulus 30-70 Hz (rods upto 50 Hz) </li></ul><ul><li>Rod ERG  in dark adaptation / blue light </li></ul>
  16. 17. ERG recording <ul><li>Normal Waveforms  Rod response / scotopic blue / dim white are usually smoother, dome shaped. Initial –ve ‘a’ wave is not seen & is hidden by ‘b’. Longer implicit time. Only rods contribute </li></ul>
  17. 18. ERG recording <ul><li>Max combined response / scotopic white flash / mesopic response is a deep ‘a’ wave with tall ‘b’. Longer implicit, larger amplitudes. Both rods & cones contribute </li></ul>
  18. 19. ERG recording <ul><li>Oscillatory potentials  </li></ul><ul><li>Single flash cone response / photopic white flash  small ‘a’ & ‘b’ waves. Waveforms are more peaked with shorter implicit & smaller amplitude. Cone function </li></ul><ul><li>30 Hz flicker multiple peaked waveforms. Cone function </li></ul>4 5
  19. 20. Clinical Applications <ul><li>1. Diagnosis and prognosis of retinal </li></ul><ul><li>disorders – </li></ul><ul><li>a. Retinitis pigmentosa </li></ul><ul><li>b. Diabetic retinopathy </li></ul><ul><li>c. Retinal detachment </li></ul><ul><li>d. Vascular occlusions of retina </li></ul><ul><li>e. Toxic and deficiency status </li></ul>
  20. 21. Clinical Applications <ul><li>2.To assess retinal function when fundus </li></ul><ul><li>examination is not possible </li></ul><ul><li>- Corneal opacities </li></ul><ul><li>- Dense cataract </li></ul><ul><li>- Vitreous haemorrhage </li></ul>
  21. 22. EOG
  22. 23. EOG <ul><li>Measurement of resting potential of eye </li></ul><ul><li>Which exist between cornea and back of </li></ul><ul><li>the retina during fully light adapted and </li></ul><ul><li>Fully dark adapted conditions. </li></ul>
  23. 24. EOG <ul><li>First discovered by Du Bois-Raymond (1849) </li></ul><ul><li>Riggs (1954) & Francois worked extensively </li></ul><ul><li>Arden & Fojas discovered importance of ratio </li></ul><ul><li>Records overall mass response only. </li></ul>
  24. 25. EOG recording <ul><li>Dilate (>3 mm) </li></ul><ul><li>Skin electrodes near both canthi of BE </li></ul><ul><li>Ground electrode at forehead. Lighted room </li></ul><ul><li>3 fixation lights 15 o apart (dim, red) </li></ul><ul><li>Looks left & right with 30 o excursion at rate of 15—20 rotations per minute . </li></ul>
  25. 26. EOG recording
  26. 27. EOG recording <ul><li>Base line. Keep lights on for 5 min </li></ul><ul><li>Turn off the lights. Record for 15 min in dark adapted state </li></ul><ul><li>Turn on the lights. Record for 15 min in light adapted state </li></ul><ul><li>Recordings sampled at 1 min intervals </li></ul><ul><li>Response decreases progressively during dark adaptation </li></ul>
  27. 28. EOG <ul><li>Potentials decrease progressively reaching lowest value called ‘dark trough’ in 8-12 min </li></ul><ul><li>Light insensitive part of EOG </li></ul><ul><li>Switch on  record in light adapted state </li></ul><ul><li>Progressive increase in potential, peak is called ‘light peak’ in 6—9 min </li></ul><ul><li>Light sensitive part of EOG </li></ul>
  28. 29. EOG
  29. 30. Arden’s ratio <ul><li>Light peak / dark trough X 100 </li></ul><ul><li>>180% Normal </li></ul><ul><li>165—180% Borderline </li></ul><ul><li><165% Subnormal </li></ul><ul><li>Difference of >10 % in BE is significant </li></ul><ul><li>Good pt cooperation is required </li></ul>
  30. 31. <ul><li>Light sensitive – [ Light peak ] </li></ul><ul><li>- Contributed by rods and cones </li></ul><ul><li>B) Light insensitive – [ Dark trough ] </li></ul><ul><li>- Contributed by RPE , Photoreceptors </li></ul><ul><li>inner nuclear layer </li></ul>2 components of EOG
  31. 32. EOG <ul><li>Indications </li></ul><ul><li>Best dystrophy  markedly reduced with Arden ratio is less than 120% </li></ul><ul><li>Butterfly pattern dystrophy </li></ul><ul><li>Chloroquine toxicity </li></ul><ul><li>Stargardt’s dystrophy </li></ul>
  32. 33. Visually Evoked Potential (Response) VEP / VER
  33. 34. Visual evoked potential <ul><li>Gross electrical signal generated at visual cortex in response to visual stimuli </li></ul><ul><li>Impulses carried to visual cortex via visual pathway </li></ul><ul><li>Recorded by EEG </li></ul><ul><li>It is the only objective technique to assess </li></ul><ul><li>clinical and functional state of visual syst.beyond </li></ul><ul><li>retinal ganglion cells. </li></ul>
  34. 35. Types of VEP <ul><ul><li>Pattern VEP (checker-board patterns on TV monitor) </li></ul></ul><ul><ul><li>Flash VEP (diffuse flash light for uncooperative subjects) </li></ul></ul>
  35. 36. VEP <ul><li>Un-dilated pupils. Sit 1 meter from monitor </li></ul><ul><li>Electrodes in midline at forehead, vertex & occipital lobes </li></ul><ul><li>2-3 different checker sizes are shown </li></ul><ul><li>Recording is done </li></ul>
  36. 38. VEP <ul><li>Normal waveform </li></ul><ul><li>Pattern VEP has initial –ve ( N 1 )  +ve( P 1 )  second –ve ( N 2 ) wave </li></ul><ul><li>Positive wave – 70 100 ms </li></ul><ul><li>Negative wave – 100 – 130 ms </li></ul><ul><li>Positive wave - 150 –200 ms </li></ul><ul><li>Flash VEP is complex. 2 positive & 2 negatives. </li></ul>
  37. 41. VEP Indications <ul><li>Un-explained visual loss </li></ul><ul><li>Optic neuritis </li></ul><ul><li>Multiple sclerosis </li></ul><ul><li>Compressive ON lesions </li></ul><ul><li>Cortical blindness </li></ul><ul><li>Amblyopia </li></ul><ul><li>Glaucoma </li></ul>
  38. 42. No one can drive you crazy unless you give them the keys
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