Electroretinography (ERG) Explained

Why is Electroretinography Important?

 

What is electroretinography (ERG)?

Electroretinography is an electrophysiological test of the retina, the layer of the eye which detects light. The electroretinogram (ERG) is to the retina what the electrocardiogram (ECG) is to the heart. Just as an ECG is crucial to diagnosing illness and monitoring the heart’s function, ERG plays a critical role in the care of the eye, and is instrumental in the early detection of retinal dysfunction.

Why does ERG matter?

Electroretinography provides a wealth of objective, vital information about retinal function and health. ERG plays a vital role in the diagnosis of acquired and inherited eye diseases, as well as fuel research into the factors that affect the health of the retina or the visual pathways.

What is an Electroretinogram?

The electroretinogram (ERG) is an examination that evaluates the function of the eye’s retinal cells. Patients’ eyes are stimulated with light and the resulting electrical activity from their retinal cells is measured by skin or corneal electrodes. Dependent on the type, intensity and colour of the light stimulus information on different areas and types of cells can be obtained.

 

3 Types of ERG Tests

There are 3 main types of ERGs: full-field flash ERG (ffERG), pattern ERG (PERG), and multifocal ERG (mfERG). Each has different applications and benefits. Determining the functional status of the retina with different typs of ERG testing allows clinicians and researchers to evaluate patients for retina-related conditions, reliably monitor retinal function over time, and evaluate the efficacy of retinal treatments. ERGs are used in human care, veterinary practices, and medical research.

Full-Field ERG

Full-field ERG

In full-field ERG (ffERG), electrodes record the summed electrical response of the retinal cells. The summed electrical response is a blend of the results from a range of different cells and regions in the retina, meaning that full-field ERG (ffERG) shows the status of the retina as a whole.

Pattern-ERG

Pattern ERG

In pattern ERG (PERG), the light stimulus is an alternating checkerboard pattern which evokes electrical responses from the ganglion cells composing the inner retina. PERG is commonly used as a test for disorders affecting ganglion cells, as well as many neurodegenerative disorders.[8]

Multifocal ERG

Multifocal ERG

Multifocal ERG (mfERG) is performed with a similar protocol to the PERG, but the light stimulus displays an array of hexagons that flicker between white and black in a pseudo-random sequence. The mfERG is best for measuring dysfunction of the central retina area and is not sensitive to abnormalities in the ganglion axon.[9]

Detect Functional Stress

Anticipate Structural Damage

 

How is ERG different than structural imaging?

Electroretinography objectively evaluates the functional abnormalities of the retina, while structural imaging shows the anatomy of the retinal tissue. While both functional and structural assessments have their benefits, functional changes generally appear well before structural changes. Catching retinal abnormalities quickly is critical for minimizing damage and maximizing vision retention, so functional assessments like ERG are important tools in the ophthalmic diagnostic suite.

Handheld ERG as a practical & effective diagnostic tool

Recent studies comparing ERG to structural imaging techniques show that ERG is an effective diagnostic tool. In studies comparing ERG and structural imaging’s abilities to evaluate sight-threatening diabetic retinopathy, the handheld and portable RETeval® device’s ERG results outperformed the traditionally-used imaging technique in predicting which patients would later need medical intervention.[13],[14] In an assessment of RETeval’s ability to evaluate diabetic retinopathy, the advantages of RETeval included earlier detection of retinal dysfunction, lower investment costs, and less required reading knowledge than the traditionally-used imaging technique.[15] An assessment of RETeval’s ability to evaluate central retinal vein occlusion found that RETeval ERGs are less invasive, easier to perform, and give more reliable predictions than the traditionally-used imaging technique.[16]

Advantages of ERG testing

The ease and sensitivity of ERGs performed with the handheld RETeval is highly preferred over imaging techniques in certain situations. Patients who have media opacities, poor cooperation, or small pupils are better able to be evaluated for retinal abnormalities with the RETeval[14]. Recent studies comparing ERG to structural imaging techniques show that ERG is an effective diagnostic tool. In studies comparing ERG and structural imaging’s abilities to evaluate sight-threatening diabetic retinopathy, RETeval ERGs outperformed the traditionally-used imaging technique in predicting which patients would later need medical intervention.[13],[14] In an assessment of RETeval’s ability to evaluate diabetic retinopathy, the advantages of RETeval included earlier detection of retinal dysfunction, lower investment costs, and less required reading knowledge than the traditionally-used imaging technique.[15] An assessment of RETeval’s ability to evaluate central retinal vein occlusion found that RETeval ERGs are less invasive, easier to perform and give more reliable predictions than the traditionally-used imaging technique.[16]

Non-invasive ERG testing

In an independent study comparing RETeval ERGs to conventional digital retinal photographs, the RETeval was chosen by patients as the method preferred over photography.[14] While many children need to be sedated to undergo conventional ERG, children as young as six months old have been able to remain calm during ERGs performed with RETeval.[18] The non-invasive nature of the ERG and the ease of the hand-held, non-mydriatic RETeval makes the ERG device a valuable screening tool for many ophthalmic pathologies.

Applications of Electroretinography

Electroretinography has an impressive range of human and animal applications, for both clinical and research uses. Our technology provides reliable, repeatable, and effective ERG solutions in all of these categories.

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