by What is Electroretinography?
Electroretinography (ERG) is a diagnostic test used to measure electrical activity in the retina of the eye. ERGs are used to detect diseases that affect the photoreceptors and bipolar cells of the retina such as retinitis pigmentosa, macular degeneration, and diabetes. The ERG results help ophthalmologists diagnose these retinal diseases and monitor their progression over time.
How is an ERG performed?
An ERG involves placing contact lens electrode on the surface of the eye to detect electrical signals from retinal cells in response to flashes of light or patterns. This allows physicians to objectively measure retinal function without relying on a patient’s subjective responses. During the test, the patient lies down comfortably while the corneas are anesthetized with eye drops for comfort. The electrodes are gently placed on the cornea which is kept moist. Visual stimuli in the form of flashes or patterns of light are then presented to the patient. The electrical responses from the retina are recorded from the surface of the corneas and analyzed. The entire test takes about 30-45 minutes.
Types of ERG tests
There are different types of ERG tests that look at the function of specific retinal layers and cells:
Full-field ERG: Measures the Global Electroretinogram overall retinal response and is useful for diagnosing widespread retinal disease. It involves recordings from the entire retina after exposure to broad flashes of light or patterns.
Multifocal ERG: Maps local retinal responses across different parts of the retina by using multiple flashes in different areas of the visual field. This helps detect local abnormalities in macular or retinal diseases.
Single-flash ERG: Measures the retinal response from a single flash and helps evaluate photoreceptor and bipolar cell function.
Oscillatory potentials: Records small waves on the descending limb of the b-wave on a single-flash ERG. Loss of these waves indicates inner retinal dysfunction that may precede vision changes.
Photic ERG: Measures the light-adaption ability of the retina which is affected in certain retinal diseases.
Understanding ERG waves
The electrical response recorded on an ERG has characteristic positive and negative waves that provide insights into retinal layer function:
A-wave: A negative wave representing the function of photoreceptor cells (rods and cones) in response to light flashes.
B-wave: A positive wave representing the function of ON bipolar cells which receive input from photoreceptors after light stimulation.
PIII component: Represents Müller cell function and shows up on dark-adapted ERGs. Loss indicates retinal stress or damage.
Clinical applications of ERG
ERG aids in the diagnosis and monitoring of several retinal diseases including:
Retinitis pigmentosa: Progression seen as decreasing a-waves and b-waves on full-field ERG over time.
Macular degeneration: Localized ERG changes seen in affected areas on multifocal/focal ERG mapping.
Diabetic retinopathy: Abnormalities seen as decreasing b-wave amplitudes.
Optic nerve diseases: Abnormal ERG indicates Retrobulbar optic neuritis or other optic nerve pathologies.
Other retinal dystrophies like chloroquine/hydroxychloroquine toxicity, fundus albipunctatus, and Best’s disease.
ERG also helps evaluate retinal toxicity of drugs under clinical trials as well as surgical and laser treatments for retinal diseases. It can detect subclinical retinal changes before vision changes occur. Serial ERG testing is useful to monitor disease progression and treatment response over time.
Global prevalence of retinal diseases
The prevalence of retinal diseases is increasing globally due to aging populations and longer life expectancies. According to recent estimates:
Age-related macular degeneration affects over 170 million people worldwide and is a leading cause of blindness.
Diabetic retinopathy afflicts over 95 million diabetics globally and remains the most common cause of new cases of blindness among working-age adults.
Retinitis pigmentosa affects nearly 2 million people globally and is a genetically heterogeneous group of retinal dystrophies causative of vision loss.
The rising numbers underscore the growing clinical need for diagnostic testing services like ERG worldwide to enable early diagnosis and treatment monitoring of these sight-threatening retinal conditions. With advances in portable ERG equipment, tele-ophthalmology can help expand diagnostic access to underserved rural populations as well. Sustained research into new therapeutic targets also holds promise to slow retinal disease progression globally.
In summary, electroretinography is an objective diagnostic technique that provides a window into retinal cellular function. ERG testing plays a vital role in evaluating many retinal diseases affecting millions worldwide. Advancing technologies now allow widespread clinical and research applications of ERG to detect retinal abnormalities early and monitor treatment responses more precisely over time. Continued study of ERG signatures may also yield insights into disease mechanisms and biomarkers for developing novel therapies in the future.
*Note:
1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile it
