Electroretinogram (ERG) Overview and Issues
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Questions and Answers

What is the minimum recommended recovery time in ordinary room illumination before beginning ERG testing?

  • 60 minutes
  • 20 minutes
  • 10 minutes
  • 30 minutes (correct)

    • Which ERG type specifically evaluates the rod-system response?

  • Light-adapted 3.0 ERG
  • Dark-adapted 0.01 ERG (correct)
  • Dark-adapted 3 ERG
  • Flicker ERG

    • Which condition can be diagnosed using an ERG when clinical findings do not match visual complaints?

  • Diabetic retinopathy
  • Unexplained visual loss (correct)
  • Retinal detachment
  • Cataracts

    • What does the ERG primarily measure?

    <p>Mass response of the retina (A)</p> Signup and view all the answers

    Which of the following is a limitation of ERG testing?

    <p>It cannot detect ganglion cell disorders. (C)</p> Signup and view all the answers

    What is the primary purpose of an electroretinogram (ERG)?

    <p>To detect the function of the retina (A)</p> Signup and view all the answers

    Which type of retinal cell is primarily involved in generating the a-wave in an ERG?

    <p>Photoreceptors (rods and cones) (D)</p> Signup and view all the answers

    Which response in the normal ERG is primarily associated with the inner retina?

    <p>b-wave (C)</p> Signup and view all the answers

    What does the implicit time in an ERG measure?

    <p>The interval from stimulus onset to b-wave peak (D)</p> Signup and view all the answers

    What specifically differentiates the isolated rod response in an ERG?

    <p>Stimulation with dim light below cone threshold (D)</p> Signup and view all the answers

    What role do Mueller cells play in the context of an ERG?

    <p>Transmit electrical signals from photoreceptors (B)</p> Signup and view all the answers

    Which component of the ERG waveform is derived from the retinal pigment epithelium?

    <p>c-wave (C)</p> Signup and view all the answers

    Which statement correctly describes the influence of high RPE resistance during an ERG?

    <p>It prevents summated current from escaping completely (D)</p> Signup and view all the answers

    What does pattern ERG primarily represent in terms of retinal activity?

    <p>Ganglion cell activity (D)</p> Signup and view all the answers

    Which waveforms are associated with pattern ERG responses?

    <p>P1 (P50) and N1 (N95) (D)</p> Signup and view all the answers

    What is the role of the ground electrode in the ERG setup?

    <p>To neutralize electrical interference (C)</p> Signup and view all the answers

    Which factor is NOT physiological and does NOT affect the ERG results?

    <p>Electrode type (C)</p> Signup and view all the answers

    According to ISCEV guidelines, what is one requirement for pupil preparation before ERG testing?

    <p>Pupils should be maximally dilated (C)</p> Signup and view all the answers

    What is one of the conditions that must be avoided before conducting ERG testing?

    <p>Strong red light exposure (A)</p> Signup and view all the answers

    Which electrode is used as the reference electrode in traditional ERG recordings?

    <p>Outer canthus electrode (A)</p> Signup and view all the answers

    What is the recommended adaptation time for dark adaptation before recording dark-adapted ERGs?

    <p>20 minutes (B)</p> Signup and view all the answers

    What is the primary purpose of the full-field ERG?

    <p>To evaluate retinal function in severely traumatized eyes (A)</p> Signup and view all the answers

    Which ERG technique is primarily used for detecting small focal lesions?

    <p>Focal ERG (D)</p> Signup and view all the answers

    What stimulus is used in the 30 Hz flicker response to filter rod contributions?

    <p>A flickering stimulus (B)</p> Signup and view all the answers

    In the maximal combined response, which waves are prominently recorded?

    <p>Both a wave and b wave (B)</p> Signup and view all the answers

    What defines the full-field ERG in terms of flash duration?

    <p>5 ms duration (A)</p> Signup and view all the answers

    What characteristic distinguishes the multifocal ERG from other ERG techniques?

    <p>It utilizes densely arranged hexagonal elements. (B)</p> Signup and view all the answers

    What is a significant limitation of the focal ERG in clinical settings?

    <p>It suffers from light scattering and poor signal to noise ratio. (A)</p> Signup and view all the answers

    Which condition does a non-recordable flash ERG indicate for visual prognosis?

    <p>Ominous sign for visual prognosis (D)</p> Signup and view all the answers

    Flashcards

    Maximal Combined Response

    Larger waveform from bright flash in dark adapted state, stimulating rods & cones.

    'a' Wave in ERG

    Negative wave generated during maximal combined response in ERG.

    'b' Wave in ERG

    Positive wave following the 'a' wave in the ERG response.

    Cone Responses

    Single flash response in light adapted state, suppressing rod contribution.

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    30 Hz Flicker Response

    Measure cone response by flickering stimulus in light adapted state.

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    Full-Field ERG

    Standard ERG assessing retinal function in traumatic or opaque eyes.

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    Focal ERG

    Detects small lesions missed by full field ERG via small stimuli.

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    Multifocal ERG

    Records retinal activity from hexagonal stimuli in topographic form.

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    mfERG

    Multifocal electroretinography measures retinal responses across multiple regions, correlating with visual field defects.

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    Pattern ERG

    A test focused on inner retinal activity, especially ganglion cells, differentiating optic nerve from macular disorders.

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    Electroretinogram (ERG)

    A test that detects retinal function using electrical signals from retinal cells.

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    Photoreceptors

    Specialized cells in the retina (rods and cones) that detect light.

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    PERG Waveforms

    Components of pattern ERG representing the initial positive (P1) and subsequent negative (N1) corneal responses in milliseconds.

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    Active Electrode

    Electrode placed directly on the cornea in flash ERG and in the conjunctival sac for pattern ERG.

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    a-wave

    The initial negative deflection in ERG, signifying activity from photoreceptors.

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    b-wave

    A positive deflection in ERG, mainly from inner retina cells like Muller cells.

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    Ground Electrode

    The electrode placed on the forehead acting as a neutral reference point during ERG testing.

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    c-wave

    A wave in ERG derived from retinal pigment epithelium and photoreceptors.

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    Physiological factors in ERG

    Variables that can affect ERG results include age, pupil size, and dark adaptation.

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    Clinical Protocol (ISCEV)

    Guidelines specifying patient preparation, dark adaptation, and electrode placement for accurate ERG recording.

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    d-wave

    Wave in ERG indicative of off bipolar cells activity.

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    Artifacts in ERG

    Interfering factors that can affect ERG results, including blinking, eye movements, and air bubbles.

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    Oscillatory potentials

    Responses in ERG primarily from amacrine cells in the inner retina.

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    Isolated rod response

    Rod response observed with dark adaptation and dim light stimulation.

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    Recovery Time for ERG Testing

    Minimum 30 minutes recovery in normal room light before ERG.

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    Fixation in ERG

    Patients must look at a fixation point for stable gaze.

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    Dark-adapted ERG Types

    Includes 0.01, 3, and 10 ERG for rod responses and combined responses.

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    Indications for ERG

    Used to evaluate visual function and retinal conditions in various patients.

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    Limitations of ERG

    Cannot detect small or specific retinal lesions and certain ganglion cell disorders.

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    Study Notes

    Electroretinogram (ERG) Overview

    • ERG is an eye test assessing retinal function.
    • The retina is the light-sensitive layer at the back of the eye.
    • The retina contains specialized cells (photoreceptors, Muller cells, bipolar cells, and ganglion cells).
    • Photoreceptors (rods and cones) detect light.
    • Ganglion cells transmit images to the brain.
    • Muller and bipolar cells act as intermediaries.
    • ERG measures the electrical signals generated by these cells in response to light.

    Abnormal ERG Readings

    • Abnormal ERG readings indicate issues with retinal cell layers.
    • Medical professionals place an electrode on the cornea to measure these electrical signals.

    Basic Principle of ERG

    • Sudden light illumination activates retinal cells, generating current.
    • Currents generated from all retinal cells mix.
    • They travel through vitreous and extracellular spaces.
    • High RPE resistance prevents outward flow.
    • The small portion of current escaping through the cornea is recorded as ERG

    ERG Wave Forms

    • a-wave: initial corneal-negative deflection from cones and rods.
    • b-wave: corneal-positive deflection from inner retina mainly Muller & ON-bipolar cells.
    • c-wave: derived from the retinal pigment epithelium and photoreceptors.
    • d-wave: from off bipolar cells.

    Dark Adapted Oscillatory Potentials

    • Responses primarily from amacrine cells/inner retina.
    • Latency is the time from stimulus onset to a-wave beginning.
    • Implicit time measures the time from stimulus onset to b-wave peak.

    Generator Sites of the Flash ERG

    • The a-wave originates from the photoreceptor layer.
    • The b-wave is a glial potential originating from Müller cells and bipolar cells.
    • OPs originate from amacrine cells.
    • Flash ERG reflects electroretinal activity distal to the ganglion cell layer.

    Components of the Flash ERG

    • Implicit time (i.t.): Time from stimulus to peak of activity.
    • Amplitude (amp): Voltage magnitude at peak of activity.

    ERG Responses

    • A normal ERG includes 5 distinct responses:
      • Rod response
      • Maximal combined response
      • Oscillatory potentials
      • Single flash cone response
      • 30 Hz flicker response

    Isolated Rod Response

    • Produced by adapting the patient to darkness.
    • Stimulating retina with a dim light flash under specified conditions.
    • The resultant waveform exhibits a prominent b-wave and no detectable a-wave.

    Maximal Combined Response

    • Generated by using a bright flash interval in a dark adapted state.
    • Prominent a and b waves, with superimposed oscillatory potentials.

    Cone Responses

    • Obtained by maintaining light adaptation and stimulating the retina with a bright white flash.
    • Rods are suppressed by light adaptation and do not contribute to the waveform.

    30 Hz Flicker Response

    • With the patient in a light-adapted state.
    • A flickering stimulus allows filtering rod response to measure cone response.

    Types of ERG (Specialized Forms)

    • Full-field ERG (Bright Flash ERG)
    • Focal ERG
    • Multifocal ERG
    • Pattern ERG

    Full-Field ERG (Bright Flash ERG)

    • Used for assessing retinal function in severely traumatized or dense media opacity eyes (like dense VH or corneal opacity, or advanced cataract.)

    Clinical Protocol (Procedure)

    • Pupillary dilation is necessary, and pupil size is measured before and after recording.
    • Pre-adaptation to light or dark (20 min dark adaptation and 10min light adaptation) is crucial for accurate recordings.
    • Extra dark adaptation is recommended following electrode insertion and corneal contact electrode use. Prior to ERG testing, fluorescein angiography, fundus photography, and other strong illumination tests are avoided.
    • At least 30min recovery time in ordinary room light is recommended after these tests before starting an ERG test.

    Fixation

    • Patients are instructed to fixate on the fixation point incorporated.
    • Stable gaze helps to avoid eye movements.
    • Look straight and maintain a steady gaze are important for avoiding artifacts. Any issues in eye opening or fixation is important to note.

    Electrodes

    • Ground: forehead (neutral)
    • Reference: Outer canthus (negative)
    • Active: Cornea (flash ERG) or Conjunctival sac (pattern ERG) (positive)

    Electrodes Used in ERG (Visual Aids)

    • Jet Electrode
    • Gold Plate Electrode
    • Skin Electrode
    • DTL Electrode
    • HK Loops
    • Electrode paste (e.g., Ten20)
    • Skin Prep Gel (e.g., Nuprep)

    Factors Affecting ERG

    • Physiological (pupil, age, sex, refractive error, diurnal variation, dark adaptation, anesthesia)
    • Instrumental (amplification, gain, stimulus, electrodes)
    • Artifacts (blinking, tearing, eye movements, air bubbles)

    Indications and Clinical Uses of ERG

    • Evaluating visual function in infants and children.
    • Determining retinal function presence or absence
    • Assessing retinal degeneration progression.
    • Confirming particular disease (dystrophies) diagnosis.
    • Detecting toxic retinopathies.
    • Assisting in diagnosing retinal conditions with inconsistent clinical findings and visual complaints (unexplained visual loss.)

    Limitations of ERG

    • ERG measures the mass response, not isolated lesions.
    • Lesions like hole hemorrhage, chorioretinitis, or localized retinal detachment are not readily detected by amplitude changes.
    • Disorders affecting ganglion cells, optic nerve, or striate cortex do not produce ERG abnormalities.

    Interpretation

    • Each lab has unique normal values dependent on age.
    • Interpretation must consider age-related factors.

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    Electroretinogram (ERG) PDF

    Description

    This quiz covers the fundamentals of the Electroretinogram (ERG) test, which assesses retinal function by evaluating the electrical signals generated by retinal cells in response to light. It also discusses the implications of abnormal ERG readings and the basic principles underpinning the test. Explore how various retinal cells contribute to vision through this diagnostic tool.

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