Electrophysiology Reference Card: ERG, EOG and VEP Patterns
Last updated: October 2026
Which test answers which question, what the waveforms mean, and the classic patterns to recognise. Normal values are laboratory-specific: always compare with the lab's own age-matched range.
Which test for which question?
| Test | What it tests | Use it for |
|---|---|---|
| Full-field ERG (ffERG) | Mass response of rods and cones across the whole retina | Retinitis pigmentosa and other dystrophies, CSNB, cone dystrophy, drug toxicity (e.g. vigabatrin), unexplained night blindness |
| Pattern ERG (PERG) | Macular function (P50) and ganglion cells (N95) | Separating macular from optic nerve causes of poor vision |
| Multifocal ERG (mfERG) | Cone function mapped across the central 30–50° | Hydroxychloroquine toxicity, occult macular dystrophy, AZOOR |
| EOG | RPE function (light rise / dark trough) | Best vitelliform dystrophy |
| VEP | The whole visual pathway to the occipital cortex | Optic neuritis and demyelination, compressive lesions, non-organic loss, infants |
ISCEV full-field ERG: the standard responses
| Step | Adaptation and flash | Mainly reflects |
|---|---|---|
| DA 0.01 | Dark-adapted, dim flash | Rod bipolar cells (b-wave only) |
| DA 3.0 (and DA 10) | Dark-adapted, bright flash | Combined rod-cone: a-wave = photoreceptors, b-wave = bipolar (inner retina) |
| DA oscillatory potentials | Dark-adapted | Amacrine cells; reduced in ischaemia (e.g. diabetic retinopathy) |
| LA 3.0 | Light-adapted single flash | Cone system |
| LA 30 Hz flicker | Light-adapted flicker | Cone system (rods cannot follow 30 Hz) |
Dark adaptation for at least 20 minutes before scotopic steps, and light adaptation for 10 minutes before photopic steps (ISCEV standard).
Classic patterns
| Pattern | Conditions |
|---|---|
| Negative ERG (b-wave smaller than a-wave in the DA bright flash) | Complete and incomplete CSNB, X-linked retinoschisis, CRAO, melanoma-associated retinopathy (MAR), quinine toxicity, Batten disease (CLN3), birdshot chorioretinopathy (some) |
| Rods affected more than cones, delayed flicker | Retinitis pigmentosa (often reduced long before visible fundus change) |
| Cones affected, rods normal | Cone and cone-rod dystrophy, achromatopsia (flicker almost absent) |
| Extinguished ERG in an infant | Leber congenital amaurosis |
| Normal ffERG with abnormal PERG P50 or mfERG | Macular disease (e.g. Stargardt, occult macular dystrophy, HCQ toxicity) |
| Normal ffERG and P50, reduced PERG N95 | Ganglion cell or optic nerve disease |
| Abnormal EOG with normal ERG | Best vitelliform dystrophy (the defining pattern). Arden ratio typically under about 1.5; normal is usually about 1.8 or more (lab-specific). |
| Reduced oscillatory potentials | Diabetic retinopathy, ischaemic retinopathies |
VEP quick guide
- Pattern-reversal VEP P100 latency is about 100 ms in healthy adults; the lab's upper limit is usually around 110–118 ms.
- Delayed latency with preserved amplitude: demyelination (optic neuritis, multiple sclerosis); latency often stays delayed after vision recovers.
- Reduced amplitude: axonal loss, ischaemic or compressive neuropathy, or poor fixation, uncorrected refraction or media opacity.
- Flash VEP is used when pattern VEP is not possible (infants, very poor vision, uncooperative patients).
- A normal pattern VEP at small check sizes in a patient claiming very poor vision suggests non-organic loss.
Before ordering: write the clinical question on the request ("is the macula or the optic nerve the cause of 6/36 vision?"). The lab will choose the right protocol, and dilated pupils (for ERG) or undilated pupils with best refraction (for pattern VEP) must be arranged accordingly.
Related: electro-oculography, normal values and optic neuritis vs NAION.
Key sources
- Robson AG et al. ISCEV standard for full-field clinical electroretinography (2022 update). Doc Ophthalmol 2022;144:165–77
- Constable PA et al. ISCEV standard for clinical electro-oculography (2017 update). Doc Ophthalmol 2017;134:1–9
- Odom JV et al. ISCEV standard for clinical visual evoked potentials (2016 update). Doc Ophthalmol 2016;133:1–9
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