 Expertise provided by Dr Dianne Sharp
Just as an electrocardiogram (ECG) offers valuable information
to the physician treating a patient with heart problems, ophthalmic
electrodiagnostic tests provide information about the function
of the visual system from the retina at the back of the eye, through
the visual pathways to the visual centre in the brain.
Information from electrodiagnostic tests can assist the eye specialist
with the diagnosis and recommendations for treatment for patients
with retinal and visual pathway disorders. The tests also provide
the specialist with information from which the prognosis and inheritance
pattern of their disorder can be made.
Electroretinogram (ERG)
The electroretinogram (ERG) is the most direct and objective
test available for evaluating the function of the retina. Electrodes
are placed on the skin around the eye and a soft gold foil electrode
is positioned over the lower lid to be in contact with the cornea
through the tear film. This is readily tolerated by adults and
children as young as 4 years old. Babies can be tested with an
electrode taped to the lower lid. Flashes of light are presented
under dark and light adapted conditions to separate the rod (night
vision) and cone (colour vision) systems of the retina. Both the
timing and the size of the ERG responses give valuable information
about the extent and nature of retinal abnormalities.
By changing the stimulus to a flickering chequer-board pattern
on a TV monitor screen a pattern ERG is obtained. The resulting
waveform reflects central vision or macular function and enables
diagnosis and a quantitative assessment of early macular disease
as well as the differentiation between localised macular disease
and more widespread retinal disease.
The ERG has been the gold standard for evaluating night blindness,
pigment changes in the retina, and colour vision disorders, enabling
the diagnosis of inherited retinal diseases before changes are
seen in the eyes. It is also recognised as an important tool for
the diagnosis and management of a wide range of common retinal
diseases. The ERG can help to distinguish peripheral retinal disease
from diseases localised to the central retinal or optic nerve.
The ERG is being used increasingly to identify vision-threatening
changes in diabetes and in central retinal vein occlusions. The
potential of the retina can be assessed through opacities such
as advanced cataracts, vitreous haemorrhage or in eyes after severe
trauma and early toxic damage from various causes involving the
retina can be detected with the flash ERG or pattern ERG.
Electro-oculogram (EOG)
Other areas of the visual pathway can be investigated by specific
electrical tests. The electro-oculogram (EOG) tests abnormalities
of the outermost layer of the retina, the retinal pigment epithelium,
allowing the early diagnosis of some inherited macular diseases
such as Bests disease.
Cortical Visual Evoked Potential (VEP)
The cortical visual evoked potential (VEP) provides information
about the health and function of the visual pathways from the
optic nerve as it leaves the back of the eye, to the visual centre
in the brain.
Many people require a combination of these tests to give complete
information about their visual problem.
Ophthalmic Electro-Diagnostic Tests
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| Global retina(Rods and
cones) |
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| Macular (central retinal)
function |
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| Retinal Pigment epithelium |
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Visual pathway
(Optic
nerve to visual centre
in brain) |
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To make an appointment, or
to find out more information, fill out our enquiry
form, or contact Eye Institute's
friendly team on free phone 0800 393 527.
Affiliated provider benefit to Cataract Patients
- no need for prior approval
- no money up front for surgery
- Southern Cross pays us directly
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