ERG – Electroretinography

Did you know it takes 100 milliseconds for information to reach from the eye to the back of the head!


ERG is a specialised eye test that detects the function of the light receptors rods and cones as well as detects function of the ganglion cells that transmits light signal to the visual cortex.

It measures the function of living cells that can recover.

With ERG we can measure the time it takes for signal to reach the visual cortex. With optic neuritis or optic nerve toxicity the latency of the signal exceeds >120 milli-seconds. Risk of developing Multiple sclerosis after episodes of optic neuritis is 50%.


ERG measures early dysfunction or weakness of retinal ganglion cells. At Radlett opticians we are able to detect early retinal changes and action a referral for patients to be treated with eye drops or SLT.

This early action would prevent death of retinal ganglion cells and eventually visual field loss. Glaucoma can therefore be reversed with early intervention.


Hydroxychloroquine (Plaquenil) is utilised in a number of auto-immune conditions such as rheumatoid arthritis, Lupus, Sjogren’s syndrome etc.

Using Multifocal ERG we can detect early retinal changes before it causes central vision loss.

Studies have shown that retinal toxicity such as Bulls eye maculopathy or visual field loss was 7.5% over 5 years use. Risk increased to almost 20% after 20 years but with higher doses this doubled to 40%.