VSP Electroretinography

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VSP Electroretinography
2012-04-24 10:53:01

VSP Electroretinography
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  1. Records the temporal sequence of changes in the potential of the eye when the retina is stimulated with a brief flash of light.
  2. The ____ records changes in potential when the eye is moving; the ____ records changes of potential when a stimulus is presented.
    • EOG
    • ERG
  3. ERG and EOG measures ____ amplitudes of electrical responses
  4. A standard clinical protocol for recording ERG's was developed in _____ to make ERG's taken at different clinics and labs comparable
  5. The ___ is used primarily to diagnose retinal degenerations.
  6. During an ERG the electrodes are placed...
    on the cornea and the skin next to the eye
  7. A rapid decrease in the standing potential of the eye that occurs about 45 seconds to 1 minute after the onset of light.
    Fast oscillation (FO)
  8. In normal subjects FO is very sensitive to abrup changes in ?
    and is there an increse or decrease in the amplitude of FO?
    • bld glucose
    • increase
  9. The fast oscillation is generated by a light-evoked decrease in ____ ion concentration w/in the RPE and the accompanying hyperpolarization of the _____ .
    Chloride; basement membrane of the RPE
  10. Slow increase in the standing potential of the eye that peaks about 12 minutes after the onset of light is?
    Slow oscillation (SO)
  11. There is a ____ change in potential as the person is exposed to more retinal illumination for a long period of time.
  12. FO and SO are components of the ?
  13. EOG components make up the ___ part of the ERG wave?
  14. The most important components of the ERG in practice are?
    "a" and "b"
  15. When clinicians talk about the ERG they are generally referring to those changes in retinal potential that occur...
    within the first few seconds of a flash of light.
  16. The top line in an ERG is _____ and the bottom line is what happens with light ___. Which line is the only part you are looking at for the actual ERG?
    • light ONset
    • light OFFset
    • TOP LINE
  17. Who is known for testing the ERG of cats?
    Granit (1933)
  18. Granit separated the ERG into different parts of the wave into 3 parts:
    • P1
    • pII
    • PIII
  19. A slow "cornea positive" response, was first to disappear; meaning the curve deviates upward bc the cornea is more positive. What part is this?
  20. earlier "cornea positive" response, disappeared second; This response occurs before PI, this part of the curve doesn't disappear until there is more anesthesia.
  21. The "cornea negative" response that remains when the other two parts are extinguised). meaning the live of the graph deviates downward.
  22. WHY are there different parts of the ERG curve that take different amounts of anesthesia to disappear?
    because there is a specific part of the retina that dominates each part of the ERG waveform
  23. An experiment to determine which layers of the retina contribute to the ERG
    look in notes :P
  24. During normal ERG response, the ____ will hyperpolarize and the _____ _____ will depolarize.
    photoreceptors; cells outer to the photoreceptors
  25. "a" part of ERG wave is where the...
    photoreceptors hyperpolarize (get more negative)
  26. "b" part of ERG wave is where the...
    bipolar/Muller cells depolarize (get more positive)
  27. Types of electrodes:
    • Burian-allen
    • JET (disposable)
    • Gold Foil
    • DTL fiber
  28. Which electrode is commonly used in clinical practice; not disposable. Uses a ____ to keep eye open
    Burian Allen; speculum
  29. Why do you need a bowl shaped testing apparatus (Ganzfield bowl)?
    bc retina is curved

    ganzfield bowl acts as a diffuser that spreads light equally over parts of retina; curve of bowl makes light reflect in a way that illuminates all pts of the retina at once
  30. Standard procedure (Dark Adapted ERG)
    1. Dark adapt for ____ min
    2. ____ cornea
    3. ____ pupil
    4. Attach electorodes: 3 places
    5. Retina is illuminated with different __,__and ___ of flashed light stimuli
    6. ____ responses are obtained by the electrode and analyzed by computer
    7. If light adapted responses are obtained, they are done ____ the dark adapted responses.
    • 1. 35-40
    • 2. anesthetize
    • 3. dilate
    • 4. forehead (negative electrode), corneal (positive), behind ear (reference)
    • 5. wavelengths, intensities and rates
    • 6. electric
    • 7. after
  31. Burian Allen is used more often b/c
    has all 3 of the electrodes built in; doesen't have a separate ground/reference or separated electrodes
  32. results of an ERG sho responses to stimuli of _____.
    The numbers on right represent the intensity of the flash in ____.
    Top line is the ___.
    x- axis =
    y- axis =
    • varying brightness
    • Candelas/m2
    • Threshold response
    • x: milliseconds (timing of the wave)
    • y: uvolts (amplitude of waveforms)
  33. The threshold response is the ____ light that the patient's retina responded to.
  34. The very bottom line of ERG has a brightness that is _____ times brighter than the threshold stimulus.
  35. Dark adapted ERG to brief, high energy diffuse white flash.
    Standard ERG
  36. The standard ERG is dark adapted so that...
    the rods and cones are highly sensitive to light.

    (if you flash a very bright stimulus, you will get an optimal response from the photoreceptors)
  37. A white flash will ___ stimulate the rods and cones.
  38. a-wave is the leading edge of ...
  39. the a-wave curve gets more...
    negative (negative-going, cornea-negative)
  40. What structures in the retina cause the a wave?
    rods and cones
  41. which wave is the "receptor potential" or light-induced photoreceptor activity (ie: change in dark current). Photoreceptors hyperpolarize to light ONset...they make the potential more negative
  42. a-wave
  43. the largest component of diffuse flash ERG?
    B wave
  44. Light ONset Bipolar cells w/ some Muller cell contribution causes which wave?
  45. Which wave is positive-going or cornea-positive
  46. Which wave is positvie-going; slower
  47. This wave has two components: it has a smaller negative part which is caused by the neural retina and a larger positive part that is caused by the RPE...
  48. If there was something wrong with the c wave and the a&b waves were normal, you would suspect that there is something wrong with the ...
  49. the c wave is caused by
    Caused by light-evoked decrease in {K+] in subretinal space
  50. ERG measurement that measures the height of the wave reflects magnitude of the voltage change
  51. Measuring amplitude measures change in what?
  52. You measure the amplitude of the bwave by...
    measuring from the peak of the a wave to the peak of the bwave
  53. ERG measurement: time bw onset of the flash and peak of the wave
    Implicit time
  54. How is implicit time usually measured and why?
    Measured at the peak of the b wave; bc we usually only care about the a and b waves
  55. ERG measurement: time between stimulus onset and beginning of the a wave...
  56. see graphs in notes
  57. When we evaluate an ERG looking for changes from "normal" what 2 parameters do you look at in particular?
    amplitude and implicit time
  58. Amplitude is measure in?
    Implicit time is measured in ?
    • Microvolts
    • Milliseconds
  59. Which waveform is larger, rod or cones? Why?
    • Rods
    • There are much more rods than conces and they are much more sensitive under dark adaptation conditions
  60. What are some different types of ERGs that are used to separate the different parts of the retina and the different photoreceptors?
    • -diffuse flash
    • -focal fERG
    • -multifocal mfERG
    • -pattern PERG
  61. Why do we use different types of ERGs that are used to separate the different parts of the retina and the different photoreceptors?
    So we can analyze the health of each part of the retina
  62. This type of ERG can be applied to a dark- or light-adapted eye. Uses "standard" white, measures scotopic, scotopic balanced and photopic
    Diffuse flash
  63. If yo want to single out the cones you do what to the stimulus?
  64. Why do cones respond to a new flash of light sooner than a rod can?
    cones have a shorter recovery period
  65. Why are the magnitudes of an ERG different if it done under dark or light adapted conditions?
    In light adapted conditions, the rods are relatively bleached, so their response is dampened.
  66. Does a light adapted ERG have a larger or smaller amplitude than the dark adapted ERG?
    smaller amp
  67. Why is the magnitude of rod response to additional light limited under light-adapted conditions?
    response saturation
  68. This ERG is predominantly rod fundtion; dark adapted subject
  69. This ERG is predominantly cone function; light adapted subject
  70. What type of stimulus is used in a scotopic ERG?
    single, dim, blue flash

    (rods like blue light)
  71. What type of stimulus is used in a photopic ERG?
    single, red flash; high frequency flicker (>20Hz)
  72. Cones have the greatest ____ at the fovea, but ___% of cones are located OUTSIDE of the fovea
    density; 90%
  73. Greatest density of rods are how far away from the fovea
  74. How many million rods and cones are in the fovea; what proportion?
    rods: 120 million; cones: 9 million; 13 to 1
  75. When we use a bright white flash on a dark adapted retina 75% of the amplitude of the b wave comes from _______ and 25% of the amplitude of b wave comes from _______.
    • rods feeding into on-bipolars
    • cones " " '
  76. Which one, rods or cones, are sensitive to bright light? Have coarse visual acutity?
    cones, rods
  77. Maximal spectral sensitivity of rods? cones?
    • blue green (500nm)
    • green yellow (560 nm)
  78. Why do you use a red flash or red flickering light to test cones rather than greenish yellow?
    • because it further reduces the likelihood that rods will detect it
    • (rods are still somewhat sensitive to greenish yellow wavelengths)
  79. What is the result of a scotopic ERG?
    No a wave ; b wave with smaller amplitude

    (cone's contriubte to about 25% of bwave)
  80. What is the result of a photopic ERG?
    b wave has a much smaller amplitude (rods make up 75% of normal b wave!)
  81. Is a pt light or dark adapted during a photopic ERG?
    light adapted
  82. This can be used to characterize diseases that have a predilection for either rods or cones...
    Scotopic balancing
  83. If a long wavelength, red, light produces an ERG with the same amp as does a short wavelength (blue) light in a dark adapted animal, then the stimuli are said to be ___ ____
    scotopically balanced
  84. What are somethings you have to do to scotopically balance your ERG equipment?
    • -dark adapt a NORMAL subject
    • -record ERGs to dim, blue and red flashes
    • -equate response amps by dimming blue flash as needed
    • -use a dim white white background
  85. In an ERG which flash, blue or red, will elicit a higher amplitude? Why?
    Blue, because there are more rods

    (so in scotopic balancing you have to dim blue flash as needed to equalize amps)
  86. If the ERG's of the patient does not have equal amps for the red and blue stimuli, after scotopically balancing your equipment, then you can conclude that your patient's...
    retinal function is not normal
  87. In a scotopically balanced ERG what will a normal pts amplitude response look like to a blue and red stimuli in dark and light adaptation?
    Will have an equal amplitude
  88. In a scotopically balanced ERG what will a pt with a cone dystrophy, amplitude response look like to a blue and red stimuli in dark and light adaptation?
    lower amp response to the red light than the blue light
  89. -Dark adapted subject
    -single, bright, white flash (5ms)
    -Mix of photopic and scotopic response components
    The Standard ERG
  90. For a standard ERG how many a and b waves are there and why?
    • 2, because there are photopic and scotopic parts of the ERG
    • ap, as, bp, bs
  91. During a standard ERG, what parts of the ERG happens first?
    the parts of the ERG caused by the cones happen before the rods (as bs)
  92. What are the components of a Standard Flash ERG?
    • -Early receptor potential (ERP)
    • -a wave
    • -Oscillatory potentials (OPs)
    • -b-wave
    • -Afterpotential
    • -c-wave
  93. This portion of the standard ERG occurs before the a wave, is caused by the photoreceptors (outer segm or pigment)
    Early Receptor Potential (ERP)

    (picking up the potential change caused by the reaction of photopigm to light)
  94. This portion of the standard ERG is cuased by the photoreceptors, there are separate waves for photopic & scotopic conditions.
    a wave
  95. This portion of the standard ERG are on the ascending limp of b waves when generated with a bright flash. Caused by the inner plexiform layer (?amacrine cells?)
    Oscillatroy potentials (OPs)
  96. This portion of the standard ERG is caused by bipolar and muller cells; separate ones for photopic and scotopic conditions.
    b wave
  97. This portion of the standard ERG is on the descending limp of the bwave where ERG goes below baseline voltage
  98. This portion of the standard ERG is caused by the RPE
    c wave
  99. The a and b waves are ___ ___ frequency signals
    low temporal
  100. If we filter out the low Temporal freq (<100 Hz) then we filter out the large a and b waves and reveal the...
    oscillatroy potentials (high frequency) in the signal
  101. When recording oscillatory potentials what do you have to do to obtain the results?
    • dark adapt pt; bright white flash (the brighter the flash, the more OPs are generated)
    • apply a high pass filter to ERG response(lets the high temp freq through and filters out low)
  102. Where in the retina is the origin of the OPs?
    IPL (?amacrine cells?)

    story about prostate sx
  103. What is the clinical relevance of OPs?
    OPs are very sensitive to ischemia; OPs are severely attenuated or abolished by specific experimental conditions or pathologies, suggesting that each could represent a separate electrical event, structure or pathway
  104. Review notes for calulation for light flicker...
  105. Rods can't detect flicker that is faster than...
    20 Hz
  106. What type of stimulus, light adaptation is used during a Scotopic Threshold Response (STR)?
    fully dark adapted eye, very dim (near threshold), full field flash
  107. What happens under the conditions used during a Scotopic Threshold Response (STR)?
    There is a negative dip in the ERG after the b wave; there is only a STR when the stimulus is very dim.
  108. What two diagnoses can have an abnormal STR?
    • -Juvenile X-linked Retinoschisis (splitting bw retinal layers)
    • -Early diabetic retinopathy
  109. Focal ERG focuses on a...
    small part of the retina
  110. During a focal ERG what type of stimulus is used, what is requred and what is a problem?
    • small, flickering spot
    • Signal averaging required (filtering out the normal neural noise that is present in the retina)
    • stray light is a problem (bc you are testing a specific area)
  111. Focal ERG is used to test for...
    macular disorders, but can be applied to any small area of the retina (~10 deg. diameter)
  112. Epiretinal membrane (ERM)
    look at in notes
  113. Multifocal ERGs use what stimulus?
    hexagons, change from white to black and back (1 uvolt scale)
  114. A mfERG is color coded according to ____. A normal person will have higher amps at the ___.
    amplitude; fovea

    (ex. response of macula is gone w/ pt with ARMD)
  115. This type of ERG uses JET, gold foil or DTL fiber electrode and why are these electrodes used?
    Pattern ERG (PERG) bc you need a clear optical path (they don't get in the way like the othe electrodes do) you can't have cataracts or a cloudy cornea
  116. What stimulus is used for a PERG and what is the response origin?
    • pattern (contrast) reversal stimulus (black/white squares that alternate)
    • Tests: inner retina, mainly GANGLION cells
  117. What is the clinical relevance of a PERG, what diseases is it abnormal in?
    Glaucoma, CRA occlusion, Optic nerve trauma
  118. Look at notes for description and graph of PERG
  119. What layer of the retina does the c wave represent?
    pigment epith
  120. What layer of the retina does the a wave represent?
  121. What layer of the retina does the b wave represent?
    Muller cells, ON bipolar cells
  122. What layer of the retina does the OPs represent?
    amacrine cells
  123. What layer of the retina does the d wave represent?
    OFF bipolar cells