Electroretinogram (ERG) and Electrooculogram (EOG)

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  • 3 main types of electroretinograms (ERGs)
    • Full-field ERG (ffERG): Illuminates the entire retina uniformly
    • Pattern ERG (PERG): Utilizes a contrast stimulus, typically an alternating checkerboard pattern
    • Multifocal ERG (mfERG): Provides a topographic map of cone system function over approximately 50° of the retina
  • Characteristics of Full-field ERG
    • DA = Dark Adaptation
    • LA = Light Adaptation
    • 0.01 / 3.0 / 10.0 = Flash intensities, indicating the strength of the light flash
    • a-wave: Response of photoreceptors (negative wave)
    • b-wave: Response of Müller cells and bipolar cells (positive wave)
    • c-wave: Response of the retinal pigment epithelium (RPE), 2-4 seconds delayed, (positive wave)
      • occurs only in dark adaptation
    • Implicit time: Time from light stimulus to the peak of the b-wave (in milliseconds)

Overview ERG und PERG¹

  • DA 0.01: Rod-specific; b-wave, cannot differentiate between photoreceptors and inner retinal layers.
  • DA 3.0: Mixed rod-cone response; includes both a- and b-waves.
  • DA 10.0: a-Wave indicates photoreceptor function; differentiates between photoreceptor dysfunction and inner retinal dysfunction.
    • If DA 0.01 is reduced:
      • DA 10.0 a-wave reduced? -> photoreceptor dysfunction
      • DA 10.0 b-wave reduced? -> inner retinal dysfunction
  • LA 30 Hz: “photopic flicker” tests cone function
  • LA 3.0: “photopic single-flash” a-wave corresponding to cone photoreceptors and off-bipolar cells, b-wave with on/off-bipolar cells
  • PERG: Pattern ERG: contrast stimulus, typically an alternating checkerboard pattern at consistent brightness
    • Must be focused on the macula
    • e.g. LHON
    • Main components
      • P50: Amplitude allows objective assessment of macular function
      • N95: Measures central retinal ganglion cell function (RGCs)
    • Additional component: N35

Multifocal ERG¹

  • Topographic representation of the cone system over approximately 50°
  • Good fixation is important
  • e.g. for early detection of hydroxychloroquine retinopathy
  • a) Normal finding; b) Retinitis pigmentosa; c) Macular dystrophy; d) Enlarged blind spot in eccentric nasal retinal dysfunction


  • Diagnosis of generalized retinal degenerations
  • In cases of suspected reduced visual acuity and presence of nystagmus at birth
  • Measuring retinal function in cases of opaque media
  • If functional visual loss is suspected


  • Central Retinal Artery Occlusion (CRAO): Normal a-wave (as the photoreceptor layer is supplied by the choroid), missing b-wave
  • Ischemic Central Retinal Vein Occlusion (CRVO): Reduced amplitude of b-wave, extended implicit time
  • Retinitis Pigmentosa: Reduced amplitude (usually of the b-wave) and extended implicit time; in advanced stages -> no rod and cone response to bright light stimuli
  • Multiple Evanescent White Dot Syndrome (MEWDS): Reduced a-wave
  • Glaucoma, Congenital Rubella, Optic Atrophy/Neuropathy: Normal ERG (as ganglion cells are affected)

Electrooculogram (EOG)

  • Measures corneoretinal potential
  • Assesses the function of the RPE and the interaction of photoreceptors with RPE
  • Arden Ratio: Maximum potential height in light divided by minimum potential height in darkness
    • Normal: > 1.85/ > 185%
    • Pathological: < 1.65/ < 165%
  • The ERG is pathological in all cases where the EOG is abnormal except:
    • Normal ERG, pathological EOG:
      • Best’s disease as a classic example
      • Pattern dystrophies, Chloroquine retinopathy
    • Pathological ERG, normal EOG:
      • X-linked retinoschisis, CSNB (congenital stationary night blindness)

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