Electroretinography (ERG; electroretinogram) is a diagnostic procedure in ophthalmology. It reflects the electrical response of the sensory cells (cones and rods) in the retina of the eye to a light perception. Here, the light-dependent response and thus the functional state of the outer and middle retinal layers are measured in particular.
Indications (areas of application)
- Early detection and differential diagnosis of hereditary retinal or choroidal dystrophies (hereditary degenerative changes of the retina (retina) and choroid (choroid), for example, in:
- Retinitis pigmentosa (degeneration of the cones and rods).
- Sorsby’s fundus dystrophy
- Juvenile macular degeneration or Stargardt’s disease (rare retinopathy (retinal disease), where the center of the retina is affected as the site of sharpest vision (macula)).
- Cone dystrophy (diffuse retinal degeneration, as the cones of the entire retina (retina) are affected).
- Best’s disease (also vitelliform or ovoid macular dystrophy) – rare retinal degeneration in which the center of the retina is affected as the site of sharpest vision (macula).
In the usually variable course of these diseases, retinal degeneration occurs, which can lead to significant vision loss or blindness.
- Syndromes with retinal (retina) or choroidal (choroid) involvement:
- Retinitis (retinal inflammation).
- Retinochoroiditis (inflammation of the choroid and retina).
- Age-related macular degeneration (AMD) – degeneration of the sensory cells in the macula.
- Diabetic retinopathy
- Ablatio retinae (retinal detachment)
- Retinopathia centralis serosa (swelling-induced retinal detachment).
- Hypertensive retinopathy – retinal disease caused by hypertension (high blood pressure).
- Retinoschisis (splitting of the retina).
- Retinopathia praematurorum – retinal disease in premature infants.
- Acquired retinal degeneration (atrophy of the retina), melano-, carcinoma-associated retinopathy (tumorous changes of the retina (retina), e.g. retinoblastoma).
- Therapy control in birdshot chorioretinopathy (inflammatory disease of the choroid and retina).
- Intoxications (poisonings) – e.g. lead.
- Vitamin A deficiency
- Preoperative functional diagnostics (examination before surgery).
- Clarification of visual field defects of unclear origin.
The procedure
The eye is exposed to different light stimuli, which differ in intensity, frequency and background illumination. Thus, one is able to examine separately the rod system (dark adaptation) and the cone system (light adaptation, color perception). For the examination, the pupils are dilated with eye drops. The electrical response of the sensory cells is derived with electrodes. In ophthalmology (eye care), corneal electrodes (corneal electrodes) are usually used, but this requires corneal anesthesia (anesthesia of the cornea) and is therefore very costly. Alternatively, gold foil or platinum electrodes are used, which are inserted into the conjunctival sac or may be incorporated into a contact lens. Skin electrodes are considered too inaccurate.
ERG variants
- Flash ERG (classical method)
- Stimulus: white light flash of variable brightness and frequency; the flash ERG is used to study the function of the entire retina
- Pattern ERG
- Stimulus: high-contrast images, e.g., checkerboard pattern whose black and white squares are reversed approximately 3 times per minute; the pattern ERG allows functional testing of the retinal center and thus the macula (yellow spot, site of sharpest vision)
- Multifocal ERGs
- Stimulus: contrast pattern; small hexagonal areas of the retina are exposed. In this way, it is possible to very precisely stimulate sensory cells and check their function. Thus, especially the macular function is examined.
The ERG is a very useful method for functional diagnostics in ophthalmology. It provides valuable information about the condition of the retina or choroid and thus contributes to successful diagnosis and therapy in ophthalmology.
