Medically reviewed by Dr. Niranjana Bejan Singh. Written to established clinical-education standards (AAO/Mayo/NHS/NEI) and adapted for this hospital. Not a substitute for professional medical advice.
An electroretinogram (ERG) is a diagnostic test that measures the electrical signals generated by the light-sensing cells of the retina — the rods and cones — in response to flashes of light. It helps detect and characterise retinal conditions, including inherited retinal diseases, that can be difficult to diagnose from an eye examination alone, and is especially useful in young children or when the retina looks structurally normal but vision is poor.
Who typically needs this
- Children or adults with unexplained poor vision, night blindness, or eye-shaking (nystagmus) where the eye exam alone does not explain the symptoms.
- Patients with suspected inherited retinal conditions, such as retinitis pigmentosa, achromatopsia, or congenital stationary night blindness.
- Patients being monitored for known retinal disease progression, or for possible retinal effects of certain medications.
- Individuals with a family history of inherited retinal disease, to help characterise their own retinal function.
What to expect
- The pupils are usually dilated with eye drops before the test.
- Numbing (anaesthetic) drops are applied, and a special electrode — either a contact-lens-type sensor or a small electrode near the eye — is positioned to record the retina's electrical activity.
- The patient is exposed to a series of light flashes in both dark-adapted (rod-testing) and light-adapted (cone-testing) conditions.
- The full test typically takes between 30 and 90 minutes depending on the protocol used, and young children may need sedation to stay still.
Recovery
- Mild light sensitivity or blurred vision from the dilating drops can last a few hours after the test.
- There is no incision and no significant downtime; most patients resume normal activities the same day.
- Results are reviewed by the ophthalmologist alongside the clinical eye examination and any other tests to reach a diagnosis.
Risks to know about
- The test itself is not painful, but it requires the patient to cooperate and remain still, which can be difficult for very young or anxious children.
- Sedation, if used to help a young child stay still, carries its own standard, well-understood risks that will be discussed beforehand.
- The electrode touching the eye surface can cause temporary mild irritation or scratchiness afterward.
- ERG shows overall retinal electrical function rather than a detailed structural picture, so it is often combined with imaging tests (such as OCT) for a complete diagnosis.
Frequently asked questions
Is ERG painful for my child?
It is not painful, but it does require holding still with drops and an electrode in place, which can be challenging for very young children — sedation is sometimes used if needed.
Why does the test need a dark room?
Dark adaptation allows the rod photoreceptors, responsible for night and dim-light vision, to be tested separately from the cone photoreceptors used for daylight and colour vision.
Can ERG tell us the exact genetic condition?
ERG shows the pattern of retinal dysfunction, which helps narrow down the diagnosis, but genetic testing is often needed to confirm a specific inherited condition.
When will we get the results?
Your ophthalmologist will usually review the results at a follow-up visit, often alongside other test findings, and explain what they mean for your child.
Ready to see us?
Call the appointment desk, or book online — we will confirm your time by phone.
Sources consulted: NEI — Retinitis Pigmentosa, AAPOS — Electroretinogram (ERG) (Glossary) . General medical information — not a substitute for professional diagnosis. Medically reviewed by Dr. Niranjana Bejan Singh.
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